Black Hole Collision May Have Exploded With Light
In a first, astronomers may have seen light from the merger of two black holes, providing opportunities to learn about these mysterious dark objects.
When two black
holes spiral around each other and ultimately collide, they send out gravitational
waves - ripples in space and time that can be detected with extremely sensitive
instruments on Earth. Since black holes and black hole mergers are completely
dark, these events are invisible to telescopes and other light-detecting
instruments used by astronomers. However, theorists have come up with ideas
about how a black hole merger could produce a light signal by causing nearby
material to radiate.
Now, scientists
using Caltech's Zwicky Transient Facility (ZTF) located at Palomar Observatory
near San Diego may have spotted what could be just such a scenario. If
confirmed, it would be the first known light flare from a pair of colliding black
holes.
The merger was
identified on May 21, 2019, by two gravitational wave detectors - the National
Science Foundation's Laser Interferometer Gravitational-wave Observatory (LIGO)
and the European Virgo detector - in an event called GW190521g. That detection
allowed the ZTF scientists to look for light signals from the location where
the gravitational wave signal originated. These gravitational wave detectors
have also spotted mergers between dense cosmic objects called neutron stars,
and astronomers have identified light emissions from those collisions.
The ZTF results
are described in a new study published in the journal Physical Review Letters.
The authors hypothesize that the two partner black holes, each several dozen
times more massive than the Sun, were orbiting a third, supermassive black hole
that is millions of times the mass of the Sun and surrounded by a disk of gas
and other material. When the two smaller black holes merged, they formed a new,
larger black hole that would have experienced a kick and shot off in a random
direction. According to the new study, it may have plowed through the disk of
gas, causing it to light up.
"This
detection is extremely exciting," said Daniel Stern, coauthor of the new
study and an astrophysicist at NASA's Jet Propulsion Laboratory in Southern
California, which is a division of Caltech. "There's a lot we can learn
about these two merging black holes and the environment they were in based on
this signal that they sort of inadvertently created. So the detection by ZTF,
coupled with what we can learn from the gravitational waves, opens up a new
avenue to study both black hole mergers and these disks around supermassive
black holes."
The authors note
that while they conclude the flare detected by ZTF is likely the result of a
black hole merger, they cannot completely rule out other possibilities.
To learn more, read
the press release from Caltech.
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