Fragmentation in Collapsar Disks: Migration, Growth, and Emission

QUEST Center event
No
Speaker
Yonatan Lerner, Hebrew University of Jerusalem, Israel
Date
28/05/2025 - 15:00 - 13:30Add to Calendar 2025-05-28 13:30:00 2025-05-28 15:00:00 Fragmentation in Collapsar Disks: Migration, Growth, and Emission We present a parameter survey of fragmentation in collapsar disks,using a revised version of the Chen and Beloborodov (2007) model thatdetermines the structure of steady state hyperaccretion disks in a generalrelativistic and neutrino cooled framework. We map out the range of diskconditions leading to gravitational instability alongside an exploration ofthe dimensionless cooling time β, which together determine whether fragmentationis likely to occur. We estimate the initial mass and densityof fragments, finding that they occupy a unique region in the space ofself-gravitating compact objects, with masses Mf ∼ 10−3M⊙ − 10−1M⊙and densities ρf ∼ 108 − 1011 g cm−3. We then calculate their migrationand mass growth (via Bondi-Hoyle accretion) as they inspiral through thecollapsar disk. During a fragment’s migration to the central black hole,it can grow its mass up to a range Mf ∼ 10−1M⊙ − 1M⊙. In most cases,the final fragment mass is larger than the minimum cold stable neutronstar mass but much smaller than any observed neutron star. The fragmentbriefly achieves peak accretion rates comparable to (or even largerthan) that of the central engine. We propose that these bound fragmentsmay give rise to observable astrophysical phenomena, and we approximatelymodel two of these: (i) gamma ray burst variability producedby a secondary, fragment-launched jet; (ii) the generation of non-vacuumgravitational waveforms accompanied by electromagnetic counterparts. Physics Building 202 Seminar Room 303 המחלקה לפיזיקה physics.dept@mail.biu.ac.il Asia/Jerusalem public
Place
Physics Building 202 Seminar Room 303
Abstract

We present a parameter survey of fragmentation in collapsar disks,
using a revised version of the Chen and Beloborodov (2007) model that
determines the structure of steady state hyperaccretion disks in a general
relativistic and neutrino cooled framework. We map out the range of disk
conditions leading to gravitational instability alongside an exploration of
the dimensionless cooling time β, which together determine whether fragmentation
is likely to occur. We estimate the initial mass and density
of fragments, finding that they occupy a unique region in the space of
self-gravitating compact objects, with masses Mf ∼ 10−3M⊙ − 10−1M⊙
and densities ρf ∼ 108 − 1011 g cm−3. We then calculate their migration
and mass growth (via Bondi-Hoyle accretion) as they inspiral through the
collapsar disk. During a fragment’s migration to the central black hole,
it can grow its mass up to a range Mf ∼ 10−1M⊙ − 1M⊙. In most cases,
the final fragment mass is larger than the minimum cold stable neutron
star mass but much smaller than any observed neutron star. The fragment
briefly achieves peak accretion rates comparable to (or even larger
than) that of the central engine. We propose that these bound fragments
may give rise to observable astrophysical phenomena, and we approximately
model two of these: (i) gamma ray burst variability produced
by a secondary, fragment-launched jet; (ii) the generation of non-vacuum
gravitational waveforms accompanied by electromagnetic counterparts.

תאריך עדכון אחרון : 19/05/2025