# AstroPhysics Seminar

Organizer(s)
Usual Time
Thursdays at 14:00 (Israel Time) for the Winter semester; Wednesdays at 14:00 during the Spring
Place
Physics Building (202) Seminar Room 303
More Details

When given on Zoom, the link is https://zoom.us/j/9290951953

All recordings appear online, here: https://www.youtube.com/playlist?list=PLCq9Go28tBlCFfRXw5WAmFYc7ORznISXj

If you'd like to give a talk, email ofek.birnholtz@biu.ac.il and/or asaf.peer@biu.ac.il and/or maayane.soumagnac@gmail.com

Upcoming Lectures
- Prof. Felix Ryde (KTH, Stockholm)
Prof. Felix Ryde (KTH, Stockholm)
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TBD

- Sarah Spitzer, University of Michigan, Ann Arbor
Sarah Spitzer, University of Michigan, Ann Arbor
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An inflow of interstellar neutral particles known as the interstellar wind is created as the Sun moves through the interstellar medium. This influences the composition of the Heliosphere, or the region of space affected by the Sun. After these neutrals enter the Heliosphere, they may become ionized by processes such as photoionization, electron impact ionization, and charge exchange with the solar wind. These “pickup” ions propagate radially outward with the solar wind. Studying distributions of these pickup ions is one of the most accessible means of studying Heliospheric ‒ interstellar interactions. One such feature that we measure to determine characteristics of this flow interaction is the helium focusing cone. Due to the high first ionization potential of helium, the focusing cone, a signature of enhanced helium which has been gravitationally focused on the downwind side of the Sun, leads to a measurable enhancement in the pickup ion population out to 1 AU. The Solar Orbiter Heavy Ion Sensor (SO-HIS) measures ions in the range H+ to Fe20+ with sufficient energy and angular ranges to measure characteristic signatures of pickup ions in the velocity distribution. To achieve our aim to study Heliospheric ‒ interstellar interactions using in situ pickup ion measurements, we present a characterization of the SO-HIS instrument required to enable identification of pickup ions in the data. We characterize the geometric factor and solid state energy detector efficiencies and develop validated pickup ion distribution measurements.

- Shahar Hadar, Oranim (Haifa University)
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TBD

- Sahar Shahaf, Weizmann Institute of Science
Sahar Shahaf, Weizmann Institute of Science
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TBD

- Daniel Pook-Kolb, Radboud University, Nijmegen, Netherlands
Daniel Pook-Kolb, Radboud University, Nijmegen, Netherlands
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TBD

- Yotam Sherf, BGU
Yotam Sherf, BGU
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TBD

- Itai Linial, Hebrew University of Jerusalem, Israel
Itai Linial, Hebrew University of Jerusalem, Israel
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TBD

Date is to be determined

Previous Lectures
- Angela Borchers Pascual, Albert Einstein Institute, Hannover, Germany
Angela Borchers Pascual, Albert Einstein Institute, Hannover, Germany
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.The accuracy of gravitational-wave models of compact binaries has traditionally been addressed by the mismatch between the model and numerical-relativity simulations. This is a measure of the overall agreement between the two waveforms. However, the largest modelling error typically appears in the strong-field merger regime and may affect subdominant signal harmonics more strongly. These inaccuracies are often not well characterised by the mismatch. We explore the use of a complementary, physically motivated tool to investigate the accuracy of gravitational-wave harmonics in waveform models: the remnant's recoil, or kick velocity. Asymmetric binary mergers produce remnants with significant recoil, encoded by subtle imprints in the gravitational-wave signal. The kick estimate is highly sensitive to the intrinsic inaccuracies of the modelled gravitational-wave harmonics during the strongly relativistic merger regime. We investigate the accuracy of the higher harmonics in four state-of-the-art waveform models of binary black holes. In this talk, I will present the results of our study and discuss how numerical-relativity kick estimates could be used to calibrate waveform models further.

- Antoine Claude Bret, Universidad de Castilla La Mancha
Antoine Claude Bret, Universidad de Castilla La Mancha
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According to MHD, a strong parallel shock is a few mean-free-paths thick, with a density jump of 4. The talk will comment on these 2 aspects for the case of a collisionless shock. First, I’ll review recent analytical works explaining how, as the plasma becomes collisionless, the front continuously switches from a few mean-free-path to a distance much shorter, in terms of the upstream plasma parameter. Second, I will also show how the density jump of a strong parallel collisionless shock can shrink to 2 instead of 4. This is due to the ability of a collisionless plasma to sustain a stable anisotropy in the presence of a magnetic field. PIC simulations will be presented confirming this conclusion.

- Jonathan Mushkin, Weizmann Institute of Science
Jonathan Mushkin, Weizmann Institute of Science
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As a part of the ongoing search for inspiraling black hole binaries in gravitational-waves data, we derive a scheme to obtain the optimal detection test-statistic (the evidence ratio) in a way that is efficient to compute both on the target signal and compute its exact properties using time-slides (time-shifting the detectors with respect to each other). This detection statistic, for the first time, includes the effects of both precession and high emission modes. Due to computational limitations, we employ the test for the 10^4 most promising candidates from the regular (fast) match-filtering pipeline. This is an improvement in both statistical significance and run-time compared to a previous scheme by the GW@IAS collaboration (Zackay et al. 2019). A key component of the new scheme is posterior probability estimation, commonly performed today by sampling algorithms (e.g. MCMC, Nested Samplers). Time permitting, we'll discuss recent developments in this area.

- Kartik Sarkar, The Hebrew University of Jerusalem
Kartik Sarkar, The Hebrew University of Jerusalem
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The origin of the Fermi/eROSITA bubbles still remains a debated question. One of the popular theories is that the bubbles are driven by a past AGN jet from the Sgr A*. A crucial assumption for the claimed jet is that the jet is launched along the rotation axis of the Galaxy despite several observational pieces of evidence indicating a different picture. In this talk, I will discuss the general effects of a misaligned jet in the Milky Way ISM. We find that the dissipation of the claimed jet within the ISM is an essential requirement for simultaneously producing the symmetrical features of the Fermi/eROSITA bubbles and the observed x-ray signatures. We show that hydrodynamic jets from Sgr A* fail to produce these features and therefore are ruled out. Other Blackhole driven mechanisms such as a magnetic jet, accretion wind, or TDEs, can in principle produce these features provided their power is ~ 10^{40.5-41} erg/s.

- Oren Slone, Princeton & NYU
Oren Slone, Princeton & NYU
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Sub-galactic astrophysical structure provides probes into the microscopic nature of the dark sector and its dark matter content. For example, dark matter with sizable self interactions and / or dissipation can leave distinctive signatures on the properties of satellite galaxies around Milky Way-like hosts. In a recent study, I placed novel constraints on a generic class of self-interacting dark matter models by analyzing a number of Milky Way dwarf galaxies. The results push these models into a parameter space with a very specific and new prediction: self-interactions within satellite galaxies can be either very large (so large that new dynamical effects become important), or very small (so small that such models are usually thought of as collisionless), but not intermediate. Specifically, if self-interactions are large, some dwarfs of the Milky Way must be undergoing a process of gravothermal collapse, and this process has a number of distinct observational predictions which can be searched for in current and upcoming data. The same models predict dissipation in certain regions of the parameter space; this offers additional observable signatures. In this talk, I will lay out a program to fully cover the parameter space of such models within the next few years by utilizing new theoretical understanding as well as upcoming observational data.

*Dr Slone is a candidate for a position in the department

- Avital Dery, Cornell
Avital Dery, Cornell
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We propose a novel way to challenge the boundaries of our knowledge of particle physics. The Standard Model of particle physics is a tremendously successful framework that is known without doubt to be incomplete. It fails to explain central phenomena such as neutrino masses, dark matter, and the baryon asymmetry of the universe. In order to tackle the question of what is the more fundamental Lagrangian describing the particle content of the universe, New Physics is being searched for in a variety of ways, from particle accelerators to astrophysical observatories.

I will discuss recent progress in the "intensity frontier", and demonstrate how careful analysis of rare processes at low energies is potentially sensitive to physics at scales that far exceed the reach of present day particle colliders. I will review our proposal for a next-generation multi-purpose kaon experiment with the potential to (i) test less explored sectors of the SM, (ii) look for new particles and interactions, and (iii) study aspects of the strong interaction.

