Astronomers have watched a giant star blow up in a fiery supernova for the first time ever — and the spectacle was even more explosive than the researchers anticipated.

According to a new research published Jan. 6 in the Astrophysical Journal, scientists began observing the doomed star — a red supergiant called SN 2020tlf and located approximately 120 million light-years from Earth — more than 100 days before its last, cataclysmic collapse. During that time, the researchers witnessed the star erupt with dazzling bursts of light as massive globs of gas exploded from its surface.

A red supergiant star evolving into a Type II supernova, unleashing a powerful explosion of radiation and gas on its final breath before collapsing and exploding. (Photo courtesy of W. M. Keck Observatory/Adam Makarenko)

These pre-supernova fireworks surprised the researchers because earlier observations of red supergiants on the verge of exploding showed no signs of violent emissions, they said.

When big stars explode in popularity

In terms of volume, red supergiants are the biggest stars in the cosmos, measuring hundreds or even thousands of times the radius of the sun. (Despite their bulk, red supergiants are not the brightest or most massive stars in the universe.)

These huge stars, like our sun, generate energy by nuclear fusion of atoms in their cores. Red supergiants, on the other hand, can create considerably heavier elements than the hydrogen and helium that our sun burns. As supergiants burn increasingly heavy elements, their cores heat up and become more compressed. These stars eventually run out of energy by the time they begin fusing iron and nickel, their cores collapse, and they eject their gassy outer atmospheres into space in a catastrophic type II supernova explosion.

Scientists have spotted red supergiants before they go supernova and analysed the aftermath of these cosmic explosions, but they have never witnessed the entire process in real time until now.

The new study’s authors began studying SN 2020tlf in the summer of 2020, when the star flashed with dazzling flashes of radiation, which they later interpreted as gas erupting off the star’s surface. The researchers tracked the irritable star for 130 days using two telescopes in Hawaii: the University of Hawaii Institute for Astronomy Pan-STARRS1 telescope and the W. M. Keck Observatory on Mauna Kea. Finally, at the conclusion of that time, the star exploded.

The researchers saw evidence of a dense cloud of gas encircling the star at the moment of its explosion — likely the same gas that the star emitted in the preceding months. This shows that massive explosions began long before the star’s core disintegrated in the fall of 2020.“We’ve never confirmed such violent activity in a dying red supergiant star where we see it produce such a luminous emission, then collapse and combust, until now,” study co-author Raffaella Margutti, an astrophysicist at UC Berkeley, said in the statement.

According to the team’s findings, red supergiants suffer considerable changes in their interior structures, culminating in chaotic eruptions of gas in their final months before crashing.