Astronomers witness death throes of a cocooned star

27 March 2018

An international team of astronomers including Dr Brad Tucker from The Australian National University (ANU) has seen the death throes of a star cocooned inside a dense shell of gas and dust, which ended in a violent explosion unlike a typical supernova.

“We’ve discovered yet another way that stars die and distribute material back into space,” said Dr Tucker from the ANU Research School of Astronomy and Astrophysics.

When the massive amount of energy from the blast slammed into the shell, most of the kinetic energy was immediately converted to light. It had a few near-death experiences before it ultimately died.

The final explosion of the star, which was about 1.3 billion light years away from Earth, lasted for only a few days – 10 times faster than a typical supernova.

Dr Tucker said learning about the life cycle of all stars, from birth to death, helped scientists better understand stars and their solar systems, and what that could mean for the potential of life on planets that go around them.

NASA’s Kepler Space Telescope – designed to hunt for planets across the galaxy – captured the rare event, called a Fast-Evolving Luminous Transient (FELT), which has bewildered astronomers for a decade because of its very brief duration.

Dr Tucker is one of the lead researchers of an international astronomy project that is using Kepler to find black holes, supernovae and other explosions in space.

Astronomers have discovered several FELTs with timescales and luminosities that are not easily explained by traditional supernova models.

Dr Tucker said FELTs appeared to be a new kind of supernova that gets a brief turbo boost in brightness from its surroundings.

He said Kepler’s ability to precisely sample sudden changes in starlight at a very fast rate allowed astronomers to quickly devise the new model for FELTs, and rule out alterative explanations.

This capability is needed for Kepler to discover planets outside of our solar system that briefly pass in front of their host stars, temporarily dimming starlight.

There have been a variety of theories to explain FELTs: the afterglow of a gamma-ray burst, a supernova boosted by a magnetar, which is a neutron star with a powerful magnetic field, or a failed Type Ia supernova.

“Using Kepler’s high-speed light-measuring capabilities, we’ve been able to see this exotic star explosion in incredible detail,” Dr Tucker said.

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

The new study is published in Nature Astronomy.

Lead author Dr Armin Rest, from the Space Telescope Science Institute in the United States, said astronomers using Kepler were now able to connect the models with the data.

“Kepler just makes all the difference here,” he said.

“When I first saw the Kepler data, and realised how short this transient is, my jaw dropped.”

Co-author PhD scholar David Khatami, from the University of California at Berkeley in the US, said this was the first time that scientists were able to 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 said.

As part of the study, the National Computational Infrastructure at ANU was used to process data from the SkyMapper telescope at ANU Siding Spring Observatory.