* Dr Dery is a candidate for a position in the department

*** Note unusual date and time ***

- Nir Mandelker, HUJI
Nir Mandelker, HUJI
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Gas accretion onto galaxies is perhaps the most fundamental process driving their evolution, supplying fuel for star-formation, setting the angular momentum and size of disk galaxies, and driving turbulence and disk instabilities. Over the last two decades, a coherent picture has emerged whereby gas is accreted onto dark matter halos from the intergalactic medium (IGM) primarily in a smooth flow along filaments and sheets comprising the cosmic web of large-scale structure, rather than through mergers. During cosmic-noon, at redshifts z~(2-6) near the peak of cosmic structure-formation, intergalactic filaments manifest as narrow streams of cold gas (T~10^4 K) that feed galaxies directly from the cosmic web, penetrating their dark matter haloes and free-falling to the central disk, even in massive halos filled with hot gas (T>~10^6 K) with cooling times of order the Hubble time. However, the thermal, morphological, and kinematic properties of gas that eventually reaches the galaxy – setting disk size, spin, and turbulence – depend sensitively on how streams interact with the circumgalactic medium (CGM) of gas within DM haloes.  We therefore cannot understand galaxy evolution without a detailed understanding of accretion, and we cannot understand accretion without a detailed understanding of the multiphase C/IGM and its interaction with cold streams.
I will present the latest results from a systematic study of this interaction, using a combination of analytic models, idealized high-resolution numerical simulations, and cosmological simulations. We study the effects of hydrodynamics, radiative cooling, self-gravity, the halo potential, and magnetic fields, separately and in tandem, in order to gain insight into stream evolution in different limits. We find that while hydrodynamic instabilities can disrupt streams in the CGM, these are stabilized by cooling, gravity, and MHD. Radiative cooling in the turbulent mixing layer between the stream and the CGM is observable in Lyman alpha, and can explain several observed Lyman alpha blobs. Self-gravity in the streams can lead to star-formation in the CGM at redshifts z > 4. MHD leads to magnetically dominated interface regions which appear out of thermal pressure equilibrium and impact the phase structure of the high-z CGM. Finally, I will discuss how the streams that eventually reach the central galaxy can efficiently drive turbulence in galactic disks, leading to the violent disk instability observed at high-z.
- Banibrata Mukhopadhyay, Indian Institute of Science (IISC)
Banibrata Mukhopadhyay, Indian Institute of Science (IISC)
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Importance of magnetic fields and gravitational effects, particularly the general relativistic one, is already understood to play key roles in many modern astrophysical processes including underlying gas dynamics. However, in certain features lying with the detection of black holes and white dwarfs, the combined effect of magnetic fields and general relativity appears to be indispensable. They are powerful jets in a black hole accretion disk, ultra-luminous X-ray sources in their hard states, super-Chandrasekhar limiting mass white dwarfs to explain extremely over-luminous type Ia supernovae significantly violating the Chandrasekhar-limit and Philips relation, massive neutron stars predicted by gravitational wave astronomy etc. I will attempt to uncover the key features of the combined magnetic and general relativistic effects, explaining the above stated enigmatic sources observationally.

This talk will be given remotely over Zoom, at https://zoom.us/j/9290951953

The time is 14:00 Israel Time, 17:30 India Standard Time

- Shany Danieli, Princeton University
Shany Danieli, Princeton University
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The number densities, structures, and internal dynamics of low-mass galaxies provide some of the most interesting clues to the nature of dark matter and the theory of galaxy formation on small scales. Up until recently, our understanding of low-mass galaxies has largely been informed by observations of dwarf galaxies that orbit our Milky Way galaxy. I will present novel observational efforts that now enable the discovery of such low surface brightness galaxies beyond our local galactic neighborhood. I will discuss some of the follow-up observations of these extragalactic low-mass galaxies, focusing on their dark matter content and intriguing globular cluster populations, revealing significant diversity and new astrophysical puzzles. I will conclude by discussing ongoing surveys that will be essential in mapping the census and properties of the general population of low-mass galaxies.

- Julian Westerweck, Albert Einstein Institute (AEI), Hannover, Germany
Julian Westerweck, Albert Einstein Institute (AEI), Hannover, Germany
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When two black holes merge, the late stage of gravitational wave emission is a superposition of exponentially damped sinusoids. According to the black hole no-hair theorem, this ringdown spectrum depends only on the mass and angular momentum of the final black hole. An observation of more than one ringdown mode can test this fundamental prediction of general relativity. Here we provide strong observational evidence for a multimode black hole ringdown spectrum using the gravitational wave event GW190521, with a Bayes factor of 56 preferring two fundamental modes over one. The dominant mode is the l=m=2 harmonic, and the sub-dominant mode corresponds to the l=m=3 harmonic. We present an extensive study of simulated signal injections that confidently supports the statistical evidence. Two methods are employed to search for quasi-normal modes in the data, using signal models that are agnostic or assuming the Kerr solution for the black hole. Analysing the statistical properties of these methods in detail for signals similar to GW190521, we find they perform robustly and effectively in distinguishing the presence of multiple quasi-normal modes from noise. We also find that simulated GW190521-like signals with a (3, 3, 0) mode present yield tight  constraints on deviations of that mode from Kerr, whereas constraints on the (2, 2, 1) overtone of the dominant mode yield wide constraints that are not consistent with Kerr. These results on simulated signals are similar to what we find for GW190521. Applying our methods to GW190521, we estimate the redshifted mass and dimensionless spin of the final black hole as ~328 solar masses and ~0.86, respectively. The detection of the two modes disfavours an equal-mass binary; the mass ratio is constrained to 0.4 (+0.2−0.3). We find that the final black hole is consistent with the no-hair theorem and constrain the fractional deviation from general relativity of the sub-dominant mode’s frequency to be −0.008 (+0.08−0.09).

- Paz Biniamini, ARCO, Open University
Paz Biniamini, ARCO, Open University
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The interaction of Fast Radio Burst (FRB) radio waves with the intervening plasma between us and the sources is viewed, at times, as a nuisance for probing intrinsic FRB properties. At the same time, it offers unique ways to probe interstellar matter at large redshifts and the intervening intergalactic medium. I will show that FRBs are a promising and unique tool for exploring the H reionization history of the Universe. In addition, due to multi-path propagation, a magnetized plasma screen can cause temporal broadening of the FRB, lightcurve variability, spectral decoherence, depolarization, induced circular polarization and image broadening. I will describe how these different properties are directly inter-related, how they manifest in FRB and pulsar observations, how this can already be used to constrain the nature of the intervening plasma in some bursts and how it affects lensing prospects of FRBs.

- David Bermudez, Center for Research and Advanced Studies Mexico City
David Bermudez, Center for Research and Advanced Studies Mexico City
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Hawking radiation is usually defined as radiation expected to be emitted by the event horizon of black holes. This radiation originates from the interaction of the quantum field on the classical background of the curved spacetime around the black hole. This effect is often considered a reliable prediction although it has not been detected and it relies on some dubious assumptions. However, it is possible to view this effect in a more general way. What is a black hole? What are the necessary ingredients to create Hawking radiation? What if instead of gravity we use a different interaction to create a curvature? What type of horizon is necessary? What is the role of negative frequencies in the phenomenon? All these questions are answered by a relatively new and small field of study known as analogue gravity, where effects usually related to gravity are studied in other systems. The most successful ones so far are water tanks, Bose-Einstein condensate, and light pulses in dielectrics. In this talk, we will discuss these topics to lead to a broader understanding of their details, we will present in depth the optical analogues, and we will discuss recent theoretical and numerical results of our research group, as well as some experimental ones in collaboration with laboratories from Mexico and Israel.

Note exceptional day and location: Sunday at Reznick.

Dr. Bermudez is a candidate for a position in the department.

- David Benisty, DAMTP, Cambridge, UK
David Benisty, DAMTP, Cambridge, UK
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The General Theory of Relativity needs at least one modification - the Cosmological Constant. Yet there are possibilities for other modified theories of gravity to explain the accelerated expansion. In this talk I'm going to discuss the impact of Modified Gravity on the two-body problem. In particular, with the latest observational constraints from the galactic center, binary pulsars and the Milky and Andromeda dynamics.

Dr Benisty is a candidate for a position in the department

- Olga Khabarova, IZMIRAN, Russian Academy of Sciences
Olga Khabarova, IZMIRAN, Russian Academy of Sciences
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Magnetic reconnection is known to transform the magnetic energy into other forms of energy in laboratory and space plasmas. Solar physics and physics of the terrestrial magnetosphere consider this mechanism as the main candidate for acceleration of charged particles to suprathermal energies at reconnecting current sheets. It took scientists several decades to make the way from imaging magnetic reconnection as the simplest Petschek or Sweet-Parker mechanism operating at Harris-type current sheets to understanding this as a 3D turbulent/intermittent/stochastic process associated with creation of flux ropes, secondary current sheets and waves. Studies of magnetic reconnection in the solar wind were far less easy than those in the magnetosphere, first of all, because of the insufficiency of data from spacecraft and the absence of multi-point observations in the heliosphere. As a result, the views on the subject developed in the same way as in magnetospheric physics but it took us longer to realize some critical points about the complexity of magnetic reconnection in heliospheric plasmas. Furthermore, the idea of local particle acceleration by magnetic reconnection in the solar wind has been denied for a long time, and the situation shifted toward its acceptance only during the last decade. Historical and modern views on magnetic reconnection and local particle acceleration in the heliosphere will be discussed in the presentation, with a focus on observations from past and recent heliospheric missions at different distances from the Sun.

Dr. Khabarova is a candidate for a position in the department

- Allona Vazan, ARCO (Astro Research Center at the Open University)
Allona Vazan, ARCO (Astro Research Center at the Open University)
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The discoveries of thousands of extrasolar planets in our galaxy raise fundamental questions about formation, composition and interior structure of planets. In traditional models of planetary interiors the planets are structured in 2-4 distinct layers of different composition (iron, rock, water, gas), similar to the Earth. However, new theoretical and observational evidence suggest that in general planetary interiors may be very different from this simplified picture. I will show some of these new findings and discuss how we expect planetary interiors to look, based on recent planet formation and evolution models.

