By Robert Roy Britt
Senior science writer

Updated: 7:21 p.m. ET Feb. 18, 2005A huge explosion halfway across the galaxy packed so much power it briefly altered Earth's upper atmosphere in December, astronomers said Friday.

No known eruption beyond our solar system has ever appeared as bright upon arrival.

But you could not have seen it, unless you can top the X-ray vision of Superman: In gamma rays, the event equaled the brightness of the full Moon's reflected visible light.

The blast originated about 50,000 light-years away and was detected Dec. 27. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers).

The commotion was caused by a special variety of neutron star known as a magnetar. These fast-spinning, compact stellar corpses -- no larger than a big city -- create intense magnetic fields that trigger explosions. The blast was 100 times more powerful than any other similar eruption witnessed, said David Palmer of Los Alamos National Laboratory, one of several researchers around the world who monitored the event with various telescopes.

Tsunami connection?
Several readers wondered if the magnetar blast could be related to the December tsunami. Scientists have made no such connection. The blast affected Earth's ionosphere, which is routinely affected to a greater extent by changes in solar activity.


"Had this happened within 10 light-years of us, it would have severely damaged our atmosphere and possibly have triggered a mass extinction," said Bryan Gaensler of the Harvard-Smithsonian Center for Astrophysics (CfA).

There are no magnetars close enough to worry about, however, Gaensler and two other astronomers told SPACE.com. But the strength of the tempest has them marveling over the dying star's capabilities while also wondering if mass extinctions in the past might have been triggered by stellar explosions.

'Once-in-a-lifetime'
The sun is a middle-aged star about 8 light-minutes from us. It's tantrums, though cosmically pitiful compared to the magnetar explosion, routinely squish Earth's protective magnetic field and alter our atmosphere, lighting up the night sky with colorful lights called aurora.

Solar storms also alter the shape of Earth's ionosphere, a region of the atmosphere 50 miles (80 kilometers) up where gas is so thin that electrons can be stripped from atoms and molecules -- they are ionized -- and roam free for short periods. Fluctuations in solar radiation cause the ionosphere to expand and contract.

"The gamma rays hit the ionosphere and created more ionization, briefly expanding the ionosphere," said Neil Gehrels, lead scientist for NASA's gamma-ray watching Swift observatory.

Gehrels said in an email interview that the effect was similar to a solar-induced disruption but that the effect was "much smaller than a big solar flare."

Still, scientists were surprised that a neutron star so far away could alter the ionosphere.

"That it can reach out and tap us on the shoulder like this, reminds us that we really are linked to the cosmos," said Phil Wilkinson of IPS Australia, that country's space weather service.

"This is a once-in-a-lifetime event," said Rob Fender of Southampton University in the UK. "We have observed an object only 20 kilometers across [12 miles], on the other side of our galaxy, releasing more energy in a tenth of a second than the sun emits in 100,000 years."