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What was the Cow, the explosion a hundred times more brilliant than a supernova?

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MadridUpdated:13/01/2019 02:11 am

Astronomers from all over the world were amazed last June 17, when a brief and unusual flare appeared with a violence unusual in the night sky. During three days, the explosion of light, listed as AT2018 cow and popularly known as the Cow by the final letters of his name (cow is “cow” in English), was between ten and one hundred times brighter than the supernova typical. Came out of nowhere, dazzled us, and in the following months it was fading.

The event took place inside or near a galaxy forming stars known as CGCG 137-068, located about 200 million light-years away in the constellation of Hercules. Different to any outbreak celeste ever seen, scientists do not yet agree on its origin.

Two teams have published a series of articles that provide possible explanations of what is what came out of the depths of space. One holds that it is a monstrous black hole that destroys a star to your step. The second raises the possibility that it is a supernova, a stellar explosion, which gave rise to a black hole or a neutron star. The hypotheses have been presented at the annual meeting of the Astronomical Society American held these days in Seattle.

The theory of the star shattered

The first explanation of the Cow points out that a star could be torn apart at the approach of a black hole, and it is decomposed in a gas stream. The tail gas stream is ejected from the system, but the anterior edge rotates around the black hole, it collides against itself and creates a cloud of material elliptical. According to the researchers, who used data from infrared radiation to gamma-ray space telescope, Swift and other observatories, this transformation explains the behavior of the light signal. To reach this conclusion, they used data from the telescope Swift of NASA and other observatories.

“We’ve never seen anything exactly like the Cow, is very exciting,” acknowledges Amy Lien, of the University of Maryland and the Goddard Space Flight Center of NASA in Greenbelt, whose theory will appear in a future edition of the journal Monthly Notices of the Royal Astronomical Society. [You can already see in Arxiv.org] As she explains it, the star was a white dwarf, a stellar remnant about the size of Earth that marks the end state of stars like our Sun. The researchers also calculated that the mass of the black hole varies from 100,000 to 1 million times that of the Sun, almost as large as the central black hole of its host galaxy. It’s unusual to see black holes of this scale outside of the center of a galaxy, but it is possible that the Cow will produce in a satellite galaxy near or in a star cluster globular star whose stellar populations older may have a greater proportion of white dwarfs that galaxies on average.

“The Cow produced a large cloud of debris in a very short time,” says the lead author of the study, Paul Queen, astrophysicist at University College London (UCL). “To destroy a larger star to produce a cloud, as this would require a black hole larger, it would result in an increase in brightness more slowly and take more time to consume the rubble.”

Sloan Digital Sky Survey
Sloan Digital Sky Survey

The hypothesis of the supernova

A different team was able to collect data about the Cow in a range even larger range of wavelengths, ranging from radio waves to gamma rays. Based on these observations, suggests that a supernova could be the source of the Cow. When a massive star dies, it explodes as a supernova and leaves behind a black hole or an object incredibly dense called a neutron star. The “Cow” could represent the birth of one of these remains stellar.

“We believe that this was a special case, and that we may have observed, for the first time, the creation of a compact body in real time, “says Raffaella Margutti, an astrophysicist at Northwestern University in Evanston, Illinois, and lead author of a study published in the journal “the Astrophysical Journal”.

Normally, the cloud of debris expanding from a supernova blocks any light of the compact object in the center of the explosion. Due to the emission of X-rays, Margutti and his colleagues suggest that the star original in this scenario may have had a mass relatively low, producing a cloud of debris comparatively thin through which they could escape the X-rays from the central source.

“If we are seeing the birth of a compact object in real-time, this could be the beginning of a new chapter in our understanding of stellar evolution”, indicates Brian Grefenstette, scientific instruments of NuSTAR at Caltech and a coauthor of the study. “We observed this object with many observatories in different and, of course, the more windows are opened to an object, the more you can learn about it. But, as we saw with the Cow, that doesn’t necessarily mean that the solution is simple”. Perhaps a new Cow can clarify the mystery.

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