Cambridge, MA- Forget “Independence Day” or “War of the Worlds.” A monstrous
cosmic explosion last December showed that the earth is in more danger from
real-life space threats than from hypothetical alien invasions.

The gamma-ray flare, which briefly outshone the full moon, occurred within
the Milky Way galaxy. Even at a distance of 50,000 light-years, the flare
disrupted the earth’s ionosphere. If such a blast happened within 10
light-years of the earth, it would destroy the much of the ozone layer,
causing extinctions due to increased radiation.

“Astronomically speaking, this explosion happened in our backyard. If it
were in our living room, we’d be in big trouble!” said Bryan Gaensler
(Harvard-Smithsonian Center for Astrophysics), lead author on a paper
describing radio observations of the event.

Gaensler headed one of two teams reporting on this eruption at a special
press event today at NASA headquarters. A multitude of papers are planned
for publication.

The giant flare detected on December 27, 2004, came from an isolated, exotic
neutron star within the Milky Way. The flare was more powerful than any
blast previously seen in our galaxy.

“This might be a once-in-a-lifetime event for astronomers, as well as for a
neutron star,” said David Palmer of Los Alamos National Laboratory, lead
author on a paper describing space-based observations of the burst. “We know
of only two other giant flares in the past 35 years, and this December event
was one hundred times more powerful.”

NASA’s newly launched Swift satellite and the NSF-funded Very Large Array
(VLA) were two of many observatories that observed the event, arising from
neutron star SGR 1806-20, about 50,000 light years from Earth in the
constellation Sagittarius.

Neutron stars form from collapsed stars. They are dense, fast-spinning,
highly magnetic, and only about 15 miles in diameter. SGR 1806-20 is a
unique neutron star called a magnetar, with an ultra-strong magnetic field
capable of stripping information from a credit card at a distance halfway to
the Moon. Only about 10 magnetars are known among the many neutrons stars in
the Milky Way.

“Fortunately, there are no magnetars anywhere near the earth. An explosion
like this within a few trillion miles could really ruin our day,” said
graduate student Yosi Gelfand (CfA), a co-author on one of the papers.

The magnetar’s powerful magnetic field generated the gamma-ray flare in a
violent process known as magnetic reconnection, which releases huge amounts
of energy. The same process on a much smaller scale creates solar flares.

“This eruption was a super-super-super solar flare in terms of energy
released,” said Gaensler.

Using the VLA and three other radio telescopes, Gaensler and his team
detected material ejected by the blast at a velocity three-tenths the speed
of light. The extreme speed, combined with the close-up view, yielded
changes in a matter of days.

Spotting such a nearby gamma-ray flare offered scientists an incredible
advantage, allowing them to study it in more detail than ever before. “We
can see the structure of the flare’s aftermath, and we can watch it change
from day to day. That combination is completely unprecedented,” said
Gaensler.

Headquartered in Cambridge, Mass., the Harvard-Smithsonian Center for
Astrophysics (CfA) is a joint collaboration between the Smithsonian
Astrophysical Observatory and the Harvard College Observatory. CfA
scientists, organized into six research divisions, study the origin,
evolution and ultimate fate of the universe.