A tiny neutron star, which suddenly erupted releasing a huge amount of energy in a single burst most of it in X-rays and gamma rays just after Christmas, could have destroyed the atmosphere and eliminated life had the event occurred within ten light years of Earth.
The explosion that lit up the sky and fortunately was 50,000 light years away was the biggest bang in the Galaxy for 400 years. The burst that took place on December 27, 2004 was first seen by the orbiting X-ray observatory Swift, which later alerted other observatories around the world and followed what happened.
“If the explosion had occurred much closer to our solar system, say just 10 light years away, it would have severely damaged the atmosphere and possibly triggered a mass extinction of living things,” explained Researcher Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics.
“In other words, this was as much energy during that tenth of a second as all the other stars in the galaxy at that time, times over 1,000,” he said.
Britain's Royal Astronomical Society (RAS) said the flare, detected by satellites and telescopes operated by NASA and Europe, was so powerful that it bounced off the moon and lit up the earth's upper atmosphere. “For over a tenth of the second, it was actually brighter than a full Moon, and briefly overwhelmed delicate sensors,” RAS said.
Astronomers said the object that caused the flare was a magnetar - a tiny star made up of matter collapsed to a huge density, and possessing a powerful magnetic field. It is called (soft gamma repeater) SGR 1806-20 — a class of objects that periodically flare up and release bursts of gamma rays.
Magnetars, like other neutron stars, are the relics of larger stars that have consumed all their fuel and collapsed under the force of gravity, creating a supernova explosion that blows off the outer layers and compresses the core. So squeezed together is the matter that remains that a pinhead weighs as much as a battleship. If a neutron star created in this way is spinning, it also generates a huge magnetic field.
A magnetar has a surface crust of iron nuclei one kilometre thick, stressed by unbearable forces from its magnetic field. From time to time the crust deforms violently under these forces. The magnetic field generated by these objects, only a dozen or so of which are known, is about 1,000 trillion gauss, powerful enough to strip information from a credit card halfway to the Moon. The Earth’s magnetic field, for comparison, is a mere 0.5 gauss.
The event has now thrown up many questions, including the intriguing speculation that the dinosaurs may have been wiped out by a similar, closer gamma-ray explosion 65 million years ago, and not by climate change inflicted by an asteroid impact.
