Scientists have obtained the first view of the initial burst of light from the explosion of a massive star, thanks to lucky snapshots taken by an amateur astronomer in Argentina. While testing a new camera, Victor Buso captured images of a distant galaxy before and after the supernova’s ‘shock breakout’ – when a supersonic pressure wave from the exploding core of the star hits and heats gas at the star’s surface to a very high temperature, causing it to emit light and rapidly brighten.
To date, no one has been able to capture the ‘first optical light’ from a supernova, since stars explode seemingly at random in the sky, and the light from shock breakout is fleeting. The new data provide important clues to the physical structure of the star just before its catastrophic demise and to the nature of the explosion itself. “Professional astronomers have long been searching for such an event,” said Alex Filippenko, an astronomer at University of California, Berkeley in the US.
“Observations of stars in the first moments they begin exploding provide information that cannot be directly obtained in any other way,” said Filippenko, who followed up the discovery with observations that proved critical to a detailed analysis of explosion, called SN 2016gkg. On September 20, 2016, Buso was testing a new camera on his 16-inch telescope by taking a series of short-exposure photographs of the spiral galaxy NGC 613, which is about 80 million light years from Earth and located within the southern constellation Sculptor.
Luckily, he examined these images immediately and noticed a faint point of light quickly brightening near the end of a spiral arm that was not visible in his first set of images. Astronomer Melina Bersten and her colleagues at the Instituto de Astrofisica de La Plata in Argentina soon learned of the serendipitous discovery and realised that Buso had caught a rare event, part of the first hour after light emerges from a massive exploding star. She estimated Buso’s chances of such a discovery, his first supernova, at one in 10 million or perhaps even as low as one in 100 million.
“It’s like winning the cosmic lottery,” said Filippenko. Bersten immediately contacted an international group of astronomers to help conduct additional frequent observations of SN 2016gkg over the next two months, revealing more about the type of star that exploded and the nature of the explosion. Researchers estimated that the initial mass of the star was about 20 times the mass of our Sun, though it lost most of its mass, probably to a companion star, and slimmed down to about 5 solar masses prior to exploding.