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Cosmic Explosion Among the Brightest in Recorded
History

02.18.05

Scientists have detected a
flash of light from across the Galaxy so powerful that it
bounced off the Moon and lit up the Earth's upper atmosphere.
The flash was brighter than anything ever detected from beyond
our Solar System and lasted over a tenth of a second. NASA and
European satellites and many radio telescopes detected the
flash and its aftermath on December 27, 2004. Two science
teams report about this event at a special press event today
at NASA headquarters. A multitude of papers are planned for
publication.

Image/animation above: Image 1:
Artist conception of the December 27, 2004 gamma ray flare
expanding from SGR 1806-20 and impacting Earth’s atmosphere.
Click on image to view animation (no audio). Credit:
NASA

The scientists said the light came from a
"giant flare" on the surface of an exotic neutron star, called
a magnetar. The apparent magnitude was brighter than a full
moon and all historical star explosions. The light was
brightest in the gamma-ray energy range, far more energetic
than visible light or X-rays and invisible to our
eyes.

Such a close and powerful eruption raises the
question of whether an even larger influx of gamma rays,
disturbing the atmosphere, was responsible for one of the mass
extinctions known to have occurred on Earth hundreds of
millions of years ago. Also, if giant flares can be this
powerful, then some gamma-ray bursts (thought to be very
distant black-hole-forming star explosions) could actually be
from neutron star eruptions in nearby galaxies.

Image/animation above: Image 2:
An artist conception of the SGR 1806-20 magnetar including
magnetic field lines. After the initial flash, smaller
pulsations in the data suggest hot spots on the rotating
magnetar’s surface. The data also shows no change in the
magentar’s rotation after the initial flash. Click on image
to view animation (no audio). Credit: NASA

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.

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

Image/animation above: Image 3:
Radio data shows a very active area around SGR1806-20. The
Very Large Array radio telescope observed ejected material
from this Magnetar as it flew out into interstellar space.
These observations in the radio wavelength start about 7 days
after the flare and continue for 20 days. They show SGR1806-20
dimming in the radio spectrum. Click on image to view
animation (no audio). Credit: NRAO/CfA/Gaensler &
Univ. of Hawaii.

Dr. Bryan Gaensler of the
Harvard-Smithsonian Center for Astrophysics in Cambridge,
Mass., is lead author on a report describing the VLA
observation, which tracked the ejected material as it flew out
into interstellar space. Other key scientific teams are
associated with radio telescopes in Australia, The
Netherlands, United Kingdom, India and the United States, as
well as with NASA's High Energy Solar Spectroscopic Imager
(RHESSI).

A neutron star is the core remains of a star
once several times more massive than our Sun. When such stars
deplete their nuclear fuel, they explode -- an event called a
supernova. The remaining core is dense, fast-spinning, highly
magnetic, and only about 15 miles in diameter. Millions of
neutron stars fill our Milky Way galaxy.

Image/animation above: Image 4:
SGR-1806 is an ultra-magnetic neutron star, called a magnetar,
located about 50,000 light years away from Earth in the
constellation Sagittarius. Click on image to view animation
(no audio). Credit: NASA

Scientists have
discovered about a dozen ultrahigh-magnetic neutron stars,
called magnetars. The magnetic field around a magnetar is
about 1,000 trillion gauss, strong enough to strip information
from a credit card at a distance halfway to the moon.
(Ordinary neutron stars measure a mere trillion gauss; the
Earth's magnetic field is about 0.5 gauss.)

Four of
these magnetars are also called soft gamma repeaters, or SGRs,
because they flare up randomly and release gamma rays. Such
episodes release about 10^30 to 10^35 watts for about a
second, or up to millions of times more energy than our Sun.
For a tenth of a second, the giant flare on SGR 1806-20
unleashed energy at a rate of about 10^40 watts. The total
energy produced was more than the Sun emits in 150,000 years.

Image/animation above: Image 5:
Swift is a first-of-its-kind multi-wavelength observatory
dedicated to the study of gamma ray burst (GRB) science. Its
three instruments will work together to observe GRBs and
afterglows in the gamma ray, X-ray, ultraviolet, and optical
wavebands. Swift is designed to solve the 35-year-old mystery
of the origin of gamma-ray bursts. Scientists believe GRB are
the birth cries of black holes. Click on image to view
animation (no audio). Credit: NASA

"The
next biggest flare ever seen from any soft gamma repeater was
peanuts compared to this incredible December 27 event," said
Gaensler. "Had this happened within 10 light years of us, it
would have severely damaged our atmosphere. Fortunately, all
the magnetars we know of are much farther away than
this."

