How to kill a star? Astronomers see a 'demolition derby' scenario

New research shows gamma-ray burst may have been caused by a collision of two compact stars

An artist's impression shows an immensely energetic explosion called a gamma-ray burst. Reuters

Astronomers have spotted an immensely energetic explosion emanating from an ancient galaxy, apparently triggered by a type of star destruction hypothesised for decades but never before observed.

You might call it stellar death by demolition derby.

Researchers said the gamma-ray burst they observed may have been caused by the collision of two compact stars in the densely packed and chaotic environment near a supermassive black hole at the centre of this elliptically shaped galaxy.

The Milky Way galaxy stretches across the sky above the landscape of the Chilean Andes near the La Silla Observatory. Photo: Babak Tafreshi

They suspect the two doomed stars were neutron stars, which pack roughly the mass of our Sun into a sphere only the size of a city.

“In order to explain the gamma-ray burst, it has to have been a compact star, so not one like the sun,” said astronomer Andrew Levan of Radboud University in the Netherlands, lead author of the research published this week in the journal Nature Astronomy.

Wen-fai Fong of Northwestern University in Illinois, astrophysicist and study co-author, said: “Gamma-ray bursts are the most powerful explosions in the universe. They release more energy per unit time than any other known cosmic phenomena.

“So they are really superlative in their properties. Their name comes from the first type of light that we see, gamma-rays, but they actually emit across the electromagnetic spectrum.”

Immense gravitational forces exerted by the black hole at the galactic centre may wreak havoc, perturbing the motion of nearby stars and other objects and increasing the chances of collisions – akin, the researchers said, to a demolition derby.

“Most stars in the universe die in a predictable way, which is just based on their mass,” Mr Levan said. “This research shows a new route to stellar destruction.”

Very massive stars – more than 10 times the Sun's mass – die in a supernova blast that leaves behind neutron stars or even denser black holes, whose gravitational pull is so strong no matter or light can escape.

Relatively low-mass stars like our Sun puff up and blow off their outer layers, transforming into a stellar remnant called a white dwarf.

The new findings show another path to stellar demise.

“The idea that stars also can die through collisions in extremely dense regions has been around since at least the 1980s. So we've been waiting for 40 years for the signatures to be found observationally,” Mr Levan said.

The researchers used data from orbiting and ground-based telescopes to study the gamma-ray burst in a galaxy about 3 billion light-years away from Earth, roughly in the direction of the constellation Aquarius.

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