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Thanks to gravitational wave astronomy, we better understand what happens during the collision of black holes. But black holes in close orbit generate in space-time only ripples strong enough to be detected just before they burst. What happens before then? We can only extrapolate.
But a new discovery could change all that. In a galaxy located just over 2.5 billion light years from Earth, astronomers have spotted two supermassive black holes intended for a colossal crash.
Do not be too excited. They are still far apart, and astronomers estimate that it may be another 2.5 billion years to meet them. But we can still learn a lot from them, even though we will not be there to see the fireworks.
The greater promise of this discovery allows us to better understand the background of gravitational waves, a hypothetical buzz of low frequency gravitational waves from sources such as supermassive black holes about to merge.
We have not yet detected this noise – it is outside the scope of our current instruments. But now that we have a pair of supermassive black holes in their field of view, their characteristics provide astronomers with an estimate of the number of pairs of this type that could exist, potentially producing this gravitational background noise.
"It sounds a little like a chaotic song of crickets singing in the night," said astrophysicist Andy Goulding of Princeton University. "You can not discern one cricket from another, but the volume of the noise helps you to estimate the number of locusts that exist."
Having a good understanding of this noise could help us determine if the supermassive black holes are getting confused.
Until now, our detections of black hole collisions have been much less spectacular than stellar black holes; The most powerful gravitational wave detection to date was a collision between black holes 50 and 34 times larger than the mass of the Sun.
Supermassive black holes are another category. Each of these newly discovered pairs is estimated at 400 million times the mass of the Sun; and each is the core of a galaxy, the two joining in a galactic collision.
What will the core of this final galaxy look like? Will it act from a giant supermassive black hole representing 800 billion times the mass of the Sun or, as they get closer, will the two black holes get stuck in a perpetual orbit?
"It's a big disadvantage for astronomy not to know if supermassive black holes are coming together," said astrophysicist Jenny Greene of Princeton University. "For all black hole physics specialists, it's a long-standing puzzle that we need to solve."
According to the theoretical modeling, when two galaxies merge, their black holes are inexorably close together, transferring their orbital energy to the gas and the stars that surround them and thus gravitate in a spiral of ever narrower.
We know that pairs of star-mass black holes will eventually merge and form a single object, but with supermassive black holes, there is a problem.
As their orbit narrows, the region of space to which they can transfer energy also decreases. By the time they are separated from a parsec (about 3.2 light years), theoretically, this region of space is no longer large enough to withstand further degradation of the I / O. orbit. They therefore remain in a stable binary orbit, potentially for billions of years. This is what is called the last problem of parsec.
If we could see a binary galactic core, we could solve that problem, but at a distance of one parsec, colliding black holes would be too close to each other to distinguish them (although a candidate has been spotted) … well, you know how difficult it is to see a black hole at all.
This newly discovered couple is still found at around 430 parsecs (1,400 light-years), so they will not directly solve the final parsec problem – but they are still useful as they gave the researchers a better estimate from the time elapsed the collision would start to produce detectable gravitational waves.
We are not there yet. But by analyzing this newly discovered pair of black holes in the context of a hypothetical gravitational wave background, the team was able to arrive at an estimate of about 112 super-massive black holes confused at a detection distance from the Earth .
It's a pretty good amount close to us so we can have the first gravitational wavelength detection in a few years.
If the gravitational background is full of noise coming from pairs of supermassive black holes, in one way or another, they actually manage to close the last parsec between them.
And, if we do not detect this noise, maybe the parsec is really insurmountable.
The search was published in The letters of the astrophysical journal.
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