Here is the most powerful supernova in X-rays ever observed

Until then, the astronomers had seen no more than four. They’ve just gotten their hands on a fifth of this new class of stellar explosions they’ve dubbed “the Cow” — understand ” the cow». Remarkable explosions, because brighter — 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 of the visible, but thanks to an impressive episodein the 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. Unheard of. “I redid the analysis several times because I couldn’t believe it”, even confides Yuha, Yao, a researcher at Caltech University (United States), in a communicated.

An “active engine” behind the stellar explosion

Remember that when a massive starexplodes, she leaves behind her, either a black hole , be one star neutrons. Usually relatively inactive star remnants. But according to the researchers, the events “the Cow” have to hide like a “mid-engine” which feeds an intense and continuous X-radiation. “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 seen in AT2020mrf provide evidence solidthat the nature of this “mid-engine” could be a very active black hole. Or a rapidly rotating neutron star that astronomers call a magnetar . But to understand why a “mid-engine” as active, it will certainly be necessary for the researchers to study other 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 the Milky Way baffled astronomers. A transient phenomenon that seemed isolated. But researchers have just identified two similar ones. Enough to form a new class of cosmic explosions.

Article of Nathalie Mayer published on 05/28/2020

The story begins in June 2018, when astronomers witness a startling cosmic explosion some 200 million light-years from the Milky Way. Dubbed AT2018cow and quickly dubbed “the Cow” — “the cow” — this strange transient phenomenon is observed from the ground and from space. It’s 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 burst .

The second transient phenomenon similar to “the Cow” was surprised a few years earlier, in 2016, in a galaxyabout 500 million light-years away, and researchers call it CSS161010. “He was so unusual that it took us two years to figure it out”, says Raffaella Margutti, a researcher at the university Northwestern, in one statement of National Radio Astronomy Observatory (NRAO, USA). He 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 matter at a speed close to that of light. Gamma-ray bursts and neutron star collisions. But still in very small quantities. On the order of one millionth of the massfrom Sun . “Here, we are talking about 1 to 10% of the mass of our Sun”, notes Deanne Copejans, a 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 account for the rapidity of the phenomenon, a few days, and its peak 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 end of life . Remember that the explosion of a supernova at collapse of heart produces a spherical wave of matter which propagates in space. If a disk of matter forms around the neutron star or black hole that was born from the explosion — “the key ingredient” researchers say — and propels narrow jets of material at near the speed of light, those jets may be causing 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 ” motor “. But consisting of a materialthick, lost by the star before its explosion. Maybe because of a girlfriend binary. It would therefore be when this material is hit 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 at the origin of 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 localized 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 found in this type of galaxy — indeed lose less matter during their lifetime. They are therefore likely to produce more massive explosions when they come to an end.

The researchers also warn that the phenomenon could result from stars being shredded by medium-sized black towers. To be sure, you will have to observe a few more FBOTs.

The phenomenon would not be so rare. Astronomers suspect that other FBOTs lurk in their data. “We were able to recognize them as something different, kinda weird supernovae, but since we only had low-rate observations and in the field of optics…”, remarks Raffaella Margutti, in the press release of the university 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 –, it is necessary to have recourse to X-rays or radio waves to hope to form a more complete image of these powerful explosions.