That now seems to be a pessimistic view because the latest evidence shows that GRBs focus their energy along two narrow beams, like a lighthouse might do on Earth, rather than exploding in all directions like a bomb. That does not mean that GRBs are not dangerous. Some theories suggest that anything caught in the beam, out to a distance of around light years, will be vaporised. Although none of the recently detected GRBs seem powerful enough, events in the distant past are another question.
While astronomers have yet to detect a really close GRB, they may already have picked up the most distant ones. This was the first piece of hard evidence that GRBs were linked to exploding stars, similar to supernovae. Now, XMM-Newton has captured another X-ray afterglow that shows similar features, strengthening the link. Ozone is also water soluble, which is particularly relevant to the Ordovician mass extinction as most life at the time was marine life.
A GRB would deplete the ozone layer in the upper atmosphere, allowing harmful UV radiation to reach the ground and thus have dire consequences for life. However, the ground-level ozone caused by the GRB would not be an additional hazard for life.
Understanding what causes mass extinctions is also important for the search for life in the Universe. Discovering a planet that ticks all the boxes for habitability may sound promising, but perhaps less so if a GRB or supernova recently occurred nearby.
In the hunt for life we also need to consider the possibility that any life that might have existed on a distant planet could already be extinct.
Written by Aaron Gronstal Source astrobio. Credit: NASA. So now German researchers have offered up another explanation: a massive explosion that took place within the Milky Way. One of the authors of the paper, Professor Ralph Neuhauser, from the Institute of Astrophysics at the University of Jena, said: "We looked in the spectra of short gamma-ray bursts to estimate whether this would be consistent with the production rate of carbon and beryllium that we observed - and [we found] that is fully consistent.
These enormous emissions of energy occur when black holes, neutron stars or white dwarfs collide - the galactic mergers take just seconds, but they send out a vast wave of radiation. Prof Neuhauser said: "Gamma-ray bursts are very, very explosive and energetic events, and so we considered from the energy what would be the distance given the energy observed.
Although the event sounds dramatic, our medieval ancestors might not have noticed much. If the gamma-ray burst happened at this distance, the radiation would have been absorbed by our atmosphere, only leaving a trace in the isotopes that eventually found their way into our trees and the ice. The researchers do not think it even emitted any visible light. Rare events. Observations of deep space suggest that gamma ray-bursts are rare.
They are thought to happen at the most every 10, years per galaxy, and at the least every million years per galaxy. Prof Neuhauser said it was unlikely Planet Earth would see another one soon, but if we did, this time it could make more of an impact. If a cosmic explosion happened at the same distance as the 8th Century event, it could knock out our satellites.
But if it occurred even closer - just a few hundred light-years away - it would destroy our ozone layer, with devastating effects for life on Earth.
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