When Victor Buso was photographing the night sky in September 2016, he had a one in 10 million chance that he’d capture a supernova. The universe made sure he took it.
When a heavy star burns out with a giant explosion, it’s a supernova. Astronomers have observed supernovae but haven’t caught many of them in the moment of their birth itself. More specifically, we don’t have any records of the first few hours of a type IIb supernova explosion – where the progenitor star first loses a large part of its outer layers before blowing up.
Fortune amended this gap in 2016.
On a calm and clear night in September that year, Victor Buso, an amateur astronomer and astrophotographer, was testing a camera he had mounted on his telescope in Rosario, Argentina. He pointed his setup at NGC 613, a spiral galaxy over 65 million lightyears away, and took a series of pictures. Each short had 20 seconds of exposure over 90 minutes, from 1:30 am to 3 am local time. Buso didn’t realise what he’d managed to get on camera until later: the first ever visible-light images of a supernova shockwave.
The first 20 minutes of Buso’s observations show a quiet sky to the galaxy’s south. After 45 minutes – and some 40 photos into Buso’s sequence – a supernova erupts into life. It can be seen getting bigger and brighter as the sequence continues, with maximum brightness nearly tripling in the last few pictures. This is the first time a supernova has been photographed in such quick succession.
In the middle of his shoot, Buso had noticed that a new spot of light had appeared in his pictures that kept getting brighter. He realised he could be looking at a developing event and attempted to contact the Astronomical Observatory of Córdoba.
When that didn’t work – possibly because it was the middle of the night – he called Sebastián Otero of the American Association of Variable Star Observers. The two put out an announcement soon. Otero also reported the bright spot to the Transient Name Server, the official body for reporting temporary events, or transients, with short lifespans. Soon after, the All Sky Automated Survey for SuperNovae, an automated program with 20 telescopes around the world searching for supernovae, and the Asteroid Terrestrial-impact Last Alert System telescope, Hawaii, looking for moving objects in the sky, confirmed the event for what it was: a type IIb supernova.
It was designated SN 2016gkg. The detection was announced immediately and a large-scale monitoring effort began the next day, September 21, 2016. It was observed in the visible, X-ray and ultraviolet parts of the spectrum, and quickly became one of the most-studied supernovae in history.
The wave of death
Buso’s photos contained a particularly unique gem, an astrophysics Arkenstone, if you will: the signs of a shock breakout. In the last few moments of their lives, stars weighing 10x the Sun collapse under their own weight. This happens because the star has run out of lighter elements to fuse and starts trying to fuse iron. However, unlike lighter elements, iron fusion consumes more energy than it produces, forcing the star to eat itself.
The result is a shockwave from the core that ripples out through the star’s body, heating everything up by millions of degrees, eventually reaching the surface in a blinding flash of energy. “The shock breakout phase is like the first flash of light from when you light a matchstick,” Parshati Patel, an education and outreach coordinator at the Centre for Planetary Science and Exploration, Western University, Canada, told The Wire. “It is a wave of death starting from the core and reaching the surface.”
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Astronomers have expected shock breakouts to occur because their theories and computer models predicted it – but they weren’t observed until recently. In 2008, Kevin Schawinksi of the University of Oxford and his team observed the shockwave’s precursor (a UV emission) followed by the shockwave itself shooting through SNLS-04D2dc, a supernova about 2.5 billion lightyears away.
In 2016, the Kepler space telescope caught the first shock breakout of a type II supernova in visible light. Buso’s pictures are the second such set of recordings, and the first of a type IIb supernova. “What is new here is that we have seen the explosion within a few hours of it occurring, meaning we have been able to watch the shock breakout as it happens,” said Alan Duffy, an astrophysicist and associate professor at Swinburne University, Australia.