[ExI] Visible light from two Black Holes with the help of a third

[John Clark]

For the first time astronomers think they may have detected the
Gravitational Waves from the merger of two black holes and also visible
light emissions from the collision; light from neutron star smash ups have
been seen before but not from black holes. On May 21 2019 LIGO detected a
merger 4 billion light years away of 2 black holes of about equal size that
resulted in a new hole of at least 100 solar masses. At first astronomers
detected no flash but 34 days later a quasar in the right place in the sky
that was 4 billion light years away underwent a very unusual visible flare
and there is reason to think the two things may be related. Gravitational
waves carry an enormous amount of energy but for them to heat up gas to
incandescence it would have to be extremely close to the source of those
waves and be very dense, there is only one place that fits that bill, the
accretion disk around an even larger black hole.

A model was developed in which the two black holes were in orbit in the
accretion disk around a third black hole, a supermassive one of about 100
million solar masses. In such a situation the Gravitational Waves would
heat the gas to enormous temperatures but it would take about a month for
that spike of heat energy to work its way to the outside of the accretion
disk so it could be radiated away and let us see it. They made a testable
prediction to figure out if the model is correct. The black holes were
spinning very rapidly so If the model is right the new merged hole would
shoot up at right angles to the accretion disk at about 120 miles a second
which would shut off the flare, but the black hole would then fall back
down through the disk again in 1.6 years, so they predict we should see the
quasar give out another unusual flair around Christmas time of this year.

Candidate Electromagnetic Counterpart to the Binary Black Hole Merger
Gravitational-Wave Event S190521g
<https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.251102>

John K Clark
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