Dancing black holes

Using the supersharp radio “vision” of the National Science Foundation’s VLBA, astronomers have made the first detection of orbital motion in a pair of supermassive black holes in a galaxy some 750 million light-years from Earth.

The two black holes, with a combined mass 15 billion times that of the Sun, are likely separated by only about 24 light years, extremely close for such a system.

The galaxy the black holes are in, called 0402+379 after its location in the sky, was first observed in 1995. However, it is only with new observations that researchers have been able to see the two black holes independently.

For many years, proving the existence of binary black holes was made difficult because of the nature of black holes themselves, and the limited means of detection available. However, in the event that a pair of black holes were to merge, an immense amount of energy should be given off as gravitational waves, with distinctive waveforms that can be calculated using general relativity "This is the first pair of black holes to be seen as separate objects that are moving with respect to each other"
Why does this galaxy have two supermassive black holes?
The presence of two such objects simply indicates that the galaxy has undergone a merger in the relatively recent cosmic past. When two galaxies combine, each contributes a supermassive black hole to the final product and in time, these two supermassive black holes should also combine.
A combination of the two black holes in 0402+379 would create a burst of gravitational radiation, like the famous bursts recently discovered by the Laser Interferometer Gravitational Wave Observatory, but scaled up by a factor of a billion.

This theorized convergence between the black holes of 0402+379, however, may never occur. Given how slowly the pair is orbiting, we think the black holes are too far apart to come together within the estimated remaining age of the universe, unless there is an added source of friction.


Phedias Hadjicharalambous
Cyprus Astronomy Organisation
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