In the ultimate cosmic cataclysm, two ultra-dense bodies collide. For less than a second, incredible amounts of super-charged particles explode forth. These blasts could wipe out most life on Earth...and it's probably happened dozens of times already.
The main danger for Earth in these scenarios is that these particles - a mix of gamma rays, X-rays, and cosmic rays - could tear massive holes and deplete the ozone layer, leaving us unprotected from the steady stream of deadly cosmic radiation. These are rare occurrences, but not rare enough - new research from Washburn University suggests the ultra-violent explosions describe above could happen as often as every 100 million years, with devastating consequences for Earth.
It might seem paradoxical, but it's short bursts of cosmic radiation that we really have to worry about. These second-long bursts can only be created by the collisions of two neutron stars or two black holes - we're not sure which, but the effect is pretty much the same. The sheer amount of radiation unleashed in such a collision is on a whole different order of magnitude from the longer, relative tame bursts created in other types of cosmic explosions.
Astrophysicist Brian Thomas found that such bursts would be able to pretty much completely annihilate the ozone layer, leave land and marine life highly vulnerable to cosmic radiation. The long-term effects of that are difficult to comprehend. In all likelihood, we'd be looking at a whole new mass extinction event if such a burst hit us. And there's really nowhere to hide - if the explosion happens anywhere in the Milky Way, it could potentially hit our planet.
Of course, this is all just theoretical, and we can only estimate the frequency of these so-called short-hard radiation events from how often they occur in other galaxies. Our observations do suggest once every 100 million years is a good estimate, but it's possible they happen more or less frequently in our own galaxy, and it's still anyone's guess how many of the Milky Way bursts would actually hit Earth.
There's not much astronomy can tell us on that score - the constant movement of objects within our galaxy makes it very difficult to find evidence of past bursts - but we might be able to find evidence for past events right here on Earth. Thomas and other scientists believe the isotope iron-60 might be a sign of past bursts hitting Earth. If we can find huge build-ups of this isotope within the Earth's geological record, and if those layers of iron-60 line up with known mass extinction events...well, we might be able to understand just how devastating these bursts actually are.
Of course, those are a lot of ifs and perhaps a few too many leaps of logic. It also requires two different disciplines to come together to explore the problem, and Thomas admits that that isn't looking terribly likely right now:
"I work with some paleontologists and we try to look for correlations with extinctions, but they are skeptical. So if you go and give a talk to paleontologists, they are not quite into it. But to astrophysicists, it seems pretty plausible."