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A blue flash from the spiral arm of a galaxy was picked up by telescopes around the world. The powerful burst was much brighter than any stellar explosion scientists had yet to see. The signal, procedurally labeled AT2018cow, has since been dubbed simply "the Cow" and has been catalogued as a bright, short-lived event of unknown origin.
A team from MIT found strong evidence for the signal's source. The scientists detected a strobe-like pulse of high-energy X-rays, as well as a bright optical flash. They traced hundreds of millions of X-ray pulse back to the Cow, and found that they occurred every 4.4 milliseconds for 60 days.
The X-rays must have come from an object with a mass less than 800 suns, based on the frequencies of the X-rays. A small black hole or a neutron star would be considered a compact object by astrophysical standards.
Their findings, published today in the journal Nature Astronomy, strongly suggest that AT2018cow was a product of a dying star that gave birth to a compact object in the form of a black hole or neutron star. The newborn object continued to eat the surrounding material, releasing an enormous burst of energy.
The lead author of the paper says that they have likely discovered the birth of a compact object in a supernova. This happens in normal supernovae, but we haven't seen it before because it's so messy. We think that this new evidence will lead to the discovery of baby black holes or baby neutron stars.
The core of the cow is what it is.
There were many "astronomical Transients" discovered in the year. The "cow" in its name is a random coincidence, and it refers to the first astronomical Transient discovered in 2018). The signal is among a few dozen known FBOTs, and it is one of only a few that have been observed in real-time. The powerful flash was detected by a survey in Hawaii, which immediately sent out warnings to observatories around the world.
"It was exciting because there was a lot of data piling up." The amount of energy was more than the typical collapse. The question was, what could be done to produce more energy?
Astronomers have come up with a number of explanations for the super-bright signal. It could have been a product of a black hole. It could have been caused by a black hole taking away material from a star. The data collected by optical telescopes hasn't resolved the source of the signal. He wondered if an answer could be found in the data.
The signal was close and bright in the X-rays, which got my attention. The first thing that comes to my mind is that some really energetic phenomenon is going to generate X-rays. I wanted to see if there is a black hole at the core of the cow.
Finding a pulse.
The team looked at the data from the X-ray telescope aboard the International Space Station. The Cow was first detected by optical telescopes about five days after it was found. The data was recorded in a publicly available archive, which was downloaded and analyzed by Pasham and his colleagues.
The team looked through the data to confirm that the emissions were not from other sources. They looked at the X-rays and found that the Cow was giving off a burst at a high Frequency of 225 hertz.
Pasham recognized that the pulse's Frequency could be used to calculate the size of the pulse. The speed of light can cover a distance in less than 4 milliseconds, so the size of the object cannot be larger than that. The object must be no larger than 1.3x108 centimeters, or roughly 1,000 kilometers wide.
The only thing that can be that small is a black hole or a neutron star.
The team calculated the amount of energy that must be no more than 800 solar mass.
The signal is not from an intermediate black hole.
The study shows that X-ray analyses of FBOTs and other ultrabright phenomena could be a new tool for studying infant black holes.
There's excitement when there's a new phenomenon that could tell something new about the universe. We have shown that we can study the pulsations in a way that is not possible in the optical. This is a new way to understand the newborn objects.
There is evidence for a compact object in the aftermath of the extragalactic Transient AT 2018cow. www.nature.com/articles/s41550-021-01524-8
Nature Astronomy journal has information.
A black hole or a dying star are likely to be the result of a super-bright stellar explosion.
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