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Sea Life Wiped Out by Neutron Star Collision?
Memorize writes "Scientists report in the Journal of Astrophysical Letters that a mass extinction of marine life 450 million years ago might have been caused by radiation from an exploding star, such as a collision between two neutron stars, or a neutron star collapsing into a black hole. Such an event would cause a ten-second burst of gamma radiation, and if it occurred within our galaxy, it could have wiped out many species on earth. At least if astronomers find out that an asteroid is heading our way, we can do something about it, but if there is a gamma burst, we get no warning. And if we did, would there be any way to protect the planet?"
Gamma ray bursts are an area of active research; we now believe that they emit radiation along some polar axis, rather than isotropically in every direction. That probably accounts for the difference in distances you've seen quoted; for some fixed power level, an anisotropic GRB is dangerous from a greater distance if you happen to lie in the beam.
Given a number of confused responses to this, let's just remind everybody: it's not the gamma rays that kill (they would only get half of the globe anyway), it's the stripping away of the ozone layer followed by intense UV radiation. That's why it's a global effect.
While that would cause huge famines and disease and kill almost all humans, it is something that our species could survive given our technology.
If the 6,000 LY limit is justifiable, I don't think it's quite as bad as you make out... at least not without some much more definitive research.
6,000 Light Years is practically next door on the galactic scale. It's certainly not infeasible (for someone qualified) to simply look at a survey of what's in our local space and determine immediately if we're at risk based on anything that looks unstable. (I'm not a professional astronomer, so someone's welcome to correct me if they know otherwise.)
The most obvious potential threat that's relatively close is probably Eta Carinae, which is about as massive as it's possible to get, and it's been hypothesised in the past that there's a small chance we might be at risk from a sudden gamma ray burst from it. But it's still about 8,000 light years away and there's still not enough known about it to have any accurate idea of when it's going to blow itself apart, either tommorrow or millions of years from now.
If there's still a reasonable chance that it could happen at some point in the future, this doesn't mean that there's any chance at all of it happening tommorrow. Stars orbit move a lot relative to each other sa they orbit the galactic centre. Our Sun does that in about 226 million years, but in the space of hundreds of thousands of years, galactic material barely moves relative to each other at all. It's feasible that at some time in the next few million years or more we will be close to something dangerous for some period of time. If we're not close enough to it now, though, the chance of that happening is still zero.
This is all dependent on that 6,000 Light Year limit being correct, of course. Clearly it's still all subject to change as we learn more about the Universe, which we still know next-to-nothing about. I don't think there's much point worrying about the great unknown, though, at least until we know enough to know that there's actually a risk. Otherwise it would just lead to paranoia.
Any gamma burst from a single point will only fall on half the Earth's surface directly. What stops us from just hopping across to the other half, instead of needing scifi tech to survive?
Short Answer: RTFA
Long Answer:
The Gamma rays would destroy the ozone on the unlucky side. Once the ozone redistbutes, you are down to 50% everywhere. That is, aparently, enough to kill plankton. Probably would kill land plants, too.
So, on the unlucky side everybody dies. On the lucky side, crops fail for several years. Very bad news, though I doubt it would actually exterminate the human race. Plants would still grow in UV filtered green houses.
A pre-print of the research article is available. The impression that I get is that they don't claim to really "prove" the idea, but rather pose it as a very interesting hypothesis which is compatible with the evidence and deserves further investigation. In particular, I think their claim is that gamma ray bursts can explain the evidence of rapid cooling from the extinction period. Of course, the popular press claims this tentative hypothesis like it was already a concrete fact, but that's what the press does.
Here's the basic info:
Title: Did a gamma-ray burst initiate the late Ordovician mass extinction?
Abstract: Gamma-ray bursts (hereafter GRB) produce a flux of radiation detectable across the observable Universe, and at least some of them are associated with galaxies. A GRB within our own Ggalaxy could do considerable damage to the Earth's biosphere; rate estimates suggest that a dangerously near GRB should occur on average two or more times per billion years. At least five times in the history of life, the Earth experienced mass extinctions that eliminated a large percentage of the biota. Many possible causes have been documented, and GRB may also have contributed. The late Ordovician mass extinction approximately 440 million years ago may be at least partly the result of a GRB. A special feature of GRB in terms of terrestrial effects is a nearly impulsive energy input of order 10 s. Due to expected severe depletion of the ozone layer, intense solar ultraviolet radiation would result from a nearby GRB, and some of the patterns of extinction and survivorship at this time may be attributable to elevated levels of UV radiation reaching the Earth. In addition a GRB could trigger the global cooling which occurs at the end of the Ordovician period that follows an interval of relatively warm climate. Intense rapid cooling and glaciation at that time, previously identified as the probable cause of this mass extinction, may have resulted from a GRB.