Extract from ABC News
Around a billion years ago, a massive yellow star exploded in the constellation of Cancer.
If the Kepler space telescope hadn't been looking in the right place at the right time a billion years later, we'd never know about it.
Key points:
- Astronomers have detected the earliest part of a shock wave as it triggered a supernova explosion
- The discovery helps fill in the gaps about what happens during the entire process of an explosion
- The information can help astronomers understand how different types of stars live and die
But in 2017, the now-defunct telescope captured the event from beginning to end in unprecedented detail.
The discovery of the event by a team of international astronomers trawling through Kepler data appears online ahead of publishing in the Monthly Notices of the Royal Astronomical Society.
"We've always missed the very, very start of a [supernova] because it is so exceedingly difficult to capture that," said lead author Patrick Armstrong, a PhD candidate at the Australian National University (ANU).
As a massive star reaches the end of its life, it burns up all its fuel.
It gets very bright, then it dims as it puffs up and starts to collapse, sending out a shock wave that triggers a cataclysmic explosion.
The initial brightening phase had been captured before by Kepler in 2016.
But this is the first time the entire shock wave during the dimming phase in the lead-up to the explosion has been captured in detail, Mr Armstrong said.
"Stars will live for millions and millions of years.
"They will explode in a matter of weeks and the shock cooling curve only lasts a matter of days.
"So over their millions of years of lifetime, we really have to capture a few days."
The international team saw the distinctive rise and fall of the event occur over a three-day period in the data captured by Kepler.
Right place, right time
The Kepler space telescope, which was retired in 2018, was designed to stare at slabs of the sky to search for distant planets.
But because it spent up to 40 days taking photo after photo of the same patch of sky before moving to the next patch, it was perfect for finding objects that suddenly appeared – and disappeared – in a flash.
"During one of these times we were just lucky and a supernova happened to explode while we were staring at that point in the sky, and we were able to get this really amazing piece of data," Mr Armstrong said.
And it is "absolutely stunning" data, says Joss Bland-Hawthorn, an astronomer at the University of Sydney who was not involved in the research.
While other telescopes provide a smattering of data points scattered across the rise and fall of an explosion, the data from this discovery is a solid line that weaves its way from beginning to end.
Professor Bland-Hawthorn says the difference between this discovery and previous data is like seeing an explosion as a real-time movie versus a series of stills with gaps in between.
"What [Kepler] has done is give you 100 times more measurements," Professor Bland-Hawthorn said.
"You see it from the beginning, through the explosion and when it cools down after the explosion."
The secret life of stars
Professor Bland-Hawthorn says the beauty of this detail is that it helps us learn about the evolution of massive stars.
"These stars live fast and die young.
"And they are very important because ... up to half [the elements in the natural world] came from these sorts of explosions."
Study co-author Brad Tucker from ANU says the discovery can give astronomers a better picture of how different types of stars collapse.
The star that created this supernova was likely to be a yellow super giant 100 times the size and about 17 times the mass of our Sun.
"What we are trying to do is to connect what this star looks like during its life and how it ends," Dr Tucker said.
"It's ultimately that complete picture that will tell us when they explode, what energies they produce and what [elements] they produce."
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