On the threat of gamma ray bursts

Cecil, in his current article on cosmic threats to Life on Earth, mentions gamma ray bursts as one possible threat, but there’s one very important detail he left out. A nearby gamma ray burst will indeed fry everything it hits, but there’s no way one could wipe out all life on Earth, or even all humans. Unlike a conventional supernova, which can last for months at near-peak brightness, the interesting (read: deadly) portion of a gamma-ray burst is over in mere seconds. And while gamma rays are highly penetrating, they’re still not going to make it through an entire planet. So if we ever get hit by a GRB, it’s going to flash-broil one hemisphere of the planet, but the other half will be untouched.

Initially, at least. One of the effects of a gamma-ray burst is anticipated to be conversion of much of the atmosphere into various nitrogen-oxygen compounds. Some of those are opaque, and they could persist in the atmosphere for years before breaking back down. During that time, they’d spread across the planet, including the initially-spared hemisphere, shrouding everything in darkness. This is something humans, with our ability to store and preserve food, could survive, but it wouldn’t be fun, and many more would die.

Plus, of course, the effects of an entire hemisphere’s worth of now-dead plants and animals. It’s anyone’s guess what that would result in, especially since most of the organisms that would decompose them will also be dead, but I’m sure that it wouldn’t be gentle on the surviving ecosystems.

Would these new compounds be lighter than air, such that they would stay high in the atmosphere? Or if they mixed with the air close to the ground, wouldn’t the air become toxic?

Glad to hear I’ve a 50/50 chance to survive the initial GRB, better odds than Vegas …

What about life in water? Doesn’t water have a certain amount of shielding effect from gamma radiation?

Are there any known candidates locally?

For the half that gets flash-broiled in mere seconds, at least it sounds like it would be relatively fast and merciful (just like the end, for most of humanity, in Cat’s Cradle, who got flash-frozen). It’s probably the best we can hope for.

Would the radiation persist in canned food? Soil?

If the radiation decomposes within a month or so, the dead hemisphere (assuming there is food stored in large quantity) would be the place to migrate should a blackout occur and destroy crops.

Something like the scene in Terminator 2, just on a hemispheric scale perhaps?

Phil Plait, who posted here as The Bad Astronomer, walked through various world ending scenarios in Death from the Skies!. A recommended entry point into Astronomy.

Would a GRB literally broil us by raising the thermal temperature to some high degree? Or are all mentions of “cooking” (by whatever synonym) just metaphors for radiation poisoning?

Would we all literally get cooked, or just radiation poisoned?

Would inanimate things made of wood, plastic, metal, etc., get melted, or incinerated? Would canned goods on the shelves in all the markets explode? Would raw meat in all the supermarkets get cooked? Or incinerated to a cinder? Would all the gasoline in just-barely-underground tanks at all the gas stations explode in flame? Would all the smaller bodies of water get completely boiled off? Would vast quantities of sea water get evaporated, unleashing the proverbial rainstorm of 40 days and 40 nights (if not 40 years)? Would the entire exposed half of the earth turn into a tropical rain forest for the next 10000 years?

If any of the above is true, then the ecological effects would certainly spread around the entire globe, and not be limited just to the exposed side.

I think the effect gamma rays have on water is that it will disassociate the molecule, splitting it into H[sup]+[/sup] and OH[sup]-[/sup] ions. However at higher levels even the OH[sup]-[/sup] ions will disassociate into more H[sup]+[/sup] and O[sup]-2[/sup] ions. As these ions recombine, some will become H[sub]2[/sub] and O[sub]2[/sub] molecules, as well as water (H[sub]2[/sub]O) and peroxide (H[sub]2[/sub]O[sub]2[/sub]). H[sub]2[/sub] and O[sub]2[/sub] as gases would quickly rip apart most all living cells.

Biochemicals would fair no better …

Dr. Phil Plait (an esteemed former Doper), in his book “Death from the Skies! The Science behind the End of the World” says the following about gamma ray bursts:

Plait goes on to describe the situation if Eta Carinae (7500 ly away) went hypernova and the resultant GRB was aimed at us.

It could be as bright or even 10x brighter than a full moon for a few seconds or minutes. People would get sunburned by the UV light.

There would be a huge EMP pulse that would wipe out most electronics. The ozone layer would be reduced by about 35% globally as a result of the gamma rays. This would screw up the microorganisms at the bottom of the food chain good, possibly calling an extinction-level event. A huge amount of reddish-brown nitrogen dioxide also created in the atmosphere as a result of the GRB’s action on the ozone layer would reduce sunlight by a significant amount, causing global cooling enough to trigger an ice age, and enough nitric acid would be produced from that nitrogen dioxide to cause severe acid rain.

Finally, there would be something on the order of 300 billion muons per square inch hitting the Earth on the side facing the blast, which is 10x the lethal dose, and would penetrate up to half a mile into rock, and a full mile into water.

Does all that radiation, muons, and whatever else is in a GRB travel at literally the speed of light?

More to the point: If a GRB is headed our way, would we be able to see it coming before it gets here?

Gamma rays travel at the speed of light, because they are light. Neutrinos travel at so close to the speed of light that the difference is usually negligible, but they’re harmless. Anything else we’d get dosed with (including the muons) is significantly slower than light, but it doesn’t matter, since they’d be produced in the upper atmosphere from the gamma rays hitting it, not directly by the supernova. The only way we could “see one coming” would be to recognize what a star looks like just before it goes burst, and we don’t know that.

And radiation never “sticks around”, at all. What can happen is that radiation can transmute atoms that it hits into other, unstable atoms which later decay, but that’s only a significant issue for neutron radiation, which doesn’t last long enough to reach Earth from any astronomical source.

nm Chronos answered my question

I see Cecil refers to question-writer Travis van Dreven as “Trevor” at the end of the column. Can he blame this on gamma rays?

Yeah, but with some seven billion of us on the planet, it’s sounding pretty likely that at least a few of us will die from either a supernova or a gamma ray burst.

Definitely a headline there.

I’ve probably been whooshed, but just in case - your comment would only make sense if the chance of one person getting fried is independent of anyone else getting fried. Since that is not the case (as Tom Lehrer put it so succintly “We will all go together when we go”) the fact that there is a 1 in 14 million chance of getting fried does not imply that it is very likely that one of the 7 billion of us will get fried.

To elaborate on this, bump’s quote of Dr. Phil Plait included, “Assuming the event would cause a mass extinction, killing everyone on Earth, the odds of your specifically dying from one over your lifetime are therefore about 1 in 10 million.” All whooshing aside, does the earth’s population factor into the probability of 1 in 10 million (or 14 million)? Since it is an all-or-nothing deal, isn’t the relevant statistic the probability of earth being fried in any one life-span (~75 years), regardless of population?

I’d expect that the dead half of the biosphere would be turned into carbon dioxide pretty quickly; the plants would cease to transpire and dry out, catching fire, and probably a few surviving microorganisms (and spores drifting in from the surviving side) will degrade the rest.
The planet would have a NOX winter followed by a CO2 summer, and none of this would be good.

It’s thought that one of the mass extinctions we’ve already had was caused by a gamma ray burst. I discovered that a while ago when I was writing about them. Also discovered that gamma ray bursts are rare in this galaxy. I’ve got both source references linked in what I wrote. So scroll down to the Gamma-ray burst entry if you want the links to the original source. Or take my word for both of those statements. Up to you.