A few months ago, Australian researchers uncovered evidence of nearby supernovae that happened in the last 8 million years, and now an international team has been able to model the impact of these explosions on Earth’s living organisms.
The research, soon to be published in The Astrophysical Journal Letters and available online, indicates that the biology on our planet was exposed to 20 times more cosmic rays than usual, and the supernovae might have even had a lasting effect on our planet climate.
“I was surprised to see as much effect as there was,” said co-author Adrian Melott, professor of physics at the University of Kansas, in a statement. “I was expecting there to be very little effect at all. The supernovae were pretty far way – more than 300 light-years – that’s really not very close.”
When a massive star reaches the end of its life, it will begin to collapse on itself. The process is so quick and it liberates so much energy that the star is blown apart, creating heavy elements and shooting them across space.
Suddenly the star will appear millions of times brighter, irradiating the surrounding universe with photons and cosmic rays. Using computer simulations, the team was able to quantify how much light and charged particles (which make up the cosmic rays) arrived on Earth.
“The big thing turns out to be the cosmic rays,” said Melott. “The really high-energy ones are pretty rare. They get increased by quite a lot here – for a few hundred to thousands of years, by a factor of a few hundred.
“The high-energy cosmic rays are the ones that can penetrate the atmosphere. They tear up molecules, they can rip electrons off atoms, and that goes on right down to the ground level. Normally that happens only at high altitude.”
The researchers actually suggested a potential link to a small mass extinction event that happened 2.59 million years ago. In large quantities, cosmic rays might have been able to disrupt enough of the ozone to affect Earth’s atmosphere
“There was climate change around this time,” added Melott. “Africa dried out and a lot of the forest turned into savannah. Around this time and afterwards, we started having glaciations – ice ages – over and over again, and it’s not clear why that started to happen.
“It’s controversial, but maybe cosmic rays had something to do with it.”
While the research is interesting, it is not conclusive. The team is hoping that the analysis of fossils from that epoch will show a distinct astrophysical signature.