AstroPhysics Seminar

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Previous Lectures

נעמי גלובוס
30/12/2018 - 10:30

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
23/12/2018 - 10:30
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
16/12/2018 - 10:30

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
18/11/2018 - 10:30

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
11/11/2018 - 10:30

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.