Thursday, December 31, 2009

A blast from the past

This story presented the best opportunity for ending the year with a bang -- Phil Plait's Bad Astronomy blog reminds us of the story that was lost five years ago in the wreckage of human lives and property damage that occurred when a massive tsunami struck the eastern Indian Ocean on December 26, 2004. The story from a day and a half later, on December 27, 2004, got much less coverage. A massive burst of energy was observed from a magnetar, a type of neutron star. The blast was powerful enough to knock out satellites, and had it been closer, it would have potentially been an extinction level event.

The magnetar in question was SGR 1806-20, now believed to be the most powerful magnetic object known -- strength of 10E15 gauss (compared with between 1 to 5 gauss on our own Sun). 10E15 is the number 1 followed by 15 zeroes. To put this in context, a fridge magnet has a field strength of about 100 gauss, while more exotic neodymium-based magnets can be 10 to 20 times more powerful, up to 2,000 gauss. A medical NMR (Nuclear Magnetic Resonance) imaging device will generate magnetic fields from 10,000 up to 30,000 gauss. The field surrounding this particular magnetar is a hundred billion times more powerful than the NMR machine.

I thought initially that the SGR designator was a reference to its location in the sky (which would be toward the general direction of Sagittarius or SGR), but in fact SGR is a reference to "Soft Gamma Repeater". From a much greater distance, this event would have appeared as a very high energy transient event, so it is possible that events like this can help in the explanation for Gamma Ray Bursts like GRB 090423.

Something else to lie in bed awake at night thinking about: as noted in the article abstract in the journal Nature, this object released more energy in a fifth of a second than the Sun in 250,000 years. Nature doesn't do lurid speculation, but if it had been 10 instead of 50,000 light years away, its effect for everyone on the half of the world facing it would have been equivalent to being less than 10 km away from a 12 kiloton nuclear blast. Fortunately, there are no magnetars within 10,000 light years of Earth.

No comments: