This artist’s concept shows a supermassive black hole surrounded by a disk of gas. Embedded in this disk are two smaller black holes that may have merged together to form a new black hole. Image credit: Caltech/R. Hurt (IPAC)
Jet Propulsion Laboratory (Pasadena CA)
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 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 (event horizon), causing it to light up.
Mergers of black holes are not well understood except that the angular momentum of each black hole is likely different. The merger of the material in (if we can use that term) and around each black hole will be moving at different directions and different speeds and it causes the new, larger black hole to travel in a new direction because of the energy released. That’s the theory.
It’s important to understand events such as these with neutron stars in particular.
Below is an updated periodic table of elements that shows where each element comes from. Some come from more than one source, but you can see just how many elements were detected in the neutron star merger. The purple shows elements from neutron star mergers. This is why the detected merger was so important. It showed us where many of the heavy elements came from like gold, silver, lead, platinum, iodine, bismuth, tin, uranium, and many more.