Blackhole Mergers Were Suspected Of Producing Flashes Of Light
As a result of the collision of black holes, not only gravitational waves can occur, but also flashes of light. To do this, such a merger must occur near a supermassive black hole. This conclusion was reached by astronomers, whose article was published in the scientific journal Physical Review Letters.
"The supermassive black hole at the center of the galaxy J1249+3449, where The gw190521g flash occurred, was peacefully "snuffling" for a long time before this burst occurred. It was formed at the same time and in the same place where the gravitational waves came from. We believe that the source of this flash was the merging of black holes, but we can not rule out other scenarios," said one of the authors of the article, scientific Director of the ZTF Observatory Matthew Graham.
Scientists believe that mergers of pairs of black holes, as well as single black holes and other compact objects, can not be sources of flashes of light or other types of electromagnetic radiation. In fact, such events can only be detected using gravitational wave detectors such as LIGO and VIRGO. These tools track how space-time is "stretched" by gravitational waves.
The fact that this statement may be incorrect, scientists learned in 2016. At that time, astronomers working with the Fermi telescope said that they had detected a faint flash of light, the source of which was the event GW150914, which was the first experimental confirmation that gravitational waves exist. However, later astronomers doubted their discovery. Now scientists have only been able to record flashes of light from the mergers of pairs of neutron stars – the so-called "kilon," but not black holes and other objects.
Graham and his colleagues believe that they have discovered the first example of a light flash, the source of which was the merger of two black holes. They came to this conclusion by studying data from the ZTF telescope, which is designed to search for supernovae and other similar events.
Light and gravity
Analyzing images of the part of the constellation of Veronica Hair where the gw190521g flash was recorded, the participants of the ZTF project noticed that the supermassive black hole in the center of the galaxy J1249+3449 in this area of space unexpectedly "woke up" and produced a powerful flash of light.
Initially, scientists assumed that this burst of supermassive black hole activity simply coincided with the birth of GW190521g. Subsequent analysis of the timing of this flash, its strength, and other parameters indicated that this coincidence was not an accident. As astrophysicists suggest, both gravitational waves and a flash of light were generated by the collision of two stellar-mass black holes, which are located next to a heavier black hole.
This visible flash of light, scientists believe, was caused by the fact that a pair of black holes were inside the accretion disk – a "bagel" of incandescent matter and gas that surrounds the supermassive black hole. As a result of their merger, a new, larger black hole was "catapulted" from this disk. Because of this, the surrounding matter warmed up and formed a flash.
In favor of this, in particular, says that the duration of this flash, its spectrum, and some other characteristics are not similar to standard light sources in the vicinity of supermassive black holes. This usually happens when the attraction of a black hole tears a star apart, or when the star ends its life in a supernova explosion.
In addition, during the previous 15 years of observations, until May 2019, the level of activity of this supermassive black hole was quite low. This calls into question the fact that it suddenly "awoke" and began to absorb large amounts of matter from the surrounding disk of gas and dust.
Final confirmation of this theory, as expected by Graham and his colleagues, can be obtained in a few years, when the newborn black hole once again flies through the accretion disk and generates a new flash. At the same time, scientists hope that they will be able to track other similar events in the near future when LIGO and VIRGO will start working again.