- Ayala Glick Magid, Hebrew University of Jerusalem, Israel
Ayala Glick Magid, Hebrew University of Jerusalem, Israel
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The Standard Model (SM) of particle physics describes all known elementary particles and fundamental forces, excluding gravity. There is, however, growing evidence that the Standard Model is incomplete. Recent years have seen an extensive effort put into finding evidence for interactions beyond the Standard Model (BSM) of physics, making use of precision measurements of nuclear beta-decays in different nuclei. To identify these BSM signatures, experimental measurements must be compared with accurate theoretical predictions. In this talk, I will introduce this experimental surge, motivating me to develop the theoretical formalism required for the analysis of experiments currently being conducted. Presenting a new approach for decomposing tensor interactions of fermionic probes within the multipole analysis, I will examine how signatures of new physics appear in the correlations between the particles emitted in β-decays, and in the energy spectrum of allowed and forbidden decays, which I will show that have an increased sensitivity to these signatures. In addition, to be able to distinguish between new physics signatures and high orders of the known SM physics, I will describe a general framework, suitable for any nucleus and any decay, enabling precise calculations of β-decay observables required for ongoing experiments, with controlled accuracy, evaluated by identifying a hierarchy of small parameters related to the low momentum transfer that characterizes β-decays. First applications to 6He and 23Ne β-decay ongoing measurements at the SARAF accelerator, Israel, will be presented, resulting in new constraints on BSM tensor interactions, and paving the way for new, even more accurate, experiments and discoveries.

- Victor Chernov, Ort Braude
Victor Chernov, Ort Braude
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The James Webb Telescope has been launched to space using an Ariane 5 rocket. The telescope that promises a leap in our understanding of the universe weighs 6.5 metric tons and is be located at the Lagrange L2 point, 1.5 million km from Earth. How do we deliver something so big so far? We burn hundreds of thousands of kilograms of hydrogen and oxygen.

Combustion is one of the oldest technologies of mankind. The use of fire probably began before the advent of Homo Sapiens, and it is still the main source of energy today. We use combustion for heating, generating electricity, propelling vehicles on land, sea, air and space, and more. The widespread use of combustion has created many opportunities but has also led to many problems.

In this seminar we’ll review the basic principles of combustion and its selected uses will be offered - from heating homes to space flights. Modern challenges of the field will be discussed. A speculation regarding the future of combustion will be presented. No demonstrations are expected due to safety regulations.

About the presenter: Victor is a Senior Lecturer at the Department of Mechanical Engineering, ORT Braude College of Engineering. He holds a Ph.D. in Aerospace Engineering and specializes in rocket propulsion, combustion and fluid mechanics.

- Noa Zilberman, Technion
Noa Zilberman, Technion
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Astrophysical black holes are known to be rotating. The simplest spacetime solution describing a classical rotating black hole (the Kerr solution) reveals a non-trivial spacetime structure, in which the geometry connects through an inner horizon to another external universe. But does such a traversable passage really exist inside a physically-realistic spinning black hole?

Answering this question, along others, requires one to understand the manner in which quantum energy fluxes affect the internal geometry of a black hole. It has been widely anticipated, yet inconclusive (till this work), that semiclassical effects would diverge at the inner horizon of a spinning black hole. Such a divergence, if indeed takes place, may drastically affect the internal black hole geometry, potentially preventing the inner horizon traversability. Clarifying this issue requires the computation of the quantum energy fluxes in black hole interiors. However, this has been a serious challenge for decades.

Using a combination of new and old methods, we have recently managed to compute the semiclassical energy fluxes at the inner horizon of a spinning black hole, in a vacuum state corresponding to an evaporating black hole. We found that these fluxes are either positive or negative, depending on the black hole spin (and polar angle). The sign of these fluxes may be crucial to the nature of their backreaction on the geometry (as should be dictated by the semiclassical Einstein equation).

In this talk, we shall describe the basic framework of semiclassical general relativity and the regularization procedure, and then present our novel results for the semiclassical fluxes at the inner horizon of a rotating black hole, briefly mentioning possible implications for the inner horizon traversability.

- Elena Kantor, Ioffe Physical-Technical Institute of the Russian Academy of Sciences
Elena Kantor, Ioffe Physical-Technical Institute of the Russian Academy of Sciences
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An increasing amount of observational data provides us with more and more manifestations of neutron star (NS) oscillations. To interpret existing and future observations one needs to develop adequate models of oscillating NSs. Such models have to account for baryon pairing in stellar interiors. In my talk I will first discuss some general characteristics of oscillation modes in superfluid NSs, their spectra and dissipation timescales. I will then present some more details about two specific classes of oscillations called g-modes, which might excite resonantly during the neutron star inspirals, and about r-modes, which can serve as a powerful tool to probe the properties of superdense matter. Finally, I will consider possible imprints of superfluid oscillation modes in gravitational wave signal from neutron star inspirals.

- Mikhail Gusakov, Ioffe Physical-Technical Institute of the Russian Academy of Sciences
Mikhail Gusakov, Ioffe Physical-Technical Institute of the Russian Academy of Sciences
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In order to correctly interpret observations of neutron stars (NSs) and constrain the properties of
superdense matter, it is necessary to have an adequate theory describing the large-scale NS
dynamics. In the first part of the talk I will discuss the key ingredient of such a theory, the
superfluidity of nucleons in the inner layers of NSs, as well as the corresponding
(magneto)hydrodynamic equations. In the second part of the talk, I will briefly review several
possible methods for studying the internal structure of NSs and discuss some problems and

- Karamveer Kaur, Hebrew University of Jerusalem
Karamveer Kaur, Hebrew University of Jerusalem
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Some dwarf galaxies like Fornax dwarf Sph containing old globular clusters pose an interesting timing puzzle. The dynamical friction timescales ~ a few Gyrs calculated from the Chandrasekhar formula based on a local theory are too short and imply that these globulars should have already sunk to the center of the host galaxy. This timing problem was solved by N-body simulations which suggest suppression of dynamical friction in cored density profiles of the host. The local theory can not capture this effect and we explore this problem with Tremaine-Weinberg theory which is a global approach and takes into account the real orbital structure of the host galaxy. In this linear response theory, the dynamical friction acts via resonant interactions between perturber and background stars. We show that the number and strength of resonances are reduced inside the core which leads to a suppressed dynamical friction and stalls the evolution of perturber's orbit away from the galaxy center (commonly called "core stalling"). We further explore the density wakes of perturber and find interesting geometrical transformations associated with core stalling.

This talk will be based on these papers:

https://arxiv.org/abs/2112.10801

https://arxiv.org/abs/1810.00369

- Naama Hallakoun, Weizmann Institute of Sciecne
Naama Hallakoun, Weizmann Institute of Sciecne
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The characterization of the double white dwarf (DWD) population is crucial to our understanding of multiple questions, from stellar evolution, through the progenitors of Type-Ia supernovae (SNe Ia), to gravitational-wave (GW) sources. In this talk I will discuss the current status of the observed DWD population and the future prospects for the upcoming GW observations with the Laser Interferometer Space Antenna (LISA).

First, I will present a statistical analysis of the local DWD population using two large, multi-epoch, spectroscopic samples: SDSS (Badenes & Maoz 2012), and SPY (Maoz & Hallakoun 2017). By combining the results from these complementary samples, more precise information on the DWD population and on its (GW-driven) merger rate can be obtained (Maoz, Hallakoun, & Badenes 2018), indicating that about 10% of the WDs are in DWD systems with separations ≤4 AU. The implied Galactic WD merger rate is ∼1e-11 per year per WD, which is 4.5-7 times higher than the Milky Way's specific SN Ia rate.

Next, I will show how we used these results to predict the number and the properties of DWDs detectable by LISA (Korol, Hallakoun, Toonen, & Karnesis 2022). We find that the observationally driven estimates yield 2-5 times more individually detectable DWDs than various binary population synthesis forecasts, and a significantly different shape of the DWD confusion foreground. Both results have important implications for the LISA mission.
- Caner Unal, Ben Gurion University
Caner Unal, Ben Gurion University
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In the first part of the talk, I will discuss PBH formation, accompanying density induced GWs and probing small scales of inflation. Also I will discuss stellar mass, asteroid mass and super massive BH mass range and their possible interesting implications for cosmology. I will also discuss how we can probe PBHs conclusively via multi messengers (pulsar-time arrays and CMB distortions). In the second part, I will discuss the Fundamental Plane of BH activity (correlation of radio and Xray radiation) and its spin modification, ie the spin influence on accretion and jet processes. I will finally discuss,  we can derive spin bounds for quasars and these spin values could be used to probe/derive bounds for ultra light boson properties via superradiance such as mass, self-interaction and energy density.

- Sir Roger Penrose, Oxford
Sir Roger Penrose, Oxford
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This week's Astro Seminar is replaced by the annual Bekenstein Memorial Lecture in Fundamental Physics, this year by 2020 Nobel Laureate Roger Penrose (Oxford). The lecture is organized by the Israel Physics Colloquium (IPC) and by the Racah Institute of the Hebew University (HUJI).

- Ira Wolfson, SISSA
Ira Wolfson, SISSA
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Title: Limits on perturbative treatment for inflationary potentials and what does it mean for the next stage of precision cosmology.

In this talk we briefly discuss the notion of slow-roll inflation, and the mechanism with which it creates the structure of the observed universe. We outline the problem of inferring inflationary potentials from the shape of the primordial power spectrum (PPS), which in itself is a statistical inference from the shape of the matter power spectrum.

We then present some of the methods and heuristics used in building models of inflation, and show that in the age of precision cosmology, they are insufficient. We argue that our current employed statistical and theoretical methods effectively smooth over features in the PPS, which may be crucial for our understanding of high energy physics.

