Starfall: A heavy rain of stars in ‘turning on’ AGN. (arXiv:2110.03741v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+McKernan_B/0/1/0/all/0/1">B.McKernan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ford_K/0/1/0/all/0/1">K.E.S. Ford</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cantiello_M/0/1/0/all/0/1">M. Cantiello</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Graham_M/0/1/0/all/0/1">M.J. Graham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jermyn_A/0/1/0/all/0/1">A.S. Jermyn</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Leigh_N/0/1/0/all/0/1">N.W.C. Leigh</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ryu_T/0/1/0/all/0/1">T. Ryu</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stern_D/0/1/0/all/0/1">D. Stern</a>
As active galactic nuclei (AGN) `turn on’, some stars end up embedded in
accretion disks around supermassive black holes (SMBHs) on retrograde orbits.
Such stars experience strong headwinds, aerodynamic drag, ablation and orbital
evolution on short timescales. Loss of orbital angular momentum in the first
$sim 0.1$~Myr of an AGN leads to a heavy rain of stars (`starfall’) into the
inner disk and onto the SMBH. A large AGN loss cone ($theta_{rm AGN,lc}$) can
result from binary scatterings in the inner disk and yield tidal disruption
events (TDEs). Signatures of starfall include optical/UV flares that rise in
luminosity over time, particularly in the inner disk. If the SMBH mass is
$M_{rm SMBH} ge 10^{8}M_{odot}$, flares truncate abruptly and the star is
swallowed. If $M_{rm SMBH}<10^{8}M_{odot}$, and if the infalling orbit lies
within $theta_{rm AGN,lc}$, the flare is followed by a TDE which can be
prograde or retrograde relative to the AGN inner disk. Retrograde AGN TDEs are
over-luminous and short-lived as in-plane ejecta collide with the inner disk
and a lower AGN state follows. Prograde AGN TDEs add angular momentum to inner
disk gas and so start off looking like regular TDEs but are followed by an AGN
high state. Searches for such flare signatures test models of AGN `turn on’,
SMBH mass, as well as disk properties and the embedded population.
As active galactic nuclei (AGN) `turn on’, some stars end up embedded in
accretion disks around supermassive black holes (SMBHs) on retrograde orbits.
Such stars experience strong headwinds, aerodynamic drag, ablation and orbital
evolution on short timescales. Loss of orbital angular momentum in the first
$sim 0.1$~Myr of an AGN leads to a heavy rain of stars (`starfall’) into the
inner disk and onto the SMBH. A large AGN loss cone ($theta_{rm AGN,lc}$) can
result from binary scatterings in the inner disk and yield tidal disruption
events (TDEs). Signatures of starfall include optical/UV flares that rise in
luminosity over time, particularly in the inner disk. If the SMBH mass is
$M_{rm SMBH} ge 10^{8}M_{odot}$, flares truncate abruptly and the star is
swallowed. If $M_{rm SMBH}<10^{8}M_{odot}$, and if the infalling orbit lies
within $theta_{rm AGN,lc}$, the flare is followed by a TDE which can be
prograde or retrograde relative to the AGN inner disk. Retrograde AGN TDEs are
over-luminous and short-lived as in-plane ejecta collide with the inner disk
and a lower AGN state follows. Prograde AGN TDEs add angular momentum to inner
disk gas and so start off looking like regular TDEs but are followed by an AGN
high state. Searches for such flare signatures test models of AGN `turn on’,
SMBH mass, as well as disk properties and the embedded population.
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