Gone in a flash: supernova burns up in just 25 days

Astronomers have witnessed a blazing supernova explosion that faded away 10 times faster than expected.

A supernova is the violent death of a massive star, typically occurring when it exhausts its fuel supply and collapses under its own weight, generating a powerful shockwave that blasts light and material out into space. 

Supernovae often blaze so brightly that they briefly outshine all the other stars in their host galaxy. They show off for months on end — in 1054, a supernova could be seen during the day for three weeks and only disappeared completely after two years. Its remnants are known as the Crab Nebula. 

Now an international team of astronomers, led by Armin Rest from the Space Science Telescope Institute in Baltimore, US, has observed a supernova that rapidly soared to its peak brightness in 2.2 days then faded away in just 25.

“When I first saw the Kepler data, and realised how short this transient is, my jaw dropped,” recalls Rest.{%recommended 1785%}

The supernova, dubbed KSN 2015K, is part of a puzzling class of rare events called Fast-Evolving Luminous Transients (FELTs). FELTs don’t fit into existing supernova models and astronomers are still debating their sources. Previous suggestions include the afterglow of a gamma-ray burst, a supernova turbo-boosted by a magnetically-powerful neutron star, or a failed example of special type of binary star supernova known as a type 1a. KSN 2015K is the most extreme example found so far.

In a paper published in the journal Nature Astronomy, the team says that KSN 2015K’s behaviour can most likely be explained by its surroundings: the star was swathed in dense gas and dust that it ejected in its old age, like a caterpillar spinning a cocoon. When the supernova detonated, it took some time for the resulting shock wave to slam into the shell of material and produce a burst of light, becoming visible to astronomers.

KSN 2015K was captured by NASA’s Kepler Space Telescope, which is designed to hunt for planets by noticing the tiny, temporary dips in light from far-away stars when planets pass in front of them. This exact skill is also useful in studying supernovae and other brief, explosive events.

“Using Kepler’s high-speed light-measuring capabilities, we’ve been able to see this exotic star explosion in incredible detail,” says team member Brad Tucker, an astrophysicist from the Australian National University.

Co-author David Khatami from the University of California, Berkeley, US, adds that this is the first time astronomers can test FELT models to a high degree of accuracy. “The fact that Kepler completely captured the rapid evolution really constrains the exotic ways in which stars die,” he says.

Australian researchers and facilities were also key to this discovery. Follow-up observations were made with the SkyMapper telescope at Siding Spring Observatory, and then processed by the National Computational Infrastructure at the Australian National University in Canberra.

Tucker says that by learning more about how stars live and die, astronomers can better understand solar systems as a whole, including the potential life on orbiting planets.

He concludes: “With the imminent launch of NASA’s new space telescope, TESS, we hope to find even more of these rare and violent explosions.”