Finally, we comment on the confidence limits of the theoretical methods in model building, and argue that for some classes of inflationary models, no analytic approximation using the current tools may be feasible.

This talk is based on arxiv:2110.10557

Note: Ira is a candidate for the department. Anyone interested in meeting with him can mark themselves here:

- Sivan Ginzburg, CalTech
Sivan Ginzburg, CalTech
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The vast majority of detected planets are observed indirectly, using their small perturbation on the light emitted by the host stars. In recent years, however, the world's largest ground based telescopes have succeeded in directly imaging the light coming from some planets themselves. I will present our comprehensive theory for the mass, luminosity, and spin of gas giant planets during their final stages of formation - when they simultaneously contract and accrete gas from a disk. I will apply this theory to the luminosity and spectrum obtained by the novel direct-imaging technique, highlighting the recently discovered PDS 70 system, where two planets were directly observed during formation for the first time.

Note: The seminar will be given *on campus*, and Sivan will be available for discussions during the day for anyone interested. Anyone interested in speaking with him is invited to register for a slot here: https://docs.google.com/spreadsheets/d/1o-xN-B27a_htzTMo-dwdfMmX4mzWfGg…

- Uri Kol
Uri Kol
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Black holes are characterized by four externally observable classical parameters: mass, angular momentum, electric and magnetic charges. Recent studies showed that this standard picture is incomplete and that black holes are also characterized by an additional new property - the "magnetic-mass" (or "dual-mass"). The discovery of the magnetic-mass revealed, in turn, a brand new mathematical structure in General Relativity as well as novel observational signatures that I will discuss in detail.

Note: Uri is a candidate for the department. Anyone interested in speaking with him is invited to register for a slot here: https://docs.google.com/spreadsheets/d/1KATnuOMVFMd3kUxxTpiNJhJYWZnZSSY…

Due to new COVID-related travel restrictions, the seminar will be given over Zoom

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The universal law of gravitation has undergone stringent tests for many decades over a significant range of length scales, from atomic to planetary. Of particular interest is the short distance regime, where modifications to Newtonian gravity may arise from axion-like particles or extra dimensions. We have constructed an ultra-sensitive force sensor based on optically-levitated microspheres with a force sensitivity of 10^(−16)N/√Hz to investigate non-Newtonian forces that couple to mass with a characteristic scale of ∼ 10μm. In this talk, I will present the first investigation of the inverse-square law using an optically levitated test mass, along with the technical development that preceded it.

In addition, I will present another precision measurement conducted with the same setup aiming to determine if the charge of the proton is equal in magnitude to the charge of the neutron. This equality has been tested with great precision over the last century and has supporting arguments from the theory side. However, this measurement is a sensitive tool to probe new physics as it is breaking down in a few suggested extensions of the standard model.

Nadav is a candidate for the department; anyone interested in meeting in person for discussions, may fill in the schedule here: https://docs.google.com/spreadsheets/d/1o-xN-B27a_htzTMo-dwdfMmX4mzWfGg…

- Shmuel Bialy, University of Maryland
Shmuel Bialy, University of Maryland
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Stars form in interstellar clouds through gravitational collapse. To remain gravitationally unstable, the clouds need to efficiently lose energy, which they do through radiative cooling. Once the stars form, they begin injecting energy back into the interstellar medium, which regulates the next-generation star-formation process. In this talk, I will review key aspects of this feedback process, focusing on the interaction of supernovae, cosmic-rays, and far-UV radiation with interstellar clouds.

I will discuss our recent discovery of the "Per-Tau Shell", a gigantic 3D shell of gas and dust in the solar vicinity, that is actively forming new stars. This provides the first 3D observational evidence for the constructive aspect of supernovae, where instead of destroying clouds, supernovae promote cloud condensation and trigger the formation of a new generation of stars.

Supernovae are also the dominant sites of acceleration of cosmic rays. I will discuss a new way for constraining the proton cosmic-ray interstellar spectrum at low energies (E<GeV), which is currently highly uncertain. The James Webb Space Telescope will be a key player in this quest, shedding new light on the generation and propagation of low-energy cosmic rays.

Shmuel is a candidate for the department.

Note unusual date (Wednesday), because Tuesday is 10th Tevet. The seminar will be *only* on Zoom (meeting id 9290951953) - at 17:00 Jerusalem Time.

- Ido Ben Dayan, Ariel / University of California at Berkeley
Ido Ben Dayan, Ariel / University of California at Berkeley
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The Concordance Model of Cosmology describes the Universe on large scales and its parameters have been measured to an accuracy of a percent.

I will discuss current challenges of the model and attempts to address them.

Emphasis will be given to the role emergent collective phenomena beyond a single scalar field may have in the early and late Universe.

As an application I will show that the thermal average of "unparticles" can avoid the Big Bang singularity, act as a Dark Energy model and reduce the Hubble tension.

Note: This seminar will be given *only* on Zoom (meeting id 9290951953), from sunny California.

- Lev Tal Or, Ariel
Lev Tal Or, Ariel
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CARMENES is a radial-velocity (RV) survey for exoplanets around nearby M dwarf stars. Using a high-resolution dual-channel spectrograph, it provides M-star RV measurements with a precision down to ~1 m/s. In five years of surveying ~300 nearby M-dwarfs, we have detected ~30 new planets, including habitable-zone Earth-mass planets (Teegarden’s Star b&c) and planets that challenge planet-formation models. Some of the new planets are amenable for characterization by next-decade direct-imaging and astrometric instruments. In addition, CARMENES was used to estimate the masses of ~12 transiting planets around nearby M dwarfs, including AU Mic b&c. CARMENES’ unique design allows addressing additional questions related to M dwarfs and close-in planets, such as the spectroscopic manifestation of photospheric activity and rotation, magnetic field strength of active stars, and the atmospheric composition of hot massive planets. In the talk, I will give a brief overview of the latest results from CARMENES and an outlook to its future.

- Nora Linn Strotjohann, Weizmann Institute of Science
Nora Linn Strotjohann, Weizmann Institute of Science
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Interaction-powered supernovae (SNe) explode within an optically thick circumstellar medium (CSM) that could be ejected during eruptive events. To identify and characterize such pre-explosion outbursts, we produce forced-photometry light curves for 196 interacting SNe, mostly of Type IIn, detected by the Zwicky Transient Facility between early 2018 and 2020 June. Extensive tests demonstrate that we only expect a few false detections among the 70,000 analyzed pre-explosion images after applying quality cuts and bias corrections. We detect precursor eruptions prior to 18 Type IIn SNe and prior to the Type Ibn SN 2019uo. Precursors become brighter and more frequent in the last months before the SN and month-long outbursts brighter than magnitude −13 occur prior to 25% (5–69%, 95% confidence range) of all Type IIn SNe within the final three months before the explosion. With radiative energies of up to 1049 erg, precursors could eject  ∼1 M ⊙ of material. Nevertheless, SNe with detected precursors are not significantly more luminous than other SNe IIn, and the characteristic narrow hydrogen lines in their spectra typically originate from earlier, undetected mass-loss events. The long precursor durations require ongoing energy injection, and they could, for example, be powered by interaction or by a continuum-driven wind. Instabilities during the neon- and oxygen-burning phases are predicted to launch precursors in the final years to months before the explosion; however, the brightest precursor is 100 times more energetic than anticipated.

- Shahar Hadar, Oranim (Haifa University)
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The region of spacetime near the event horizon of a black hole can be viewed as a deep potential well at large gravitational redshift relative to distant observers. However, matter orbiting in this region travels at relativistic speeds and can impart a significant Doppler shift to its electromagnetic emission, sometimes resulting in a net observed blueshift at infinity. Thus, a black hole broadens the line emission from monochromatic sources in its vicinity into a smoothly decaying “red wing”—whose flux vanishes at large redshift—together with a “blue blade” that retains finite flux up to a sharp edge corresponding to the maximum observable blueshift. In the talk, I will describe the blue blade produced by isotropic monochromatic emitters on circular equatorial orbits around a Kerr black hole, and outline how the maximum blueshift simply encodes black hole spin and inclination. These results bear direct relevance to ongoing and future observations aiming to infer the angular momenta of supermassive black holes from the broadening of their surrounding line emission.

Meir Shimon, Tel-Aviv University
Meir Shimon, Tel-Aviv University

The standard cosmological model, which is firmly based on General Relativity (GR), has been very successful in parametrically fitting diverse combinations of observational datasets. This success rests on the stipulated existence of dark matter (DM) and dark energy, both of which remain elusive. In addition, the model heralds the breakdown of our basic concepts of space and time at the initial Big Bang singularity.

In this talk I will argue that extending the symmetry of GR to accommodate Weyl-invariance (WI), i.e. allowing for our fundamental measure sticks, such as the Planck length, to vary in space and time could potentially obviate the need for clustering DM on all scales, avoid the initial singularity problem with a bouncing model of the Universe, and resolve several other puzzles afflicting the standard cosmological model.

Note: Meir is a candidate for the department

- Almog Yalinewich, Canadian Institute for Theoretical Astrophysics, Toronto
Almog Yalinewich, Canadian Institute for Theoretical Astrophysics, Toronto
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When massive stars exhaust their nuclear fuel, their core collapses to form a compact object, releasing a large amount of energy and giving rise to an outward moving shock wave. If this shock wave is able to overcome gravity, the star explodes and produces a transient called a supernova. If, instead, gravity overwhelms the shock wave, then the star collapses directly to a black hole. In this talk I will discuss my research of the passage of this shock wave inside the interior of the star. I will focus on two extremes: the behaviour close to the centre of the star (the explosion mechanism) and near the stellar surface (shock breakout). I will show how results from this study, with the data from upcoming missions, can shed light on the properties of the progenitor star and the outcome of the star’s death (whether it explodes or not, and what kind of object it leaves behind). I will also discuss how insights from this study can be used to model other violent astrophysical processes.