A scientific debate raged in the 1980s over
whether gamma-ray bursts were star explosions from beyond our
Galaxy or eruptions on nearby neutron stars. By the late 1990s
it became clear that gamma-ray bursts did indeed originate
very far away and that SGRs were a different phenomenon. But
the extraordinary giant flare on SGR 1806-20 reopens the
debate, according to Dr. Chryssa Kouveliotou of NASA Marshall
Space Flight Center, who coordinated the multiwavelength
observations.

Image/animation above: Image 6:
NASA's Swift satellite was successfully launched Saturday,
November 20, 2004 from the Cape Canaveral Air Force Station,
Fla. Click on image to view animation. Credit:
NASA

A sizeable percentage of "short" gamma-ray
bursts, less than two seconds, could be SGR flares, she said.
These would come from galaxies within about a 100 million
light years from Earth. (Long gamma-ray bursts appear to be
black-hole-forming star explosions billions of light years
away.)

"An answer to the 'short' gamma-ray burst
mystery could come any day now that Swift is in orbit", said
Swift lead scientist Neil Gehrels. "Swift saw this event after
only about a month on the job."

Image left: High resolution,
wide-field image of the area around SGR1806-20 as seen in
radio wavelength, without a location arrow. Credit: University
of Hawaii. Image right: A high resolution, wide-field
image of the area around SGR1806-20 as seen in radio
wavelength. SGR1806-20 can not be seen in this image generated
from earlier radio data taken when SGR1806-20 was “radio
quiet.” The arrow locates the position of SGR1806-20 within
the image. Credit: University of Hawaii.

Scientists around the world have been following
the December 27 event. RHESSI detected gamma rays and X-rays
from the flare. Drs. Kevin Hurley and Steven Boggs of the
University of California, Berkeley, are leading the effort to
analyze these data. Dr. Robert Duncan of the University of
Texas at Austin and Dr. Christopher Thompson at the Canadian
Institute for Theoretical Astrophysics (University of Toronto)
are the leading experts on magnetars, and they are
investigating the "short duration" gamma-ray burst
relationship.

Brian Cameron, a graduate student at
Caltech under the tutorage of Prof. Shri Kulkarni, leads a
second scientific paper based on VLA data. Amateur astronomers
detected the disturbance in the Earth's ionosphere and relayed
this information through the American Association of Variable
Star Observers (http://www.aavso.org).

Image above: SGR 1806-20 is a
"magnetar": a rapidly spinning neutron star that not only has
an incredible density, trillions of times greater than than
ordinary matter, but an incredibly strong magnetic field. Tens
of thousands of years ago, a "starquake" fractured the
magnetar's surface. The result was an explosive release of
energy, which sent a pulse of gamma rays racing across the
cosmos at the speed of light. Behind them came the explosion's
fireball, expanding in a lopsided fashion at roughly one-third
the speed of light. The gamma rays swept past the Earth on
December 27, 2004, when they were detected by NASA's Swift
satellite. That initial signal faded away within minutes. But
then came a steady stream of radio waves from the fireball.
Astronomers rushed to ground-based radio telescopes such as
NSF's Very Large Array outside Socorro, New Mexico, where they
have been studying the information-rich signal ever since.
Click on image to view animation (no audio). Credit:
NSF

Other observatories and scientific
representatives include:

Westerbork Synthesis Radio
Telescope, Netherlands -- Prof. Ralph Wijers
http://www.astron.nl/p/observing.htm

Molonglo
Observatory Synthesis Telescope (MOST), Australia -- Prof.
Dick Hunstead
http://www.physics.usyd.edu.au/astrop/most/

Australia
Telescope Compact Array -- Prof. Bryan Gaensler
http://www.narrabri.atnf.csiro.au/

Parkes
radio telescope, Australia -- Dr. Maura McLaughlin
http://www.parkes.atnf.csiro.au/

Greenbank
Radio Telescope, West Virginia -- Dr. Maura McLaughlin
http://www.gb.nrao.edu/

Very
Long Baseline Array, USA -- Dr. Mike Garrett
http://www.vlba.nrao.edu/

Multi-Element
Radio Linked Interferometer Network (MERLIN), UK -- Dr. Rob
Fender
http://www.merlin.ac.uk/

Additional
information about magentars and soft gamma ray repeaters can
be found at Dr. Robert Duncan’s web site located at the
University of Texas at Austin: http://solomon.as.utexas.edu/~duncan/magnetar.html

High Resolution Images:

+ Animation
1 still - beginning of the animation
+ Animation
1 still - end of animation
+ Animation
2 -- 1st still
+ Animation
2 -- 2nd still
+ Animation
4 still
+ Swift
Spacecraft
+ SGR
1806-20 (no arrow)
+ SGR
1806-20 (with arrow)

Christopher Wanjek
Goddard Space Flight
Center

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Editor: Lynn Jenner
NASA
Official: Brian Dunbar
Last Updated: February 25, 2006
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