Radio signal reveals supernova origin for the first time

Researchers have been trying for decades to use radio signals to detect the origins of a special type of supernova, and now they've managed to pull it off.
John Loeffler
A supernova
A supernova

Soubrette/iStock 

Supernovae are the most powerful and energetic explosions in the universe, and scientists have been trying for decades to use radio signals to detect the origin of special types of supernovae for decades to no avail. Now, researchers at Stockholm University have done just that, giving astronomers a new way to examine these stellar explosions.

A 2020 supernova designated SN 2020eyj is of a special class of supernovae known as a Type Ia supernova. These kinds of supernovae are almost always the same brightness so they are used by astronomers to help measure distances at a cosmological scale, as well as the expansion of the universe.

“While normal Type Ia supernovae appear to always explode with the same brightness, this supernova tells us that there are many different pathways to a white dwarf star explosion”, Joel Johansson, of Stockholm University's (SU) Department of Physics, said in a statement.

Though SN 2020eyj was discovered through traditional means in 2020, by finding its radio signal signature, the finding — described in a new paper published in Nature this week — helps explain the mechanism behind how white dwarfs explode into Type Ia supernovae.

Typically, a white dwarf on its own is stable, but it is incredibly dense so it can barely support its own weight. In a binary star system where one of the two stars is a white dwarf, it can accrete material from a companion star onto itself.

It is theorized that once enough material has been accreted onto the white dwarf from the donor star, it crosses a threshold where it can no longer support itself and the new material, causing it to collapse in on itself and triggering a highly energetic supernova.

White dwarf interaction with donor material produces a telltale radio signal

While much of the donor material in Type Ia supernova accretes to the white dwarf, it is suspected that not all of it gets pulled onto the white dwarf. It's theorized that a cloud of circumstellar material from the donor star will form around the two stars.

When the white dwarf explodes in a supernova, it has long been suspected that it should create shockwaves in this cloud, which would excite the atoms in the cloud and produce radio waves that astronomers will be able to detect. This is principally what the researchers found in SN 2020eyj.

One of the key insights for finding the radio signal came from the study of the material surrounding the explosion source.

“Once we saw the signatures of strong interaction with the material from the companion we tried to also detect it in radio emission”, said the paper's lead author, Erik Kool, a post-doctoral researcher at the SU's Department of Astronomy. “The detection in radio is the first one of a Type Ia supernova – something astronomers have tried to do for decades.”

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