The astronomers were able for the first time witness the transformation of a star into a black hole or a neutron star, according to the portal Space.com. The signal is very powerful emission of radiation, jokingly nicknamed by the scientists “The Cow” (“Cow”), was first recorded in June last year. Initially, the experts considered that saw the emergence of a supernova. However, almost immediately it became clear that some features of the signal have never been observed.
In the work, which will soon be published in the Astrophysical journal, scientists talk about the first 100 days of observations of the new object.
“Based on observable evidence in x-ray and ultraviolet ranges of the spectrum, our assumption immediately was connected with a cosmic cataclysm. Among the first assumptions was the emergence of unusual supernovae, or absorption by a black hole a white dwarf,” says Professor of physics and astronomy, Raffaella, Margutti from northwestern University in Chicago (Illinois, USA).
White dwarfs are compact stars with masses comparable to or larger than the mass of the Sun, but a radius 100 times smaller.
“However, further observations of the phenomenon in other spectrum bands has led us to a different conclusion. We are inclined to believe that had the opportunity to see the birth of a black hole or neutron star. Theories about black holes and neutron stars we are aware that these objects are formed immediately after the death of massive stars, but we have never seen before the very moment of the origin of these objects,” adds the scientist.
The phenomenon under discussion, the designation AT2018cow (or just “The Cow”), was first recorded by the ATLAS telescope, located in Hawaii. It happened about 200 million light-years from us, which by cosmic standards is not very far. Of even greater interest is fueled by the fact that the phenomenon was very bright – about 10-100 times brighter than an ordinary supernova explosion — as well as very short. Peak brightness occurred just a few days, compared to the normal two weeks.
“All this phenomenon is very surprised and interested, as was very unusual and at the same time happened pretty close by cosmic standards,” says the Professor of physics and astronomy Ryan Chornock from Ohio University, is co-author of a published study.
Image of the phenomenon AT2018cow and galaxy CGCG 137-068 in which it was received August 17, 2018 by using one of the spectrographs Observatory Keck
Then astronomers from all over the world began to follow him through different telescopes. For example, the command, Margutti decided to conduct monitoring of the source using the space Observatory NASA’s NuSTAR working in x-ray range. In addition, the work was connected to the space telescope ESA INTEGRAL (Gamma-Ray Astrophysics Laboratory), working with gamma rays and XMM-Newton, working with high-energy radiation, as well as several ground-based observatories.
Chemical analysis of the phenomenon showed that the radius of the source of hydrogen and helium, not what scientists expected to see. Usually when stars become supernova, at this point, they already have time to develop the reserves of these elements during fusion reactions.
The observed high-energy radiation, scientists also seemed very unusual. The NuSTAR telescope, through which scientists began to track the subject a little more than a week since first opening, showed that the radiation source “Cow” has suddenly become a much brighter range of high-energy x-ray radiation. According to astronomers, is a high-energy radiation most likely comes from the region very hot and dense plasma surrounding the source.
Since the monitoring project was carried out over a long period of time, the data also showed gradual loss of high-energy x-ray signal. Scientists believe it was caused by so-called processed radiation – radiation from a source interacts with the material expelled by the explosion. As soon as material is removed from the center of the explosion, the signal gradually decreases and eventually disappears completely.
The team of Margutti at this point makes two assumptions. “Cow” can be either magnetized neutron star, rotating with a speed of about 1000 revolutions per second, or the object previously belonged to young, hot and very bright stars — the blue supergiants — subsequently turned into a black hole.
Under the second option, according to the scientists, the interior of the star might turn into a black hole, while the outer layers have not yet been in her tightened. The growth of the black hole she could lose some of its mass in the form of emitted neutrinos. These neutrinos could capture a part of the particle outer shell of the star to the moment she fell into a black hole, and form around it the accretion disk.
At the moment, not everyone agrees with the interpretation of the observations of the team, Margutti. According to some scholars, if the center of the “Cow” is indeed a neutron star with a strong magnetic field, the object will be able to generate emissions of x-rays for a very long years. Black hole, in turn, will not show this behavior, so longer observations will allow us to finally determine the nature of the observed phenomenon. In fact these scientists are planning to do.