Extremely unusual supernova discovered that exploded twice

Generally, when a star enters a phasesupernova, it explodes and ... in fact, it comes to an end. However, a new discovery by astronomers may make us rethink our understanding of how stars can perish. Scientists discovered a star that entered the supernova phase, exploded, somehow managed to survive this event, and then, after 60 years, exploded again. For space researchers, this turn of events was extremely unusual. Just because it should not be.

Supernova, dubbed iPTF14hls, wasdiscovered in 2014 and at first glance it seemed to researchers a very ordinary class II-P supernova. The supernovae of this class are the nuclei of massive stars that turn into a neutron star and create a powerful shock wave that passes through its outer shell, rich in hydrogen, which is released into space. The ejected matter is ionized by the shock wave, and later it cools and recombines.

Marked spectroscopic featuresThe supernova iPTF14hls seemed completely identical for class II-P supernovae. But then, a few months later, she showed behavior that other supernovae did not usually show — she again lit up, as they say.

For a 600-day period of observation of her, shedim several times, and then again became brighter. In less than three years, at least 5 such cases have been recorded. Usually supernovae reach a peak of maximum brightness, shine like this for several months, and then begin to fade constantly. However, when scientists from the Las Cumbres Observatory (USA) returned to the study of archived data, they discovered something surprising - the same supernova exploded in 1954.

Graph of brightness changes (in billions of suns) of the supernova iPTF14hls (marked with a yellow line) in comparison with the behavior of a regular supernova (marked with a blue line) over a 600-day period

“This supernova crosses out everything we knewabout these objects. This is the biggest mystery I’ve encountered in nearly a decade of stellar collapse research, ”commented astronomer Yair Arkavi of the University of California, Santa Barbara and researcher at Las Cumbres observatory.

In the journal Nature, researchers citecalculations according to which the initially supernova iPTF14hls was a larger star, at least 50 times more massive than our Sun and, most likely, much larger.

"In fact, the supernova iPTF14hls maybe the biggest star explosion ever seen, ”said researcher Lars Bildsten, director of the Cavlee Institute of Theoretical Physics at the University of California.

The astronomer believes that a possible explanation forthe supernova iPTF14hls could serve as the fact that it is the so-called pulsating para-unstable supernova, which would make it the first of its kind object of the type that was actually observed. This is the event of the ejection of a huge amount of stellar matter, which at first glance may seem like a supernova, but at the same time not destroying the star.

According to scientists, this phenomenon is possibleonly with stars with a mass 95-130 times the size of the sun. During these emissions, the star spits out its outer layer, due to which it is reduced by 10-25 solar masses. This can be repeated until the star ultimately collapses into a black hole. But this is only an assumption. The star Eta Kiel was considered as an earlier candidate for the role of a pulsating para-unstable supernova. According to scientists, 1843 ejection of matter occurred on it, however, researchers have not yet been able to confirm that the star belongs to this class.

“Similar starbursts could be expected intime of the early Universe, but now definitely not. It is as if we discovered today a real living dinosaur. If they found one, they would probably ask themselves: is this a dinosaur? ”Comments Andy Howell of the University of California, who leads the supernova research and study team.

It would seem that the riddle is close to a solution. But everything is not as simple as we would like. The fact is that the hypothesis does not take into account the presence of hydrogen in a pulsating para-unstable supernova. After the explosion in 1954, the supernova iPTF14hls retained several tens of solar masses of hydrogen in its shell. In addition, in a later supernova explosion, energy was present several orders of magnitude higher than described in the hypothesis of pulsating para-unstable supernovae. Two conclusions can be drawn from this: either the iPTF14hls is indeed a pulsating para-unstable supernova, but at the same time extremely unusual, or it is some completely different kind of supernova that has never been seen before.

The research team continues to monitor this supernova and hopes that after a while it will still be able to find the right answer.

“This is one of those types of events over which you canliterally break your head. At first we thought it was a completely ordinary and completely unremarkable object. Then it became brighter, and this brightness did not change from month to month, ”says researcher Peter Nugent of the Lawrence Berkeley National Laboratory.

“Having collected all the data from our observations from"We can get to the bottom of the Palomar Observatory, the Keck Observatory, the Las Cumbres Observatory, and even the images obtained in the framework of the 1954 Palomar Review."

“I would very much like to find at least one more similar object,” the scientist added.