Progenitor Stars are so massive that they can explode in a supernova despite losing their outer layers.

A supernova is an event that follows the death of specific types of stars. It radiates more heat energy than our sun will in its entire lifetime. The primary source of heavy metals is also labeled as the largest explosion that can take place in space. Some of the supernovae, like Type Ic, are much more challenging to study than the others. Recently, astronomers were able to unveil the long-lasting mystery of one such supernova as they found that the outer layers of its massive stars were stripped off, even before the detonation.

The stars involved in this kind of a supernova are among the most massive known to humanity. According to an estimate, they are at least 30 times heavier than our sun. That’s the reason why they are expected to stay bright even after losing some material in their dying moments. Despite that, scientists were unable to capture a pre-explosion image of any of these stars until 2017, when they studied a nearby star which experienced a Type Ic supernova. The Hubble Space Telescope of NASA provided the images for this supernova, called SN 2017ein. The event took place near the center of NGC 3938, a spiral galaxy which is at a distance of 65 million light-years from the Earth.

Two individual teams examined the data from the archive of Hubble and found pre-explosion pictures of the star that were taken in 2007. Scientists are quite hopeful that this potential discovery will offer some useful insights about stellar evolution. Schuyler Van Dyk, the Lead Researcher of one of the teams, was delighted about the finding and regarded it as a big prize of Progenitor Searching. He mentioned that they finally have a clearly detected candidate object that will prove instrumental in future studies. Similarly, Charles Kilpatrick of the University of California, who led the second team, mentioned the significance of the discovery by saying,

“We were fortunate that the supernova was nearby and very bright, about 5 to 10 times brighter than other Type Ic supernovas, which may have made the progenitor easier to find. 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.”

The analysis of both the teams concluded with two possible outcomes. The first one of them suggests that the progenitor could be a single star having a mass of 45 to 55 suns. On the other hand, it was a massive binary-star system in which one of the stars weighs somewhere around 60-80 solar masses while the relatively smaller star is 48 times more massive than our sun. In this system, both the stars orbited around each other and their interaction deprived the larger one of its Hydrogen and Helium layers. This eventually ended with a massive explosion. Despite the proposition, Van Dyk mentioned that the theory of binary-star system was quite surprising for them. He said,

“This is not what we would expect from current models, which call for lower-mass interacting binary progenitor systems.”

Initially, researchers proposed that hefty stars release Hydrogen and Helium, in form of a strong wind, before exploding in a supernova. However, failure to find an ideal progenitor star forced them to come up with another theory. That’s when the idea of close-orbiting, binary stars was floated around the table as the stripped star is still massive enough to detonate as a Type Ic supernova. Ori Fox, a Member of the Van Dyk’s team who is associated with the Space Telescope Science Institute, elaborated that in the following words:

“Disentangling these two scenarios for producing Type Ic supernovas impacts our understanding of stellar evolution and star formation, including how the masses of stars are distributed when they are born, and how many stars form in interacting binary systems. And those are questions that not just astronomers studying supernovas want to know, but all astronomers are after.”

In spite of all the findings, the researching teams cannot confirm the identity of the source until the supernova fades, which is about two years away. Either Hubble or James Webb Space Telescope will be used for checking the status of the candidate progenitor star. The light from surrounding stars will also be separated to ensure an accurate measurement of the object’s mass and brightness.