Note: the seminar will be given remotely over Zoom, on https://zoom.us/j/9290951953

- Gunnar Markus Riemenschneider, Universita di Torino
Gunnar Markus Riemenschneider, Universita di Torino
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Faithful, robust and fast waveform models are of critical importance to gravitational wave (GW) astronomy to allow for accurate and precise detection and analysis of the source. Waveform models based on the Effective-One-Body (EOB) approach have been proven to be very powerful in their ability to combine analytical information from PN theory, gravitational-self-force theory and more, in order to capture the full picture of merging binary systems. Purely analytical EOB models are however still of insufficient quality to be used in the detection and analysis of GW events. This thesis presents an introduction to the solution of this problem: The completion of EOB waveform models through Numerical Relativity (NR), on the example of non-precessing, non-eccentric Binary Black Hole (BBH) systems, utilizing the framework of the TEOB model. Once completed NR is further used to validate the model to ensure it meets the qualitative needs of GW data analysis.

The infrastructure of the TEOB model is introduced and discussed with a strong focus onto analytical flexibilities that can be used to capture missing information from NR waveforms. The analytical flexibilities of the TEOB model are made up of effective parameters that enter the Hamiltonian so as to modify both the orbital part (i.e.~non-spinning) and the spin-orbit interaction between the orbital angular momentum and the black hole spins. The approximation of a quasi-circular inspiral is corrected effectively in the radiation reaction of the system by imposing NR fitted waveform characteristics. The model is completed with a phenomenological template fitted directly to NR to capture the merger and ringdown of the BBH system. In total 154 BBH-NR waveforms are combined to inform the TEOB. An additional 460 waveforms are used to validate the model. These waveforms span over a large part of the parameter space reaching mass-ratios $m_1/m_2\leq 18$ and black hole spins of up to $|\vec{S}_{1,2}|/m^2_{1,2} \leq 0.998$. This calibration process is presented for three, successively improving avatars of the TEOB model. The TEOB avatars discussed in this thesis are: Firstly, TEOBResumS is a model for the dominant, quadrupolar mode; Secondly, TEOBiResum_SM models BBH systems of non-rotating black holes, extending the calibration of the quadrupolar mode to a large set of 9 further subdominant modes; Finally, TEOBiResumS_SM extends the calibration of all but one subdominant mode to the full spin-range available of available NR waveforms. The fully calibrated models are all evaluated against the NR catalog. In many instances the model does not just meet but exceeds the quality demands for application in GW astronomy.

The talk will be given on Zoom: https://zoom.us/j/9290951953 at 17:00 Israel Time (16:00 CEST).

- Daniel Wysocki, University of Wisconsin–Milwaukee / CGCA
Daniel Wysocki, University of Wisconsin–Milwaukee / CGCA
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With the release of the second Gravitational Wave Transient Catalog (GWTC-2), there are now nearly 50 confident compact binary mergers detected by the LIGO and Virgo instruments.  This includes multiple detections consistent with the presence of a neutron star.  Whereas the first such detection, GW170817, was confirmed to contain at least one neutron star by its electromagnetic counterpart, none of these new candidates have counterparts to aid their classification.  GW190814 is of particularly ambiguous origins, as its smaller compact object (2.50-2.67 solar masses at the 90% credible level) is either the largest known neutron star, or the smallest known black hole.

While most previous population studies focus in on a single source category (most frequently binary black holes), the presence of at least one ambiguous event makes it necessary to simultaneously fit all three source categories (binary black holes, binary neutron stars, and neutron star-black hole binaries).  In this talk I will discuss several recent analyses which do precisely this.  I also apply the same techniques to identify subpopulations within the broader binary black hole population.

- Meir Shimon, Tel-Aviv University
Meir Shimon, Tel-Aviv University
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The apparent missing mass in galaxies and galaxy clusters, commonly viewed as evidence for dark matter, could possibly originate from gradients in the gravitational coupling parameter, $G$, and active gravitational mass, $M_{act}$, rather than hypothetical beyond-the-standard-model particles. We argue that in (the weak field limit of) a Weyl-invariant extension of General Relativity, one can simply affect the change $\Phi_{b}(x)\rightarrow\Phi_{b}(x) + \Phi_{DM}(x)$, where $\Phi_{b}$ is the baryon-sourced potential and $\Phi_{DM}$ is the `excess' potential. This is compensated by gradients of $GM_{act}$ and a fractional increase of $O(-4\Phi_{DM}(x))$ in the baryon density, well below current detection thresholds on all relevant scales.

- Alex Nielsen, Stavanger University (Norway)
Alex Nielsen, Stavanger University (Norway)
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Evidence for echo signals from black holes would be a phenomenal indication of new physics beyond standard gravitational models. I will discuss some of the wide range of tests that have been performed to date on gravitational wave data and discuss some of the theoretical and observational challenges as we go forwards.

- Barak Kol, Hebrew University of Jerusalem, Israel (HUJI)
Barak Kol, Hebrew University of Jerusalem, Israel (HUJI)
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The three-body problem in Newtonian gravity is one of the oldest and richest problems in physics. Giants have worked on it and it has been the source of numerous fields in theoretical physics and mathematics including perturbation theory, topology and chaos. Yet, it remains unsolved, and the associated statistical theory remains incomplete and flawed even after almost fifty years of work. Inspired by recent beautiful work of Nick Stone and his collaborator Leigh, I have developed a reduction of the outcome probability distribution. In this sense, I believe the problem has been cracked, as will described in the talk.

The talk is based on https://arxiv.org/abs/2002.11496

- Yoshinta Setyawati, Max-Planck-Institut für Gravitationsphysik (Utrecht University & Albert-Einstein-Institut)
Yoshinta Setyawati, Max-Planck-Institut für Gravitationsphysik (Utrecht University & Albert-Einstein-Institut)
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Fast and accurate binary-black-hole (BBH) merger waveform models that span wide parameter ranges are crucial for future searches and parameter estimation of gravitational-wave data. To date, analytical waveforms that incorporate numerical-relativity information, such as effective-one-body and phenomenological models, play an important role in analysing LIGO and Virgo data. However, these models are not automatically updated every time new numerical waveforms become available. Here we present a new perspective on dynamically tuning waveform models by incorporating sparse information from a more accurate model. We also show the first attempts to use our method to include additional physical effects that were not present in the original model and investigate various techniques that include interpolation and regression implemented in the development of waveform modeling.

The talk will be given over Zoom, at https://zoom.us/j/9290951953

- Vassilios Mewes, Oak Ridge National Lab
Vassilios Mewes, Oak Ridge National Lab
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Vassilios Mewes

National Center for Computational Sciences and Physics Division, Oak Ridge National Laboratory

The new era of gravitational wave multi-messenger astrophysics began with the recent detection of the binary neutron star merger GW170817. Our theoretical understanding of these systems relies on high fidelity numerical relativity simulations including general relativistic magnetohydrodynamics, realistic equations of state for matter up to nuclear densities, and neutrino radiation hydrodynamics. The approximate symmetries of the post-merger stage of the evolution, namely hypermassive neutron stars and black hole torus systems, make spherical coordinates better suited than Cartesian coordinates for the numerical modelling of these systems. This seminar will present SphericalNR, a new framework within the publicly available Einstein Toolkit to numerically solve the Einstein field equations of general relativity coupled to the equations of general relativistic magnetohydrodynamics in spherical coordinates without symmetry assumptions. A description of a reference metric approach together with algorithmic details enabling the use of spherical coordinates in the originally Cartesian code base of the Einstein Toolkit will be presented, followed by a description of ongoing algorithmic and code development work regarding a double FFT filter with the aim to alleviate the extremely severe timestep restrictions when solving hyperbolic PDEs in spherical coordinates with high angular resolutions. The outlook will touch upon future development for SphericalNR, focusing on extending the multi-physics capabilities of the framework, as well as challenges for increasing the parallel efficiency of the code with a view on the upcoming exascale era of HPC.

- Uri Kol, New York University (NYU)
Uri Kol, New York University (NYU)
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In this talk I will describe a phenomenon akin to Electric-Magnetic duality in Einstein's gravity. I will show that a new type of "magnetic" dual gravitational charges generate redundant symmetry transformations which are not part of the standard group of diffeomorphisms. General Relativity is therefore shown to possess an additional gauge symmetry of the metric which reveals, in turn, a wide class of new IR phenomena.

- Grant Meadors, Los Alamos National Lab (LANL)
Grant Meadors, Los Alamos National Lab (LANL)
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Space weather affects life on Earth and in outer space. Human technologies are affected by coronal mass ejections and similar outbursts of solar activities. Accurate prediction of the solar wind and its polarity can help understand the Sun and its dynamic environment. The Wang-Sheeley-Arge (WSA) phenomenological model of the coronal magnetic field can estimate solar-wind speed and interplanetary magnetic field polarity in the inner heliosphere by using photospheric magnetic field maps. WSA has historically used two parameters, the source surface and interface radii, to tune its predictions. In this talk, I describe how our team used sequential Monte Carlo, also called particle filtering, in the assimilation of satellite data to adjust the values of these radii. Adaptive optimization, applied to week-long timescales across several months of historical data, yielded approximately double predictive performance. In addition to improved forecasts, this statistical study highlights challenges in parameter estimation for the nearest and most-observed solar-mass object: the Sun.

