The first moments of a dying star

Saturday, 1 December 2018

The white dwarf (right) stripping the material from its neighbouring star. When it takes too much, it finally collapses and explodes under its own weight, releasing a supernova.

It was one of the largest explosions in the universe.

On the right of this digital artist's impression, you can see a white dwarf. This small, ancient star has captured a large young star in its gravity, and is leaching its fuel.

But the dwarf sucks too much, gathering so much fuel that it explodes under its own weight. This explosion is known as a supernova, and is one of the most powerful events in the universe.

The explosion happened in another galaxy about 170 million light-years away; in February the light finally reached Earth after travelling for 170 million years.

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Luckily, we had telescopes in place to spot it. Nasa's Kepler space telescope detected it.

The space agency retired the Kepler space telescope in October, following the exhaustion of fuel supplies after nine-and-a-half years of ground-breaking operations.

However, Nasa said on its website: 'From December to May, while there was still fuel left, the Kepler team oriented the spacecraft toward two distinct patches of sky that were simultaneously observable from Earth by ground-based observatories. The telescopes were able to view both patches of sky teeming with galaxies. Each of these thousands of galaxies has billions of stars.'

From Earth, the explosion shone a brilliant blue, an indication the supernova reached billions of degrees in temperature.

'It is,' said Dr Brad Tucker, 'a very, very massive event'.

Tucker, an astronomer at the Australian National University, was part of a team of 130 international scientists who have spent months studying data and images from the star's explosion, captured by telescopes around the world.

Supernovas, among the most powerful explosions in the galaxy, are exceedingly rare. Astronomers knew they could be caused when two white dwarfs – ancient superheavy stars that have run out of fuel and been compressed by gravity to about the size of our planet – slammed into each other.

But they suspected there was another trigger. A single white dwarf might prey on another, younger star, sucking its material away. At some point, the white dwarf might gain so much mass it became unable to support itself.

And then, it was theorised, it would explode.

This white dwarf's fate seemed to confirm that theory, Tucker said.

Like a nuclear bomb, the supernova produced a huge shockwave that raced through space ahead of the explosion itself.

Through their telescopes, the astronomers spotted that shockwave hit the white dwarf's neighbouring star. The shockwave was strong enough to 'shove it out of the way,' says Tucker.

'It won't cause the other star to blow up, but it will mess it up.'

Scientists will use the recording of the star's death to study how supernovas form and ignite. There are many unanswered questions, says Tucker.

The find is published on Saturday in The Astrophysical Journal Letters and The Astrophysical Journal.