A complete census of massive stars in our part of the Milky Way Galaxy has found an apparent link between the rate of core collapse supernovae and at least two of the last five mass extinctions here on Earth. Or so says a new paper appearing in the journal Monthly Notices of the Royal Astronomical Society.
A team led by Keele University in the U.K. used data from the European Space Agency’s Gaia satellite to characterize and map some 24,706 O- and B-spectral type stars out to distances of some 3200 light years. These stars are responsible for the sort of core collapse supernovae that can strip earthlike planets of their atmospheric ozone, create acid rain and leave their surfaces exposed to harmful ultraviolet radiation.
Two extinction events have been specifically linked to periods of intense glaciation, the authors note. Such glaciation could have been driven by dramatic reductions in the levels of atmospheric ozone due to a near-Earth core collapse supernovae. Thus, the team concluded that the late Devonian and late Ordovician extinction events, which respectively took place some 372 and 445 million years ago, were likely caused by such ancient supernovae.
Previous studies predated Gaia, and we were therefore able to derive a more accurate rate, Alexis Quintana, the paper’s lead author and a postdoctoral researcher in
astrophysics and astronomy at Spain’s University of Alicante, tells me via email. The "Near-Earth" rate we found was more consistent with the timescale of the historical mass extinction events, he says.
We calculated a near-Earth core collapse supernova rate that would result in approximately 2.5 supernovae over a billion year period, write the authors. This supports the view that nearby supernova explosions could have caused one or more of Earth’s recorded mass extinction events, they note.
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A Rough Ride
The Ordovician extinction killed 60 per cent of marine invertebrates at a time when life was largely confined to the sea, the Royal Astronomical Society notes. The late Devonian extinction was even worse, wiping out some 70 per cent of all Earth species, the RAS says.
How did the team make their calculations?
They first calculated the supernova rate within some 65 light years of our sun, then compared this rate with the approximate rate of mass extinction events here on Earth that have previously been attributed to nearby supernovae, the RAS says.
We estimated that supernova rates in the solar vicinity, or roughly 60 light years away, were consistent with a supernova explosion engendering one or more of the recorded mass extinction events on Earth, says Quintana.
What’s most surprising?
Our results reduced the supernova rate compared to previous work which used to be two to three times higher, Nick Wright, one of the paper’s co-authors and an astrophysicist at Keele University in the U.K., tells me via email. This obviously wasn’t consistent with the rate of mass extinctions on Earth, but our new estimate brings these numbers into better agreement which makes the link more likely, Wright tells me.
What's Next?
We intend to extend the census of O and B stars beyond this current limit, taking advantage of the exquisite precision of the Gaia data, says Quintana.
As for when the Milky Way can expect its next core collapse supernova?
One of the most well-known candidates is Betelgeuse, located in the Orion constellation (about 650 light-years away), says Quintana. While it is at a late stage of its life, it could still take up to 100,000 years to explode, he says.
The good news is that Earth is not currently in danger of an extinction level supernova.
There is no known massive star located close enough that a supernova explosion could be life threatening, says Quintana. And given the timescales we found doing this research, it’s safe to assume that such an event wouldn’t occur before millions of years, he says.