An Unusual Gravitational Signal From A Strange Pair Of Black Holes Has Been Discovered
For the first time, astrophysicists were able to record gravitational waves from the merger of a double black hole with unequal masses. The monitoring Protocol is published on the LIGO project website.
The LIGO and Virgo collaborations look for cosmic gravitational waves that occur when black holes collide. Just over a year ago, on April 12, 2019, scientists from these collaborations discovered gravitational waves propagating in space-time from the collision of two black holes located 2.4 billion light-years from Earth.
Currently, the registration of gravitational waves is no longer unusual. But in this case, their source was an event that astronomers had never seen.
If earlier waves always came from two approximately equal in mass black holes, 20-40 times the mass of the Sun, the signal GW 190412 was received from a non-equilibrium binary system of black holes, one of which was 29.7 solar masses, and the other was three times less, only 8.4. By the way, this is the smallest of the black holes discovered so far.
"None of these masses is in itself too surprising. We know that black holes can be of this size. What is new is the mass ratio," explains one of the authors of the discovery, astronomer Christopher Berry from Northwestern University in the United States. This observation allows us to test our predictions for gravitational wave signals and is another piece of the puzzle about how double black holes form."
It's curious that the merging of such a system with two distinctly different-sized black holes produced a longer gravitational signal than any other merging of black holes. This was due to the fact that the GW 190412 event produced two different frequencies of waves propagating simultaneously, which is not observed when merging black holes with approximately the same mass.
The presence of different frequency waves allowed the authors to make another test of the General theory of relativity. They divided the gravitational wave signal into earlier and later parts and used equations to calculate the second part of each half's signal. The calculations completely coincided with the observations, which is one of the most significant confirmations of Einstein's General theory of relativity to date.
The large difference in the masses of black holes in a binary system has enabled scientists to more accurately measure some of the system's astrophysical properties.
"This large difference in mass means that we can more accurately measure several properties of the system: its distance from us, the angle at which we look at it, and the speed of rotation of a heavy black hole around its axis," according to a press release From the max Planck Society's Institute for gravitational physics in Hanover, Germany, according to an employee of the Institute who took part in the study, Roberto Cotesta.
The high speed of rotation of a heavy hole, according to scientists, serves as some hint to the question of the formation of such an unusual system. Astrophysical models suggest that the formation of binary black holes occurs when each of the stars of a binary star system collapses into a black hole, so they cannot create binary black holes with large mass discrepancies.
The rapid rotation of the larger black hole suggests that it may have merged with other black holes earlier, before the GW 190412 event. It is possible that scientists are now observing a remnant from this triple or quadruple star system.