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SUMMARY:Supermassive black hole binaries and their spin evolution in gas-r
 ich circumbinary discs - Martin Bourne (IoA)
DTSTART:20240131T134000Z
DTEND:20240131T140500Z
UID:TALK211534@talks.cam.ac.uk
CONTACT:Hannah Uebler
DESCRIPTION:Supermassive black holes (SMBHs)\, which reside in the centres
  of massive galaxies\, grow over cosmic time either via accretion of mater
 ial or through mergers. For the latter\, the SMBHs must be brought close e
 nough together for gravitational wave (GW) emission to take effect and lea
 d to their coalescence. When galaxies merge\, their central SMBHs sink to 
 the centre of the new halos as dynamical friction shrinks their orbits\, w
 here they can eventually form binary SMBHs. Such binaries can be surrounde
 d by gaseous circumbinary discs (CBDs) that impact the binary evolution\, 
 potentially providing a channel to shrink the binary orbit via dynamical i
 nteractions and accretion\, and allow GWs to kick in. I will present 3D hy
 drodynamic simulations using the moving-mesh code Arepo that model gas-ric
 h CBDs around binary SMBH systems covering a range of binary parameters in
 cluding mass ratio\, eccentricity and inclination. Not only do the simulat
 ions able to accurately capture the CBD\, but thanks to novel refinement t
 echniques gas streams that penetrate the disc cavity and minidiscs that fo
 rm around the individual SMBHs are resolved. These streams and cavities pl
 ay an important role in torquing the binary and hence in shrinking its orb
 it. The evolution of the SMBH spin is also an important quantity to track 
 for many reasons including its impact on the direction and power of radio 
 jets\, as well as for predicting the recoil velocities of newly merged BHs
 \, which can leave an imprint on the resulting GW signal and impact the ev
 ent rate in future LISA observations. As such\, the simulations employ a s
 ub-grid Shakura-Sunyaev accretion disc model that allows us to track not o
 nly the SMBH mass evolution but also the spin evolution that arises due to
  the accretion of material from the CBD. Therefore\, we can track key time
 scales including binary inspiral times and spin alignment timescales. 
LOCATION:The Hoyle Lecture Theatre + Zoom 
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