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by black holes, a collision doesn’t have to be a once-in-a-lifetime experience, new research suggests.
On April 12, 2019, scientists detected a new black hole merger using a trio of gravitational wave detectors. Astrophysicists have detected these events before, but something in the signals was different this time: the two black holes that collided were incredibly uneven, the largest being approximately three times the size of the smallest. Scientists did not expect to see such an unbalanced merger between black holes, and now they believe they could understand the unusual event.
“This event is a weirdo that the universe has thrown at us, it was something we did not see coming,” Salvatore Vitale, a physicist at the Massachusetts Institute of Technology and author of the new research, said in a statement. “But nothing happens once in the universe. And something like this, although rare, we will see again and we can say more about the universe.”
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Vitale and his colleagues suspect that the strange collision occurred after the largest black hole was the product of a merger of black holes. The initial event sent a large black hole bouncing around a neighborhood. full of black holessays this hypothesis, allowing uneven collision.
That’s a very different story than scientists’ two main scenarios for black hole mergers, which encourage fairly uniform coincidences. Vitale and his colleagues used two different models to assess whether traditional merger scenarios could create an event such as the unbalanced merger. No dice.
“No matter what we do, we cannot easily produce this event on these more common training channels,” Vitale said.
So the team turned to a process called hierarchical fusion, in which the result of a black hole fusion is fused again. And this time, the models seemed to make sense. “You do the math, and it turns out that the leftover black hole would have a spin very close to the full spin of this merger,” Vitale said.
Coincidentally, gravitational wave researchers published other research this week that also points to a hierarchical merger. On Wednesday (September 2), the scientists behind the LIGO gravitational wave detectors (short for “Laser Interferometer Gravitational Wave Observatory”) and Virgo announced that in May 2019, they had seen a black hole that was bigger of what scientists know how to form by stellar explosions. The suspicion is that this huge black hole, if not both original members of the event, was the result of a previous merger.
The scientists behind the new paper looking at the uneven collision suspect that hierarchical mergers cannot happen anywhere, but must occur in a relatively dense neighborhood, where black holes can easily interact with each other.
“This fusion must have come from an unusual place,” Vitale said. “As LIGO and Virgo continue to make new detections, we can use these discoveries to learn new things about the universe.”
The investigation is described in a paper published September 2 in the journal Physical Review Letters.
Email Meghan Bartels at [email protected] or follow her on Twitter @meghanbartels. Follow us on Twitter @Spacedotcom and on Facebook.
