Scientists say they finally have an explanation for a mystifying, bright blue light that came from deep in space.
Three years ago, astronomers were stunned to see a bright blue flash that came out of the spiral arm of a distant galaxy, some 200 million light-years away.
The initial detection of the event known as AT2018cow happened in June 2018, when it was seen by a survey in Hawaii, which quickly sent out global alerts to tell other telescopes to look towards it. They saw a bright flash 100 times brighter than the usual supernova, the brightest explosion humanity has seen.
It looked like a supernova, but it was even brighter and faster than those already extreme events. Scientists struggled to explain it, and it became known as a fast blue optical transient, or FBOT, with no explanation of how it happened.
Further detail on the event only seemed to make it more puzzling. Scientists found that it consisted not only of the bright flash of light, but also pulsing and powerful X-rays, with hundreds of millions of such pulses being traced back to the same object.
Those pulses happened regularly, every 4.4 miliseconds, over a period of 60 days.
Scientists used those pulses to calculate that the source of the X-rays must be no more than 1,000 kilometres wide, and have a mass less than 800 suns. That would seem to suggest that it is something compact, such a small black hole or a neutron star.
As such, it appears that the mystifying flash probably happened as a star was dying – as it collapsed, it gave birth to a baby black hole or neutron star. That went onto eat the material that surrounded it, swallowing up the star, releasing intense bursts of energy as it went.
That is the conclusion presented in a new paper, ‘Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow’, published in Nature Astronomy.
“We have likely discovered the birth of a compact object in a supernova,” says lead author Dheeraj “DJ” Pasham, a research scientist at MIT. “This happens in normal supernovae, but we haven’t seen it before because it’s such a messy process. We think this new evidence opens possibilities for finding baby black holes or baby neutron stars.”
Previous attempts to explain the flash have suggested that it could be a black hole being born in a supernova, or a star ripping the material from another passing star. But astronomers have never been able to satisfactorily explain the flash using only optical data – which led the researchers behind the new paper to look at the X-ray energy too.
That led them to examine the regular pulses, which could be used to learn more about the object that was sending them. That ruled out an intermediate black hole and led scientists to the current explanation, they said.
The same techniques could be used to help better understand other fast blue optical transients in the same family, scientistssay.
“Whenever there’s a new phenomenon, there’s excitement that it could tell something new about the universe,” Pasham says. “For FBOTs, we have shown we can study their pulsations in detail, in a way that’s not possible in the optical. So, this is a new way to understand these newborn compact objects.”
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