*Approved for Los Alamos Unlimited Release: LA-UR-21-21918.

- Swetha Bhagwat, La Sapienza University, Roma
Swetha Bhagwat, La Sapienza University, Roma
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In this talk I will talk about a recent work where we propose a new test of GR. The gravitational waves emitted during the coalescence of binary black holes offers an excellent probe to test the behaviour of strong gravity at different length scales. In this work, we propose a test called the merger-ringdown consistency test that focuses on probing horizon-scale dynamics of strong-gravity using the binary black hole ringdowns. This test is a modification of the more traditional inspiral-merger-ringdown consistency test. I will present a proof-of-concept study of this test using simulated binary black hole ringdowns embedded in the Einstein Telescope-like noise. Furthermore, we use a deep learning framework, setting a precedence for performing precision tests of gravity with neural networks.

The talk is at 17:00 Jerusalem Time (16:00 CET), on Zoom: https://zoom.us/j/9290951953

- Greg Ashton, Monash University & Royal Holloway, University of London
Greg Ashton, Monash University & Royal Holloway, University of London
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The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

- David Benisty, Ben Gurion University & Frankfurt Institute for Advanced Studies
David Benisty, Ben Gurion University & Frankfurt Institute for Advanced Studies
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From the assumption that the slow roll parameter ϵ has a Lorentzian form as a function of the e-folds number N, a successful model of a quintessential inflation is obtained, as succinctly studied in \cite{Benisty:2020xqm}. The form corresponds to the vacuum energy both in the inflationary and in the dark energy epochs and satisfies the condition to climb from small values of ϵ to 1 at the end of the inflationary epoch. We find the corresponding scalar Quintessential Inflationary potential with two flat regions. Moreover, a reheating mechanism is suggested with numerical estimation for the homogeneous evolution of the universe. The suggested mechanism is consistent with the BBN bound.

Based on: https://arxiv.org/abs/2006.04129

The talk will be given on Zoom:

We will meet about 30 minutes before the official start time for virtual mingling and informal chat

- Maayane Soumagnac
Maayane Soumagnac
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We have entered a golden age for studying astrophysical “transients” (short and violent astrophysical events). Recent advances in the field of large-scale, high-cadence astronomical surveys have provided unprecedentedly rich and diverse data sets and transient astronomy is said to have entered a “big data era”. I will give a short overview of several on-going and future instruments which are real « game-changers » in the field and will show how combining their assets, as well as using tools from  "data science" - involving high-performance computing and data mining - can lead to promising new science. I will then share recent results from the first UV survey of the early evolution of interacting supernovae and from mining twenty years of X-ray archival data in search for the shortest transients, including the elusive signatures of the mysterious supernova "shock breakout".

Note the unusual date/time (Wednesday morning).

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

- Yotam Sherf, Ben-Gurion University
Yotam Sherf, Ben-Gurion University
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In this talk, we discuss the exciting possibilities of exploring strong gravity with future GW observations. The properties of Black-Holes (BH) and exotic compact objects (ECOs) immersed in a tidal environment are discussed. In particular, we focus on the BH reaction and its induced quadrupole moment to an external tidal field. The no-Love number theorem for GR BHs is thoroughly reviewed and alternative explanations are suggested. Here, I'll present for the first time how simple quantum mechanical arguments support the existence of the Love number in quantum black-holes, moreover I'll show how the detection of these quantum induced effects is possible with future precision gravitational wave measurement.

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The start time is 17:00 Jerusalem time

- Uri Malamud, Technion
Uri Malamud, Technion
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Several billion years into the future, our Sun will break away from the main sequence. It would expand, turning into a giant star, eventually shedding its outer layers to become a white dwarf -- a perpetually fading remnant of its former glory. We will not be around to see this. Planet Earth will be engulfed in the process. In the outer Solar system, planets and minor planets will be baked by the intense radiation from the giant Star, becoming active as comets do. Their orbits will expand, and this would give rise to rich dynamical interactions. In the aftermath of this calamity, many surviving objects would be injected into tidal crossing orbits of our Sun's ultra-dense successor, the white dwarf. As they do, they will be violently and repeatedly ripped apart, breaking into their smallest constituent building blocks. While we cannot hope to glimpse our own future, nature has given us a unique
opportunity to triumphantly jubilate as we watch the demise of other, less fortunate exo-planetary systems. In my talk I would briefly discuss various topics related to white dwarf atmospheric pollution by exo-planetary remnants: focusing on the properties and chemistry of the polluters ; the formation of debris discs and compact accretion discs; and the growing number of recent discoveries of individual (disintegrating or intact) minor and major exo-planets observed in orbit of white dwarfs.

The talk will be give over Zoom, at https://zoom.us/j/9290951953

- Daniel Pook-Kolb, Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut)
Daniel Pook-Kolb, Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut)
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Marginally outer trapped surfaces (MOTSs) are the main tool in numerical relativity to infer properties of black holes in simulations of dynamical systems. In this talk, I will present results that show how we can understand a merger of two black holes in terms of the evolution of these MOTSs. This closes a gap in our understanding of binary-black-hole mergers and provides the quasilocal analog of the famous "pair-of-pants" picture of the event horizon of two merging black holes. In particular, we will encounter three new phenomena: (i) the merger of MOTSs, (ii) the formation of self-intersecting MOTSs immediately after this merger, and (iii) a non-monotonicity result for the area of certain smoothly evolving MOTSs. Finally, I will show a remarkable correspondence between the evolution of the horizon geometry at late times and the quasi-normal modes which describe the ringdown signal measurable by far away observers.

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The talk's start time is 17:00 Jerusalem time, but we'll start gathering 30 minutes earlier for informal chat

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Abstract: In the presence of a black hole, light sources connect to observers along multiple paths. As a result, observed brightness fluctuations must be correlated across different times and positions in black hole images. Photons that execute multiple orbits around the black hole appear near a critical curve in the observer sky, giving rise to the photon ring. In the talk I will describe the structure of a Kerr black hole's photon ring. I will then discuss a novel observable we have recently proposed: the two-point correlation function of intensity fluctuations on the ring. This two-point function exhibits a universal, self-similar pattern consisting of multiple peaks of identical shape: while the profile of each peak encodes statistical properties of fluctuations in the source, the locations and heights of the peaks are determined purely by the black hole parameters. Measuring these peaks would demonstrate the existence of the photon ring without resolving its thickness, and would provide estimates of black hole mass and spin. With regular monitoring over sufficiently long timescales, this measurement could be possible via interferometric imaging with modest improvements to the Event Horizon Telescope.

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The talk's start time is 17:00 Jerusalem time, but we'll start gathering 30 minutes earlier for informal chat

- Marco Drago, Gran Sasso Science Institute, L'Aquila, Italy
Marco Drago, Gran Sasso Science Institute, L'Aquila, Italy
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A new astronomy started in 2015 with the first gravitational wave detection. Since then, LIGO-Virgo collaborations have confirmed several
events originating from the coalescence of binary systems composed by compact objects. While for these type of events the wave signature is
clear and well characterized, for other possible sources in the universe we are lacking of a complete modelization, so that it is necessary to
adopt alternative approaches to discover. We overview one of these approaches extensively used in the search for gravitational wave in the
LIGO-Virgo scientific runs, exploting its performances and possible applications. We also introduces the future challenges, when the next generation of detectors will become operative.

*Incidentally, Marco Drago was the first person to see a gravitational wave - and he'll be available to chat before and after the talk

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The talk's start time is 17:00 Jerusalem time, but we'll start gathering 30 minutes earlier for informal chat

- Almog Yalinewich, Canadian Institute for Theoretical Astrophysics, Toronto
Almog Yalinewich, Canadian Institute for Theoretical Astrophysics, Toronto
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Many astrophysical phenomena involve an abrupt release of a large amount of energy close to the surface of a large body. Examples include impacts on a terrestrial planet and outbursts from a neutron star while inside the common envelope of a giant star. In this talk I will present a new universal analytic solution that can describe the shock wave in all these scenarios. I will show that this shock wave satisfies a new kind of conservation law that lies somewhere in between energy and momentum conservation. This conservation law opens the door to a myriad of insights about a wide range of physical problems: the size and shapes of craters, atmospheric mass loss from giant impacts and oblique shock breakout from supernovae.

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The talk's start time is 17:00 Jerusalem time, but we'll start gathering 30 minutes earlier for virtual mingling and informal chat

- Tanmayee Gupte, Rochester Institue of Technology
Tanmayee Gupte, Rochester Institue of Technology
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The recent detection of gravitational waves (GW) from a system of binary neutron stars (BNS) in coincidence with electromagnetic observations has launched a new era of multimessenger astrophysics. As a result, BNS mergers are one of the main targets for GW interferometer detectors on earth. A particularly interesting challenge is to constraint the equation of state (EOS) of the nuclear matter inside the neutron star core, which is still theoretically unknown. In order to do parameter estimation and detect additional GW signals, we need to compare the observed signals to theoretical GW templates, which depend on different characteristics like total mass, EOS, mass ratio, etc. Limited work has been previously done with simulating unequal-mass BNS because of numerical difficulties. We have modified the LORENE code to advance our ability to construct unequal-mass BNS initial data, and used them to initiate dynamical evolutions of BNS mergers performed using the Einstein Toolkit. Here we discuss the importance of Initial Data and the modifications done to the LORENE code.

