Tracked down supernova predecessors

For the first time, astronomers will find potential precursors of a type 1c supernova

A hot, blue giant - that's what the predecessor of the Supernova Type 1c might look like. © NASA / ESA, J. Olmsted (STScI)
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Blue, extremely massive and very hot: astronomers have for the first time located the predecessor star of a type 1c supernova - the core collapse of a star without its shell of hydrogen and helium. Although this supernova occurs at 20 percent of the massive stars, astronomers have been puzzling over what the star of this explosion looks like for 20 years. Now they have first discovered recordings of such a Type 1c predecessor. How exactly he looks, but remains puzzling for now.

When massive stars reach the end of their life cycle, they explode in a supernova. White dwarfs in a binary system end up as Supernova Type 1a. However, most other stars undergo a nuclear collapse that creates a neutron star or a black hole. In some cases, however, the star loses its outer shell of hydrogen and helium before the explosion - astronomers call it a supernova of type 1c.

Search for the predecessor star

"The Type 1c supernovas occur at the most massive stars, " says first author Schuyler Van Dyk of the California Institute of Technology in Pasadena. "But astronomers have been trying in vain to find the predecessor of such a supernova for 20 years." The problem: many of these starbursts were too far away or occurred in the midst of bright star clusters, making their much fainter predecessor stars almost invisible to us.

But in 2017 astronomers came to the aid of a fortunate coincidence: a telescope once again observed a type 1c supernova. This time, however, it was "only" 65 million light-years away in a nearby spiral galaxy. To find the predecessor, the researchers now searched the archives of the Hubble Space Telescope for recordings of this celestial region. Their hope: Maybe the telescope had taken the predecessor star a few years before the supernova.

Hubble image of the spiral galaxy NGC 3938 and in the clippings the supernova as well as the predecessor candidate © NASA / ESA, S. Van Dyk (Caltech) and W. Li (University of California)

Hot, blue predecessor candidate

In fact, they found what they were looking for: in a Hubble photograph from 2007, they discovered a bright, bluish luminous object that was located exactly where the starburst exploded. "This is the first time an ancestor candidate has been identified for a supernova Type 1c, " says Van Dyk. "To find him is, so to speak, the main prize of such a search." Ad

Their discovery was confirmed by a second research team led by Charles Kilpatrick of the University of California at Santa Cruz. They were based on infrared images of the Keck Observatory in Hawaii in order to narrow down the location and possible properties of the supernova and thus of the predator. "The extremely high-resolution Keck images allowed us to pinpoint the location of the explosion with high precision, " says Kilpatrick. They, too, became involved in the same Hubble recordings.

Single star or heavy double?

However: What exactly is the hot, blue object is so far unclear. According to the spectral features and stellar models, the predecessor could be an extremely massive star of 45 to 55 solar masses. He would then have lost his hell of hydrogen and helium due to the strong star wind - which would be quite possible in view of a densely populated environment, as the researchers explain.

However, it would also be possible to have an unusually massive double star system, in which the larger partner weighs 60 to 80 solar masses, and the smaller about 48 solar masses. In this scenario, the larger star loses its shell due to the influence of gravity of its closely surrounding partner. A binary star system of two such heavy partners, however, contradicts the most common models.

Which scenario is right?

"We were surprised at how massive this predecessor seems to be, " says Van Dyk. "And most of all, we were struck by the possibility that such a massive binary star system might have spawned this supernova." Even though newer models definitely see double stars as the originators of such explosions, they are assuming much more mundane systems as the astronomers explain.

"Finding out which of these scenarios is right for the Supernova Type 1c will crucially affect our understanding of star formation and stellar evolution, " said co-author Ori Fox of the Space Telescope Science Institute in Baltimore. "And these are questions that concern not only supernova researchers, but all astronomers." So far, however, is not even excluded that the bright, blue-luminescent object is actually a star cluster, in which the actual Vorg nger hidden.

Solution of the riddle in the coming years

Those who are really behind the supernova Type1c, could but in the coming years kl ren. Because now that the position of the Vorg nger candidate is clear, the astronomers want to keep an eye on the location of the explosion. Because the afterglow of the explosion becomes weaker in the course of time and then clears the view of what remained with the supernova.

"An important test will be, in a few years, when the supernova fades, to continue observing this location with the Hubble Telescope or the James Webb Space Telescope, " the researchers say. "If the binary star models are correct, a bright companion star would still have to be visible at the supernova site." (The Astrophysical Journal, 2018; a href = "https://doi.org/10.3847/1538-4357 / aac32c "target =" _ blank "> doi: 10.3847 / 1538-4357 / aac32c)

(Keck Observatory, Caltech, NASA, 16.11.2018 - NPO)