Exploding stars known as supernovas may have sparked mass extinctions that wiped out up to 85% of animals on Earth.
‘Supernova explosions are some of the most energetic explosions in the Universe’, said Dr Nick Wright, an astrophysics lecturer at Keels University.
‘If a massive star were to explode as a supernova close to the Earth, the results would be devastating for life on Earth.’
That’s not just a future possibility – it ‘may have already happened’, a new study published in the Monthly Notices of the Royal Astronomical Society journal suggests.
Dr Wright was part of a research team, led by Dr Alexis Quintana, who conducted a ‘census’ of supernovas within our galaxy – the Milky Way.
When it comes to ‘going out with a bang’, no one does it better than stars.
Massive, dying stars – five to 10 times the size of our Sun – start to collapse when they run out of fuel.
It happens with such abrupt force, it sends out powerful shockwaves and an expanding cloud of hot gas.
If they’re big enough, those supernovas leave a black hole in their wake.
They are, hands down, the biggest explosions humans have ever witnessed. But we have only ever done so from afar.
Supernovas included in Quintana and Wright’s census were up to 3,260 light-years away from the Sun. For reference, one light-year is 9.5 trillion kilometres.
What they were looking for was the rate at which these massive stars form in the Milky Way, and within close proximity (well, 65 light-years, if you can call that close), to Earth.
They wondered whether this lined up at all with mass extinction events on Earth, some of which have previously been blamed on nearby supernovas.
Among these are the late Devonian extinction, 372 million years ago, and the late Ordovician extinctions, around 445 million years ago.
Somewhere up to 75% or 85% of animal species, mostly marine, were annihilated in those extinction events.
Among those were the huge, predatory fish, Dunkleosteus – pronounced like uncle – with armoured eyeballs and no teeth, just jaws it filed sharp each time it opened its mouth.
It is possible that a supernova could have stripped the Earth’s atmosphere of its ozone – even more so than the greenhouse gases trapped inside – and exposed the planet’s life to often fatal levels of ultraviolet radiation.
Such damage to Earth and its ozone could last for 100,000 years, with its effects felt long after, stifling attempts by doomed species to survive.
This latest study supports that theory. Dr Alexis Quintana, now with the University of Alicante, said: ‘It is a great illustration for how massive stars can act as both creators and destructors of life.
‘Supernova explosions bring heavy chemical elements into the interstellar medium, which are then used to form new stars and planets.
‘But if a planet, including the Earth, is located too close from this kind of events, this can have devastating effects.’
They’re not the first to suggest that the violent death of a star nearly wiped out life on Earth.
Researchers at the University of Illinois, Urbana-Champaign, blamed ‘killer cosmic rays from nearby supernovae’ for the Devonian extinction, in a study published in the Proceedings of the National Academy of Sciences in 2020.
‘Earth-based catastrophes such as large-scale volcanism and global warming can destroy the ozone layer too’, astronomy and physics professor Brian Fields, who led the study, said.
‘But evidence for those is inconclusive for the time interval in question.
‘Instead, we propose that one or more supernova explosions, about 65 light-years away from Earth, could have been responsible for the protracted loss of ozone.’
Co-author Adrienne Ertel, a graduate student at the time, said: ‘To put this into perspective, one of the closest supernova threats today is from the star Betelgeuse, which is over 600 light-years away and well outside of the kill distance of 25 light-years.’
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