29 May 2007

Gamma Ray Bursts And Climate--I Hope You Like Cold Weather

Gamma Ray Bursts(GRBs) occur with frightening regularity across the cosmos. Space scientists consider GRBs important enough to warrant an orbiting satellite observatory, SWIFT, to monitor the sources of GRBs.

SWIFT is responsible for several important discoveries about GRB sources, including this recent news item:
GRBs release in seconds the same amount of energy our Sun will emit over its expected 10 billion-year lifetime. The staggering energy of a long-duration GRB (lasting more than a few seconds) comes from the core of a massive star collapsing to form a black hole or neutron star. In current theory, inrushing gas forms a disk around the central object. Magnetic fields channel some of that material into two jets moving at near-light speed. Collisions between shells of ejected material within the jet trigger the actual GRB.

Early in the mission, Swift’s X-ray Telescope (XRT) discovered that the initial pulse of gamma-rays, known as prompt emission, is often followed minutes to hours later by short-lived but powerful X-ray flares. The flares suggested — but did not prove — that GRB central engines remain active long after the prompt emission.After analyzing GRB 060714, named for its detection date of July 14, 2006, Hans Krimm of Universities Space Research Association, Columbia, Md. and NASA’s Goddard Space Flight Center in Greenbelt, Md., and eight colleagues, have demonstrated that X-ray flares are indeed a continuation of the prompt emission, showing that GRB central engines are active much longer than previously thought.

Not so long ago, scientists began speculating that GRBs could have had a dramatic effect on Earth's history.
The idea that GRBs could have affected the course of evolution was first suggested two years ago (New Scientist print edition, 15 December 2001, p 10). John Scalo and Craig Wheeler of the University of Texas at Austin estimated that GRBs close enough to affect life in some way might occur once every five million years or so - around a thousand times since life began.

Now Melott believes he has palaeontological evidence that this actually happened at the end of the Ordovician period 443 million years ago, causing one of the five largest extinctions of the past 500 million years. Working with Bruce Lieberman, a specialist in fossil trilobites also at the University of Kansas, and other colleagues, he looked at the pattern of extinctions in the late Ordovician.

Now all of that is no doubt interesting in the context of Earth's biological past, but what might it mean to modern-day humans?
There are two bad things that happen if you get enough gamma rays smacking into you:

"1) They dissociate ozone molecules. Bad. Worse, they also zap nitrogen molecules, which then go out and zap ozone molecules. Either way, a lot of ozone goes away. It depends on how close the supernova or gamma-ray burst is, of course, but some studies have shown that a gamma-ray burst ... could eradicate 30 percent of ozone globally, with some local places dropping by more than 50 percent. In technical terms, that would suck.

"2) Those nitrogen atoms go on and make NO2 molecules, which is a reddish brown toxic substance. Not enough would be made, most likely, to hurt folks, but it's dark and absorbs sunlight, so they can contribute to global cooling. The Ordovician event may have been from a nearby supernova or gamma-ray burst, as there is evidence of increased UVB [ultraviolet light B] hitting phytoplanktons and also cooling at the same time.

"There is a third thing: cosmic rays, atomic nuclei accelerated to relativistic speeds, may also be sent our way by supernovae or gamma-ray bursts. No one is really sure. But there is a lot of evidence (and this shocked me) that the cosmic rays affect our weather by seeding clouds (I am unclear how this works in detail but I'll know better as I read more). More clouds means more cooling, so more cosmic rays could trip an ice age. Seriously.

A worldwide glacial epoch could easily be triggered by one of these events in our galactic neighborhood. There would be no warning to speak of.

We are lucky to have our warm, sunny days--long growing seasons for crops, plenty of time to soak up the gamma rays I mean sun's rays. For those who complain about a marginally warmer earth, may I suggest that you disconnect your air conditioners, and park your automobiles immediately. That would be most kind of you, for all of our sakes, and would partially excuse you for your lack of discrimination in your beliefs about the natural world. Thanks.

More on gamma ray bursts here, here, here and here.
Here are several abstracts of papers dealing with GRBs.

Hat tip Cocktail Party Physics

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