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The talk's start time is 17:00 Jerusalem time, but we'll start gathering 30 minutes earlier for informal chat

- Sivan Ginzburg, Berkeley
Sivan Ginzburg, Berkeley
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Black Widows are rapidly spinning magnetized neutron stars with companions that are only a few percent the mass of the Sun. I will present numerical stellar evolution tracks showing how main sequence stars are reduced to such low masses by magnetic braking and Roche-lobe overflow. The numerical results are explained by an analytical model, similar to the Hayashi track, but accounting for the pulsar’s gamma-ray irradiation. I will compare the theory to radio and gamma-ray observations of the pulsars, as well as to novel optical images of the companions themselves. I will demonstrate that the mass at which a Black Widow companion becomes fully convective is a simple function of its orbital period, allowing us to study stellar structure and magnetism away from the main sequence in a controlled manner.

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The talk's start time is 17:00 Jerusalem time, but we'll start gathering 30 minutes earlier for informal chat

- Ben Margalit, UC Berkeley
Ben Margalit, UC Berkeley
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The equation-of-state of cold asymmetric (neutron-rich) matter at supra-nuclear densities is a long-standing open question. It cannot currently be calculated from first principles theory (QCD), nor can this regime be directly probed through terrestrial experiments. Neutron stars (NSs) therefore provide a unique laboratory for studying cold dense matter. In this talk I will describe progress in this field obtained by utilizing both gravitational-wave and electromagnetic observations of NS mergers. An overview will be given of several different methods of constraining the equation-of-state using NS mergers, the strengths and caveats associated with each will briefly be discussed, as will the future outlook for this newly-emerging field.

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The talk's start time is 17:00 Jerusalem time, but we'll start gathering 30 minutes earlier for informal chat

- Vera Delfavero, Rochester Institute of Technology
Vera Delfavero, Rochester Institute of Technology
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Gravitational wave observations can now strongly differentiate between assumptions for how binary compact objects form. Different models for compact binary formation can be ranked by their similarity to GW observations, as a marginal likelihood. In this work, we show how to carefully interpolate this marginal likelihood between model parameters, enabling posterior distributions for these model parameters. Using the StarTrack binary evolution code, we compare one- and three-dimensional models to the compact binary mergers reported in GWTC-1. Consistent with prior work, with our one- dimensional models we infer that modest natal kicks are more consistent with the observed merger rates and mass distributions.

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The talk's start time is 17:00 Tel-Aviv time, but we'll start gathering 30 minutes earlier for informal chat

Note: Israel switches to Winter Time on October 25th, and the US on November 1st, so 17:00 in Tel-Aviv means 11:00 in Rochester

- Shmuel Bialy, Harvard Center for Astrophysics, Boston
Shmuel Bialy, Harvard Center for Astrophysics, Boston
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*** Recording available here: https://www.youtube.com/watch?v=qwhaQQBQY4c&feature=youtu.be ***

I will start with a broad review of the field of star formation and galaxy evolution, and some pressing open questions. I will then dive into the star-forming interstellar medium (ISM), asking the question, what regulates the star formation process?

I will discuss the multiphase structure of the ISM, key heating-cooling processes and chemical processes in the ISM, and interstellar turbulence, all of which may play an important role in regulating star formation. I will focus on a particularly appealing theory for star formation where gas heating by far-UV radiation from young stars (and by cosmic-rays in some galaxies), may provide a natural feedback loop, and thus organically self-regulate star-formation in galactic disks, and present recent results (Bialy 2020, ApJ accepted) for the link between star-formation rate and far-UV radiation intensity.

I will conclude with future prospects: Charting new ways for constraining poorly known interstellar properties: turbulence, 3D ISM structure, low energy cosmic-ray spectra, and our plan to construct an improved star-formation model for next-generation large scale cosmological simulations (i.e., IllustrisTNG successors).

The seminar will be hosted on Zoom: https://zoom.us/j/9290951953

The talk's start time is 17:00 Jerusalem time, but we'll start gathering 30 minutes earlier for virtual mingling and informal chat

- Nate Barlow, Rochester Institute of Technology (RIT), NY, USA
Nate Barlow, Rochester Institute of Technology (RIT), NY, USA
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An accurate closed-form solution is obtained to the SIR Epidemic Model and to the SEIR Epidemic Model through the use of Asymptotic Approximants (Barlow et al., 2017). An analytic solution is obtained to the SEIR Epidemic Model. The solution is created by constructing a single second-order nonlinear differential equation in ln(S) and analytically continuing its divergent power series solution such that it matches the correct long-time exponential damping of the epidemic model. The utility of the analytical form is demonstrated through its application to the COVID-19 pandemic.
Similar methods have been used to model geodesics around Kerr black holes, and are under development for modeling gravitational waveforms from binary black  hole mergers, from the inspiral to the ringdown stages.

The talk and discussion will be hosted on Zoom: https://zoom.us/j/9290951953
The start time is 8:30 EDT / 15:30 Jerusalem time.

- Srishti Tiwari, Tata Institute of Fundamental Research, Mumbai, India
Srishti Tiwari, Tata Institute of Fundamental Research, Mumbai, India
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PhD Thesis Synopsis for Srishti Tiwari, our incoming postdoc

Sivan Ginzburg, Berkeley
Sivan Ginzburg, Berkeley

Black widows are millisecond pulsars with low-mass companions (~2% the mass of the sun) on short orbits of several hours. When the first black widow was discovered in 1988, it was proposed that its companion is the remnant of a main sequence star that had been evaporated by the pulsar’s high energy radiation. I will present new observations from the last decade that challenge this picture, and discuss how the growing population of black widows can be explained consistently.

The talk will be given over Zoom, at: https://zoom.us/j/9290951953

The official talk starts at 16:30 Jerusalem Time (06:30 PDT), but we'll start preparing and mingling on Zoom from 16:00 and onwards

Marlin B. Schäfer, Albert Einstein Institute (AEI) Hannover, Germany
Marlin B. Schäfer, Albert Einstein Institute (AEI) Hannover, Germany

As two neutron stars merge, they emit gravitational waves that can potentially be detected by earth bound detectors. Matched-filtering based algorithms have traditionally been used to extract quiet signals embedded in noise. We introduce a novel neural-network based machine learning algorithm that uses time series strain data from gravitational-wave detectors to detect signals from non-spinning binary neutron star mergers. For the Advanced LIGO design sensitivity, our network has an average sensitive distance of 130 Mpc at a false-alarm rate of 10 per month. Compared to other state-of-the-art machine learning algorithms, we find an improvement by a factor of 6 in sensitivity to signals with signal-to-noise ratio below 25. However, this approach is not yet competitive with traditional matched-filtering based methods. A conservative estimate indicates that our algorithm introduces on average 10.2 s of latency between signal arrival and generating an alert. We give an exact description of our testing procedure, which can not only be applied to machine learning based algorithms but all other search algorithms as well. We thereby improve the ability to compare machine learning and classical searches.

The seminar will be given online via Zoom: https://zoom.us/j/9290951953

The official talk time is 16:30 Jerusalem Time (15:30 CEST), but we'll be around from 16:00 (15:00) for connection tests and chatter

Barak Shoshany, Perimeter Institute of Theoretical Physics
Barak Shoshany, Perimeter Institute of Theoretical Physics

I will discuss the possibility and feasibility of time travel within the context of general relativity and quantum field theory, the paradoxes resulting from it, and possible ways to resolve these paradoxes. The talk will be based on arXiv:1907.04178 and arXiv:1911.11590.

The talk will be given over Zoom, at: https://zoom.us/j/9290951953

The official talk starts at 16:30 Jerusalem Time (09:30 EDT), but we'll hstart mingling on Zoom from 16:00 and onwards

Paolo Marcoccia, University of Stavanger, Norway
Paolo Marcoccia, University of Stavanger, Norway

The first Gravitational Wave detection of GW150914 led to a revolution in the world of modern physics and astronomy,

beyond being an additional confirmation for the predictions of Einstein's General Relativity,

it opened the gates of Experimental Physics to data that couldn't have been observed in any other way before that,

and capable of testing theories that before the GW era had no other way of being proved.

In my talk, i'll analyze some of the LIGO results from a different point of view respect to the one commonly adopted by LIGO,

by looking for statistically significant correlations in the data between the LIGO gravitational wave detectors.

Said method, even though wouldn't be the best choice for a blind search of new gravitational wave events, may be used to infer  properties of already known detections,

as well as testing deviation of the data from the prediction of standard theories and test out new ones.

The seminar will be given over Zoom, at: https://zoom.us/j/9290951953

The time (16:30) is In Jerusalem Time (15:30 CEST)

- Na'ama Hallakoun, Weizmann Institute of Science
Na'ama Hallakoun, Weizmann Institute of Science
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The immediate surroundings of white dwarfs (WDs) are key to our understanding of a number of puzzles. Observations of WDs can reveal the presence of stellar, substellar, and stellar-remnant companions, planets, dust, atmospheric heavy elements, and planetary debris, each of relevance to several important questions. The remains of the pre-WD-phase solar systems are revealed in the form of heavy element 'pollution' in WD atmospheres, excess emission from dust discs, and–only recently–in transits of planetary debris. In principle, WDs can host not only debris, but also whole planetary systems. Binary systems consisting of two WDs are important in a broad range of astrophysical contexts, from stellar evolution, through Type-Ia supernova (SN Ia) progenitors, to sources of gravitational waves.

