Two black holes accidentally met and created something never seen before: ScienceAlert
A ripple in space-time created by the collision black holes they taught us a lot about these enigmatic objects.
These gravitational waves they encode information about black holes: their masses, the shape of their inner spirals relative to each other, their spins, and their orientations.
From this, scientists determined that most collisions we saw were between black holes in binary systems. The two black holes began as a binary cluster of massive stars that turned into black holes together, then spiraled in and merged.
Of the 90 or so mergers discovered so far, however, one stands out as very unusual. Discovered in May 2019, GW19052 emitted space-time waves like no other.
“Its morphology and explosion-like structure are very different from previous observations,” says astrophysicist Rosela Gamba University of Jena in Germany.
She adds“GW190521 was originally analyzed as a merger of two rapidly rotating supermassive black holes approaching each other along nearly circular orbits, but its special characteristics led us to propose other possible interpretations.”
Specifically, the short, sharp duration of the gravitational wave the signal was difficult to explain.
Gravitational waves are generated the actual merger of two black holes, like waves from a stone dropped into a pond. But they are also generated by the binary inspiral, and the intense gravitational interaction sends out weaker waves as the two black holes inexorably move closer together.
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“The shape and brevity – less than a tenth of a second – of the signal associated with the event lead us to hypothesize an instantaneous merger of two black holes, which occurred in the absence of a spiral phase. explains astronomer Alessandro Nagar National Institutes of Nuclear Physics in Italy.
There is more than one way to end up with a pair of black holes in gravitational interaction.
The first is that the two have been together for a long time, perhaps even since the formation of baby stars from the same piece of molecular cloud in space.
The second is when two objects moving through space pass close enough to become gravitationally locked in what is known as a dynamical encounter.
That’s what Gamba and her colleagues thought might be happening with GW190521, so they designed simulations to test their hypothesis. They smashed pairs of black holes, tweaking parameters such as trajectory, spin and mass, to try to reproduce the strange gravitational wave signal detected in 2019.
Their results suggest that the two black holes didn’t start out in a binary system, but were instead caught in each other’s gravitational net, blasting past each other twice on a wild, eccentric loop before crashing into a larger one. a black hole. And none of the black holes in this scenario were spinning.
“By developing precise models using a combination of state-of-the-art analytical methods and numerical simulations, we found that highly eccentric coupling in this case explains the observation better than any other hypothesis previously put forward,” says astronomer Matteo Breschi University of Jena.
“The probability of error is 1 in 4,300!”
This scenario, the team says, is more likely in a densely populated region of space, such as a star cluster, where such gravitational interactions are more likely.
This tracks with previous findings about GW190521. One of the black holes in the merger was measured about 85 times mass of the Sun.
According to our current models, black holes larger than 65 solar masses cannot form from a single star; the only way we know a a black hole of that mass can be created by a merger between two objects of smaller mass.
The work by Gamba and her colleagues found that the masses of the two colliding black holes are about 81 and 52 solar masses; that’s slightly lower than previous estimates, but one of the black holes is still out of the way of forming a single star’s core collapse.
It is still unclear whether our models need tuning, but hierarchical mergers – where larger structures are formed through the continuous merging of smaller objects – are more likely in a cluster environment with a large population of dense buildings.
Dynamical encounters between black holes are considered to be quite rare, and gravitational wave The data collected by LIGO and Virgo to date seem to support this. However, rare does not mean impossible, and the new paper suggests that GW190521 may be the first we’ve discovered.
And the first means that there could be more of them in the years ahead. The gravitational wave observatories are currently being upgraded and maintained, but will be back online March 2023 for a new observation. This time, LIGO’s two detectors in the US and the Virgo detector in Italy will join KAGRA in Japan for even greater observational power.
More detections like GW190521 would be amazing.
The research was published in Natural astronomy.
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