A shockwave blasted from a giant exploding star has been spotted in visible light for the first time.
The Kepler space telescope saw the red supergiant, more than 270 times the radius of the Sun and 750 million light-years away, collapse on itself and blast a brilliant flash – what astronomers call the "shock breakout".
"It's like the shockwave from a nuclear bomb, only much bigger, and no one gets hurt," said Brad Tucker, an astronomer from the Australian National University, who was involved in the study.
The work, available online at arXiv and accepted for publication in The Astrophysical Journal, will help astronomers understand how these complex explosions create many of the elements that make up solar systems, including our own.
Stars die when they run out of fuel. And if they're big enough, their core collapses to form a super-dense neutron star. Energy rebounds off the core in the form of a shockwave travelling at 30,000 to 40,000 kilometres per second.
The shockwave also prompts nuclear fusion, creating heavy elements such as gold, silver and uranium.
But while plenty of supernova explosions have been seen – after all, they shine so brightly it's easy to spot them in distant galaxies – their early stages have escaped observation.
For a typical supergiant, the researchers write, the shockwave can traverse the distance from core to the fluffy outer layers of the star in an hour.
But with Kepler keeping tabs on 500 stars every 30 minutes in visible light, Tucker and colleagues from the US were able to capture that initial shockwave emitted from a red supergiant.
A second star, which at 460 times the radius of the Sun was even bigger than the first, also exploded, but its shockwave escaped detection. Tucker thinks this is because the star was so big that the shockwave didn't make it all the way out.