Unusually bright and large flash AT2018cow, unofficially known as “the cow”, could be the result of the explosion of a massive star and subsequent birth of a black hole. To such conclusion scientists came by examining the galaxy, where the event occurred, with the help of the Chilean telescope Very Large Telescope (VLT). An article about the results of the observations, accepted for publication in Monthly Notices of the Royal Astronomical Society, Preprint available on the website arXiv.org.
In June 2018, the telescope system ATLAS registered in the constellation of Hercules, an unusual outbreak. Its peak brightness exceeded the peak brightness of the supernova in the usual dozens of times, and reached her just two and a half days — while a supernova it takes weeks. Initially, astronomers assumed that the event was supposed to happen inside the milky way, but later it was found to correlate with galaxy CGCG 137-068, the light from which came to us 200 million years. The flash attracted the attention of scientists all over the world and in the next few days 18 large telescopes watched “cow” in different ranges of electromagnetic waves. It turned out that her temperature is greater than 8.9 thousand degrees Celsius, and it expands with the velocity of 20 thousand kilometers per second.
A long time nature AT2018cow remained unknown. Astronomers have proposed two main mechanisms that could explain observed features or outbreak occurred as a result of the explosion of a massive star, or by the absorption of small stars black hole — but still it was not clear which of them is preferable.
Joseph Lyman from the University of Warwick, together with colleagues conducted observations of the galaxy CGCG 137-068 using the VLT interferometer. Astronomers searched for signs of the presence of a black hole in the field where there was flash, but instead discovered molecular cloud in which strong emerging young luminaries of the age of the stellar population of the region amounted to only a few tens of millions of years. This pattern is considered typical for a supernova with collapsium core, when as a result of rapid compression and subsequent powerful explosion of a massive star, a dramatic increase of the luminosity. Thus, depending on the original size of the star remains core to form either a neutron star or a black hole.
The hypothesis is also corroborated by the fact that AT2018cow stayed hot after the initial explosion longer than most supernovae. According to scientists, this means that after the explosion of a star probably held some object that was active and continued to heat the area — for example, it could be a black hole. This fact could explain the observations, which showed that in the flash space was thrown not so much substance. It is, according to the researchers, could be immediately absorbed by the newborn black hole.
Flash like AT2018cow are rare — they make up less than percent of all supernovae. Their search is complicated because of the speed events, but if astronomers can find more such explosions, they can determine what lies at their basis.
In the past, astronomers reported on the discovery of other unusual supernovae. Its brightness will not fall for more than six days.