Stars can go supernova in many different ways, and based on the light that supernovas emit, researchers can work out their progenitor stars. But one specific kind of supernova, Type Ic, has remained a mystery. The progenitors of this type of supernova are supposed to lack helium and hydrogen and be very massive. But astronomers had never seen such stars. Until now.
In 2017, a (relatively) nearby star exploded as a Type Ic supernova. Two teams of researchers used the extensive Hubble star catalog to hunt down the progenitor and were able to find it. Supernova 2017ein was likely produced by a blue star weighing many dozens of time the mass of the Sun.
The first study came out in June and was published in The Astrophysical Journal. The supernova took place in galaxy NGC 3938, which is roughly 65 million light-years away. The team found Hubble observations of the galaxy going back to 2007.
“Finding a bona fide progenitor of a supernova Ic is a big prize of progenitor searching,” lead author of this study, Schuyler Van Dyk of the California Institute of Technology (Caltech) in Pasadena, said in a statement. “We now have for the first time a clearly detected candidate object.”
The second paper was published in the Monthly Notices of the Royal Astronomical Society a few weeks ago. The results are consistent with the first study but add a new dimension to it. The second team observed the supernova in infrared light which allowed them to pinpoint exactly where the progenitor was.
“We were fortunate that the supernova was nearby and very bright, about five to 10 times brighter than other type Ic supernovas, which may have made the progenitor easier to find,” added the second team's leader Charles Kilpatrick from the University of California, Santa Cruz.
“Astronomers have observed many type Ic supernovas, but they are all too far away for Hubble to resolve. You need one of these massive, bright stars in a nearby galaxy to go off. It looks like most type Ic supernovas are less massive and therefore less bright, and that’s the reason we haven’t been able to find them.”
Theoretical models assume that Type Ic progenitors are at least 30 times the mass of the Sun, but the one observed here weighs between 45 and 55 times our star at least. That’s the case if it’s an isolated star. If it has a companion, it could be up to 80 times the mass of the Sun. Understanding which of these scenarios is correct is important for understanding how stars die in such a way but also the distribution of masses when stars are born.
In two years' time, astronomers will be able to confirm if this star really was the true progenitor. They need to wait for the supernova to fade out first.