Brightest galactic flash ever detected hits Earth

Some researchers have speculated that one or more known mass extinctions hundreds of millions of years ago might have been the result of a similar blast altering Earth's atmosphere. There is no firm data to support the idea, however. But astronomers say the sun might have been closer to other stars in the past.

A similar blast within 10 light-years of Earth "would destroy the ozone layer," according to a CfA statement, "causing abrupt climate change and mass extinctions due to increased radiation."

The all-clear has been sounded, however.

"None of the known sample [of magnetars] are closer than about 4,000-5,000 light years from us," Gaensler said. "This is a very safe distance."

Cause a mystery
Researchers don't know exactly why the burst was so incredible. The star, named SGR 1806-20, spins once on its axis every 7.5 seconds, and it is surrounded by a magnetic field more powerful than any other object in the universe.

"We may be seeing a massive release of magnetic energy during a 'starquake' on the surface of the object," said Maura McLaughlin of the University of Manchester in the UK.

Another possibility is that the magnetic field more or less snapped in a process scientists call magnetic reconnection.

Gamma rays are the highest form of radiation on the electromagnetic spectrum, which includes X-rays, visible light and radio waves too.

The eruption was also recorded by the National Science Foundation's Very Large Array of radio telescopes, along with other European satellites and telescopes in Australia.

Explosive details
A neutron star is the remnant of a star that was once several times more massive than the sun. When their nuclear fuel is depleted, they explode as a supernova. The remaining dense core is slightly more massive than the sun but has a diameter typically no more than 12 miles (20 kilometers).

Millions of neutron stars fill the Milky Way galaxy. A dozen or so are ultra-magnetic neutron stars -- magnetars. The magnetic field around one is about 1,000 trillion gauss, strong enough to strip information from a credit card at a distance halfway to the moon, scientists say.

Of the known magnetars, four are called soft gamma repeaters, or SGRs, because they flare up randomly and release gamma rays. The flare on SGR 1806-20 unleashed about 10,000 trillion trillion trillion watts of power.

"The next biggest flare ever seen from any soft gamma repeater was peanuts compared to this incredible Dec. 27 event," said Gaensler of the CfA.

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