Kavli Affiliate: Pau Amaro Seoane
| First 5 Authors: Taeho Ryu, Pau Amaro Seoane, Andrew M. Taylor, Sebastian T. Ohlmann,
| Summary:
In stellar-dense environments, stars can collide with each other. For
collisions close to a supermassive black hole (SMBH), the collisional kinetic
energy can be so large that the colliding stars can be completely destroyed,
potentially releasing an amount of energy comparable to that of a supernova.
Such violent collisions, which we call BH-driven disruptive collisions (BDCs),
have been examined mostly analytically, with the non-linear hydrodynamical
effects being left largely unstudied. Using the moving-mesh hydrodynamics code
{small AREPO}, we investigate high-velocity ($>10^{3}$ km/s) collisions
between 1M$_{odot}$ giants with varying radii, impact parameters, and initial
approaching velocities, and estimate their observables. Very strong shocks
across the collision surface efficiently convert $gtrsim10%$ of the initial
kinetic energy into radiation energy. The outcome is a gas cloud expanding
supersonically, homologously, and quasi-spherically, generating a flare with a
peak luminosity $simeq 10^{41}-10^{44}$ erg/s in the extreme UV band ($simeq
10$ eV). The luminosity decreases approximately following a power-law
$t^{-0.7}$ initially, then $t^{-0.4}$ after $tsimeq$10 days at which point it
would be bright in the optical band ($lesssim 1$eV). Subsequent, and possibly
even brighter, emission would be generated due to the accretion of the gas
cloud onto the nearby SMBH, possibly lasting up to multi-year timescales. This
inevitable BH-collision product interaction can contribute to the growth of BHs
at all mass scales, in particular, seed BHs at high redshifts. Furthermore, the
proximity of the events to the central BH makes them a potential tool for
probing the existence of dormant BHs, even very massive ones which cannot be
probed by tidal disruption events.
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