In 2018, astronomers observed the first supernova explosion of a new class dubbed “The Cow”. Today, a team reports having discovered news of these astonishing explosions. The brightest ever seen in x-rays.
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[EN VIDÉO] Crab Nebula: relive its terrible supernova explosion Here is, replayed, the explosion of the supernova that occurred in the year 1054 in the constellation Taurus. The Earthlings of the time saw a new new star sparkle day and night for several months. Today, its remains, dubbed the Crab Nebula, continue to expand. Here we see them observed by five large instruments, working in different wavelengths, in false colors.
Until then, the astronomers had not observed more than four. They’ve just got their hands on a fifth of this new class of stellar explosions they’ve dubbed “The Cow” – understand ” the cow“. Remarkable explosions, because more brilliant – and shorter – than those of classic supernovae . And this one – named AT2020mrf – has one more particularity: that of having been spotted not in the spectrum visible, but thanks to an impressive episode in X-rays.
After data analysis, it even turns out that AT2020mrf emitted 200 times more X-rays than AT2018cow, the first of the type explosions “The Cow” discovered in 2018. Never seen before. “I redid the analysis several times because I could not believe it”, even confides Yuha, Yao, researcher at Caltech University (United States), in a communicated.
An “active engine” behind the star explosion
Remember that when a massive starexplodes, it leaves behind, either a black hole , be one star neutrons. Star remains generally relatively inactive. But according to the researchers, the events “The Cow” must hide like a “Central motor” which feeds intense and continuous X-rays. “It probably has something to do with the type of progenitor star”, suggests Yuha, Yao.
The large amount ofenergy released and the rapid X-ray variability observed in AT2020mrf provide evidence solidthat the nature of this “Central motor” could be a very active black hole. Or a rapidly spinning neutron star that astronomers call a magnetar . But to understand why a “Central motor” so active, researchers will certainly still have to study more of these explosions. Because this class of supernova “The Cow” seems to want to turn out to be more diverse than astronomers had imagined.
Astronomers have discovered a new class of cosmic explosions
In 2018, the observation of a flash very bright some 200 million light years from Milky Way had confused the astronomers. A transitory phenomenon which seemed isolated. But researchers have just identified two similar ones. Enough to form a new class of cosmic explosions.
Article by Nathalie Mayer published on 05/28/2020
The story begins in June 2018, when astronomers witness a surprising cosmic explosion some 200 million light years from the Milky Way. Baptized AT2018cow and quickly nicknamed “The Cow” – “the cow” -, this strange transient phenomenon is observed from the ground and from space. It is brighter than a supernova. And its light curve evolves differently. A mystery.
Since then, astronomers have discovered two other similar transient phenomena. The first, also observed in 2018, occurred some 3.4 billion light years away. He is nicknamed “The Koala” – and more scientifically, ZTF18abvkwla. His show radioappears as powerful as that of a gamma-ray burst .
It took us two years to figure it out.
The second transient phenomenon similar to “The Cow” was surprised a few years ago, in 2016, in a galaxyabout 500 million light years away, and researchers call it CSS161010. “It was so unusual that it took us two years to figure it out”, says Raffaella Margutti, researcher at the university Northwestern, in one press release National Radio Astronomy Observatory (NRAO, United States). It has indeed propelled into space, a quantity “Unexpected” of gases and particles at more than 55% of the speed of light .
Astronomers know of phenomena capable of ejecting matterat a speed close to that of light. Gamma-ray bursts and neutron star collisions. But still in very small quantities. Of the order of a millionth of the mass of Sun . “Here, it is a question of 1 to 10% of the mass of our Sun”, remarks Deanne Copejans, researcher at the university Northwestern, in one communicated. The proof, according to the researchers, that we are dealing here with a new class ofcosmic explosions baptized Fast Blue Optical Transients (FBOTs) – “Blue transient optical phenomenon” – to give an account of the speed of the phenomenon, a few days, and its peak of brightness achieved in the field of wavelengthsblue.
End-of-life stars in dwarf galaxies
Astronomers believe that at the starting point of FBOTs, there is a massive star at the end of its life . Recall that the explosion of a supernova at collapse heart produces a spherical wave of matter which propagates in space. If a disc of matter forms around the neutron star or the black hole born from the explosion – “The key ingredient” according to the researchers – and that it propels jets of narrow material at a speed close to the speed of light, these jets may be at the origin of what astronomers call startle gamma. To designate this disc and these jets of matter, the researchers speak of ” motor “.
And FBOTs also seem to have such a ” motor “. But made up of a materialthick, lost by the star before its explosion. Maybe because of a companion binary. It would therefore be when this material is struck by the wave of the explosion that the luminosity of the phenomenon reaches its climax. The same applies to transmission in the radio domain.
Astronomers believe that the stars that cause these new kind of cosmic explosions are different from those that produce gamma-ray bursts. And since the three phenomena of this type observed up to now are located in dwarf galaxies , they imagine that it is these dwarf galaxies that allow this type of stellar evolution. Stars poor in elements other thanhydrogen and thehelium– as we find in this type of galaxies – indeed lose less material during their life. They are therefore likely to produce more massive explosions when their end comes.
The researchers also warn that the phenomenon could result from stars jagged by medium-sized black towers. To be sure, you will need to observe a few more FBOTs.
The phenomenon would not be so rare. Astronomers suspect that other FBOTs are hiding in their data. “We were able to recognize them as something different, somewhat bizarre supernovae, but since we only had observations at low speed and in the field of optics …”, remarks Raffaella Margutti, in the university press release Northwestern. Indeed, the ephemeral side of the phenomenon requires high-speed observations, sweeping large expanses of sky. And if the field of optics can provide information on moving particles ” slowly “ – at some 10,000 km / s all the same – we must have recourse to X-rays or radio waves to hope to form a more complete image of these powerful explosions.
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