SNe Ia–supernova explosions of WDs–are a major source of heavy elements, and, as 'standard candles', they have provided one of the fundamental methods for estimating distances in the Universe. However, the nature of the progenitor systems of SNe Ia is still unclear. A progenitor scenario that has been long considered is the double-degenerate scenario, in which a double WD binary loses energy and angular momentum to gravitational waves, until merger and possible explosion as a SN Ia. If most SN Ia explosions are the result of double WD mergers, then the observed double WD merger rate should be high enough to account for the observed SN Ia rate.

In my talk I will present some of the clues we have found for these questions.

The talk will be given over Zoom, meeting link is  https://zoom.us/j/9290951953

Niayesh Afshordi
Niayesh Afshordi

I will start by motivating why some observational probes of astrophysical black holes in a quantum theory might be radically different from their classical ones. I will then show that these signatures can be best probed by searching for low frequency harmonics in the gravitational wave spectrum of perturbed black holes, what we call "quantum black hole seismology". Finally, I will end by summarizing the (controversial) observational status of these searches and their future outlook.

The seminar will be given over Zoom, at: https://zoom.us/j/9290951953

The time (16:30) is In Jerusalem Time (09:30 EDT)

The Event Horizon Telescope image of the supermassive black hole in the galaxy M87 is dominated by a bright, unresolved ring. General relativity predicts that embedded within this image lies a thin “photon ring,” which is composed of an infinite sequence of self-similar subrings that are indexed by the number of photon orbits around the black hole. The subrings approach the edge of the black hole “shadow,” becoming exponentially narrower but weaker with increasing orbit number, with seemingly negligible contributions from high order subrings. In the talk, I will discuss the structure of the photon ring, starting with non-rotating black holes, and then proceed to the complex patterns that emerge when rotation is taken into account. Subsequently I will argue that the subrings produce strong and universal signatures on long interferometric baselines. These signatures offer the possibility of precise measurements of black hole mass and spin, as well as tests of general relativity, using only a sparse interferometric array.

The talk will be given over Zoom, meeting link is  https://zoom.us/j/9290951953

- Yotam Sherf, Ben-Gurion University
Yotam Sherf, Ben-Gurion University
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We study the emission of gravitational waves, gravitons, photons and neutrinos from a perturbed Schwarzschild blackhole (BH).The perturbation can be due to either classical or quantum sources and therefore the injected energy can be either positive or negative.The emission can be classical in nature, as in the case of gravitational waves, or of quantum nature, for gravitons and the additional fields. We first setup the theoretical framework for calculating the emission by treating the case of a minimally coupled scalar field and then present the results for the other fields. We perform the calculations in the horizon-locking gauge in which the BH horizonis deformed, following similar calculations of tidal deformations of BH horizons.The classical emission can be interpreted as due to a partial exposure of a nonempty BH interior, while the quantum emission can be interpreted as an increased Hawking radiation flux due to the partial exposure of the BH interior. At the end we demonstrate that the quantum emission in BHs that are far away from equilibrium is comparable and even larger than the Hawking radiation

- Uri Malamud
Uri Malamud
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Exomoons orbiting terrestrial or super-terrestrial exoplanets have not yet been discovered; their possible existence and properties are therefore still an unresolved question. I will present results from a recent study about the collision-formation of massive exomoons, and discuss the plausibility of detecting them currently or in the future. We are also able to infer the existence of exo-solar moons, dwarf and minor planets from the observation of polluted white dwarf atmospheres, which probe their bulk composition. Small planetary objects with tidal crossing orbits disrupt around the white dwarf and form a disk of debris, which later accrete onto the white dwarf and pollute its atmosphere. Progress in the last decade, has shown this material to be typically dry, i.e., with terrestrial-like chemical composition and lacking in water. l will discuss results from a series of studies which examine whether water-bearing small planetary objects even have the potential to retain their water, as they undergo thermal, physical, chemical and orbital evolution during the high luminosity stellar evolution phases of their host stars. If time permits I will talk briefly about new hybrid approaches for modeling the aforementioned tidal disruptions and generating debris disks.

- Dr. Jonathan Stern
Dr. Jonathan Stern
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Gas in dark matter halos, known as the circumgalactic medium (CGM), is both the source of fuel for star formation in the galaxy and the destination of galaxy outflows. The CGM is thus expected to play a fundamental role in galaxy evolution. I will revisit the question of the virialization of the CGM, in which the volume-filling gas phase transitions from being predominantly cool and free-falling at low halo masses to predominantly hot and quasi-static at high halo masses. Using both an idealized model and the FIRE cosmological simulations, I will demonstrate that several aspects of this process have not been previously appreciated despite over four decades of research. I will then show that CGM virialization in FIRE is associated with an abrupt change in the properties of star formation and outflows in the central galaxy, and with the formation of a galaxy disc.
David Eichler
David Eichler

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נעמי גלובוס
נעמי גלובוס

Cosmic-rays are one of the most fascinating phenomena in the universe. They consist of energetic particles with an out-of-equilibrium power-law spectrum extending over at least eleven orders of magnitude in energy, from ~1 GeV to 10^11 GeV. In the past decade, new measurements by experiments such as the Pierre Auger observatory and Telescope Array, have greatly improved our knowledge of the highest energy domain of the cosmic-ray spectrum, the "ultra-high energy cosmic-rays" (UHECR), with energies > 10^9 GeV. At these energies, cosmic-rays are thought to be of extragalactic origin and they are highly challenging by questions with respect to their origins and their acceleration processes.

I will first review the observational data on the cosmic-ray spectrum, composition and arrival directions. I will show that the spectrum and composition can be explained by a generic model having one Galactic component and one extragalactic component. I will review the multi-messenger constrains brought by neutrino and gamma-ray experiments on UHECR origin. Finally, I will discuss the origin of the UHECR dipole anisotropy recently reported by the Pierre Auger Observatory.

אופק בירנהולץ
אופק בירנהולץ
Introducing the physics of gravitational waves and compact binary coalescences, and their detection and analysis by LIGO. Focusing on the catalog from LIGO's first 2 Observation runs O1+O2, as well as engagement opportunities for new students and researchers towards O3, and the future of LIGO and next generation detectors.
אלינור מידז׳ינסקי
אלינור מידז׳ינסקי

The most fundamental question in observational cosmology today is what is the nature of dark energy and dark matter. As the most massive gravitationally bound bodies in the Universe, clusters of galaxies serve as beacons to the growth of structure over cosmic scales, making them a sensitive cosmological tool. However, accurately measuring their masses has been notoriously difficult. Weak lensing provides the best direct probe of the cluster mass, both the baryonic and dark components, but it requires high-quality wide-field imaging. With its unprecedentedly deep and exquisite seeing, the Subaru Hyper Suprime-Cam (HSC) survey is an ongoing campaign to observe 1,400 square degrees. In this talk, I will present our new field-leading results from the first HSC data release of ~150 square degrees that encompass thousands of clusters. Harnessing our new HSC survey, I measure benchmark weak lensing cluster masses, and reconcile previous tension on cosmological parameters between the SZ and CMB within the Planck survey. The next generation of wide-field surveys is almost upon us, with the Large Synoptic Survey Telescope (LSST), WFIRST and several more coming online. They will discover hundreds of thousands of galaxy clusters, peering deep to the epoch of formation. I will describe these exciting new surveys and the multifold breakthrough science we will achieve in the new era of astronomy.

אביב אופיר
אביב אופיר

Exoplanets are almost never visible and thus remained unknown over centuries of astronomical research.  In this talk, I will explain how exciting discoveries of new worlds are now made, and surprising aspects of their characteristics are determined. This is accomplished by creative methods and dedicated telescopes on Earth and in space.  I will review the observational techniques for studying exoplanets and focus on transits – the passage of an exoplanet in front of its host star.  This seemingly simple geometry allows a surprising array of insights: from detailed transit analysis, we constrain the most fundamental planetary properties relevant for the system architecture, theories of planet formation, evolution, composition, global weather patterns, and some day, even biomarkers.  The relentless pace of discovery during the past two decades is expected not only to continue but even intensify in the future.

יוסי שוורצולד
יוסי שוורצולד

Over the last three decades, our knowledge about planetary systems has increased dramatically, from one example with eight planets (our own Solar system) to over 2800 planetary systems hosting more than 3700 planets. While occurrence rate studies show that exoplanets are the rule rather than an exception, our understanding of the physical processes forming these planets is still very limited. Fortunately, we are now on the verge of the next revolution in exoplanet science. TESS, PLATO, JWST, WFIRST, and LSST will complete the demographic census of planets across a wide range of environments, and will allow detailed characterization of their atmospheres and structure.

In this talk I will discuss the important role of microlensing in the forefront of exoplanetary studies. Gravitational microlensing is unique in its ability to probe several important but relatively untapped reservoirs of exoplanet parameter space, including the abundance and mass-function of cold planets, planet-formation efficiency in different Galactic environments, and the population of free-floating planets. A wealth of new and upcoming microlensing campaigns, both from ground and space, will allow the full exploration of the exoplanet demographics unique to microlensing, potentially revolutionizing our understanding of planet formation. In addition to studying planets, these surveys allow to study important regimes of the stellar mass function (e.g., massive remnants, isolated brown-dwarfs) and to to study the Galactic structure and evolution.