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SUMMARY:Very Massive\, Rapidly Spinning Binary Black Hole Progenitors thro
 ugh Chemically Homogeneous Evolution—The Case of GW231123
DTSTART:20260427T123000Z
DTEND:20260427T124500Z
DTSTAMP:20260509T080000Z
UID:indico-event-1804@indico.dfa.unipd.it
DESCRIPTION:Speakers: Martina Mattiussi (Università degli Studi di Padova
 )\n\n\nAmong the over 200 gravitational wave detections reported so far\, 
 GW231123 is a remarkable event that not only holds the record for the most
  massive black hole merger but also exhibits extreme spins. Its origin is 
 actively debated. Proposed scenarios include dynamical formation through h
 ierarchical mergers\, Population III stars\, accretion in active galactic 
 nucleus disks and also more exotic explanations including primordial black
  holes and cosmic strings\, each facing different challenges. Recent work 
 showed that the incoming black holes of GW231123 could form from massive\,
  rapidly rotating collapsing helium stars. Here\, we address the question 
 how such stars can be formed in very close binary systems and explore chem
 ically homogeneous evolution (CHE) involving progenitors with masses above
  the pair-instability mass gap. We compute a grid of detailed massive bina
 ry models with the stellar evolution code MESA to follow the early evoluti
 on of binary progenitors and show that (i) very massive (Mi > 140 M⊙) C
 HE binaries at low metallicity (Z = 10−5) naturally produce rapidly rota
 ting progenitors with high masses and high spins matching the properties o
 f the black holes in GW231123 and (ii) the maximum spin of the progenitors
  is bound by their critical rotation rate\, producing a tight correlation 
 between the dimensionless spin and mass\, a ∝ M−0.9\, in models withou
 t any hydrogen left. We conclude that the CHE channel appears to be a viab
 le and natural scenario to produce progenitors. We compare and discuss the
  differences with earlier studies and comment on the large uncertainties i
 n the final fate and collapse.\n\n\n\nhttps://indico.dfa.unipd.it/event/18
 04/
LOCATION:Aula Rosino (Dipartimento di Fisica e Astronomia - Edificio ex-Ri
 zzato)
URL:https://indico.dfa.unipd.it/event/1804/
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