by Mark Aragona
If two nearby stars collide, it’s possible that we won’t be around long enough to appreciate it.
Scientists are finding evidence that radiation from massive cosmic events, such as star collisions, may have caused massive extinction events on Earth. Researchers believe that the incredible levels of gamma radiation emitted by these events may do long term damage to the ozone layer. However, they’re also discovering that even sudden short bursts of radiation have caused widespread extinction in our prehistoric past.
First detected in the 1960s by the Vela satellites, gamma ray bursts are the brightest known stellar events in the universe. Gamma rays are also the most powerful forms of radiation on the electromagnetic spectrum. There are two kinds: the long bursts, which are brighter, and the short-burst types which last less than a second but give off much higher amounts of radiation. Of the two, scientists say that the short-burst types prove to be a greater threat.
Short-burst types may be caused by the collision of cosmic bodies, like neutron stars or black holes. The gamma rays would radiate in a cone-shaped blast from the poles. If such a blast would occur nearby, that is, within our galaxy and pointing directly at the Earth, the results would be undeniably catastrophic.
Still, what are the chances of that happening? Currently, our satellites are detecting these bursts on average once a day. For a Milky Way-sized galaxy, they’re expected to occur once every 100,000-1M years, with only very few of them actually pointing straight at Earth. Since the Earth has been around for 4.5B years, it has been hit by quite a few of these gamma bursts, and they are likely to have caused several prehistoric species to become extinct. Based on fossil evidence, the Ordovician-Silurian extinction event, which happened 450 million years, was believed to have been caused by such a gamma ray burst that coincided with it.
As for the effects of such an event, consider the closest possible threats: the Wolf-Rayet stars, which may eventually turn supernova. Once they do and if Earth happens to be in the direct path of the gamma beams, it would deplete 25% of our ozone layer. This would then destroy several plant and animal species, disrupting food chains and causing mass starvation, not to mention exposure to radiation, which can kill outright or slowly through radiation poisoning.
It seems such events give more reason for humans to build space colonies within the next 100k years, so as to preserve the survival of our species.