Serendipity: Galactic catastrophes

IN THE LATE Sixties, America launched the Vela satellites, designed to monitor the Limited Nuclear Test Ban Treaty by detecting gamma rays given off during nuclear blasts. The Americans could already monitor nuclear tests in the atmosphere and below ground, and now they were able to see if the Soviets were conducting clandestine nuclear tests in space. In 1967, a Vela satellite detected a blast of gamma radiation, and the American military immediately panicked.

Fortunately, it turned out that this was nothing to do with the Soviets, but rather was the result of a cosmic event. The Vela satellites have detected several other gamma ray bursts (GRBs), lasting from a fraction of a second to a few seconds. Over the last decade, astrophysicists have been able to pinpoint their location, and it is clear that the mysterious objects that cause GRBs are usually at the edge of the observable universe, and therefore the energy created must be enormous, because the radiation is still fantastically bright by the time it reaches us. GRBs are typically billions of times brighter than a supernova and they represent a power output equivalent to millions of galaxies.

Some suggest that GRBs are the result of a cataclysmic collision between two neutron stars, others hypothesise that we are observing the consequences of a neutron star falling into a black hole. While astrophysicists are both bemused and awe-struck by the most brilliant flashes in the cosmos, scientists searching for extraterrestrial intelligence view them as a possible reason why we have not yet been visited by aliens.

James Annis, a physicist at Chicago's Fermi National Laboratory, has recently pointed out that a GRB that occurs in a particular galaxy is likely to irradiate and kill all life within that galaxy. Furthermore, a galaxy is likely to have a GRB every few hundred million years, and so it seems that galaxies are sterilised at regular intervals. In a paper published in the Journal of the British Interplanetary Society, Annis suggests that GRBs might destroy civilisations before they have been around long enough to develop the technology required for galactic travel.

On the other hand, astronomer Paul Davies is a little less pesimistc. A gamma-ray burst might kill land-based creatures, but deep sea creatures would probably survive, shielded by the water above them. Furthermore, organisms on the far-side of the planet, the side facing away from the radiation, would also be safe, protected by the mass of the planet between them and the GRB. In reply, Annis points out that a GRB would destroy the ozone layer and therefore have a global impact. Either way, it is unlikely that there will be a GRB in our galaxy in the next 10 million years, and so there is probably nothing for us to worry about for the time being.