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Gamma Ray Flare (NASA Press Release)
Radsafers,
I found this at the Goddard web site for those who were interested in what
the event was. Enjoy! (Also, it's not entirely off topic as it has a
reference to human risk in the first paragraph. i.e. none as expected)
Scott Kniffin
RSO Unisys Federal Systems, Lanham, MD
CHO Radiation Effects Facility, GSFC, NASA
mailto:Scott.D.Kniffin.1@gsfc.nasa.gov
The opinions expressed here are my own. They do not necessarily represent
the views of Unisys or NASA. This material has not been reviewed by my
manager or NASA.
Tremendous Gamma-Ray
Flare Blasts Earth
Donald Savage
Headquarters, Washington, DC Sept. 29, 1998
(Phone: 202/358-1547)
Tim Tyson
Marshall Space Flight Center, Huntsville, AL
(Phone: 256/544-0994)
RELEASE: 98-172
TREMENDOUS GAMMA-RAY FLARE BLASTS EARTH
An intense wave of gamma rays, emanating from a catastrophic
magnetic flare on a mysterious star 20,000 light years away,
struck the Earth's atmosphere on August 27, 1998, providing
important clues about some of the most unusual stars in the
Universe. Scientists said the gamma radiation posed no health
risk to humans.
The wave hit the night side of the Earth and ionized (or
knocked electrons out of) the atoms in the upper atmosphere to a
level usually seen only during daytime. This astonishing blast of
ionization was detected by Prof. Umran Inan of Stanford
University. "It is extremely rare for an event occurring outside
the solar system to have any measurable effect on the Earth," Inan
said. It was so powerful that it blasted sensitive detectors to
maximum or off-scale on at least seven scientific spacecraft in
Earth orbit and around the solar system.
The wave of radiation emanated from a newly discovered type
of star called a magnetar. Magnetars are dense balls of super-
heavy matter, no larger than a city but weighing more than the
Sun. They have the greatest magnetic field known in the Universe,
so intense that it powers a steady glow of X-rays from the star's
surface, often punctuated by brief, intense gamma-ray flashes, and
occasionally by cataclysmic flares like the one observed on August
27. Astronomers think that all these effects are caused by an
out-of-control magnetic field -- a field capable of heating,
mixing, and sometimes cracking the star's rigid surface to bits.
In June a team of scientists led by Dr. Chryssa Kouveliotou
of NASA's Marshall Space Flight Center in Huntsville, AL, used
NASA's Compton Gamma Ray Observatory to detect a series of about
50 flashes from the star, a type called a Soft Gamma Repeater
(SGR), known as "SGR1900+14" in the constellation Aquila. During
the flashing episode, Kouveliotou's team, in collaboration with
Dr. Tod Strohmayer and his colleagues at NASA's Goddard Space
Flight Center, Greenbelt, MD, pointed sensitive X-ray detectors
aboard NASA's Rossi X-ray Timing Explorer satellite toward the
star. They found faint X-rays coming from the star, which pulsed
regularly in intensity every 5.16 seconds.
These 5.16-second pulses already had been detected in April,
when Dr. Kevin Hurley, University of California, Berkeley, aimed
the Japanese/NASA Advanced Satellite for Cosmology and
Astrophysics (ASCA) at the star. Comparisons of the ASCA and RXTE
data showed that the X-ray pulses were gradually slowing down.
The finding implies that the Soft Gamma Repeater has a
magnetic field about 800 trillion times stronger than Earth's
magnetic field, and about 100 times stronger than any found
anywhere in the Universe. Kouveliotou and her team had earlier
found that another SGR was also a magnetar. This was exactly what
Dr. Robert Duncan, University of Texas, Austin, and Dr.
Christopher Thompson, University of North Carolina, Chapel Hill,
predicted in 1992 when they originated the "magnetar" theory.
Before the NASA team could announce these conclusions,
SGR1900+14 emitted the tremendous flare of August 27, which was
observed by almost every spacecraft with a high-energy radiation
detector in space.
"Magnetars seem to answer several mysteries about the
structure and evolution of stars," said Kouveliotou. "We think
magnetars spend their first 10,000 years as Soft Gamma Repeaters.
As they weaken with age and slow their rotation, they become
Anomalous X-ray Pulsars -- stars that do not have enough 'juice'
to flash anymore, but which emit a steady flow of X-rays for
perhaps another 30,000 years. After that, they fade to black and
drift for eternity through the heavens. The absence of observable
pulsars in some supernova remnants just means that the pulsar's
lights have gone out sooner than we expected."
A magnetar forms from the explosion, or supernova, of a
very large, ordinary star. The star's heavy center collapses
under its own gravity into a dense ball of super-compressed matter
12 miles across. This "neutron star" consists mostly of neutrons
in a dense fluid, but the outer layers solidify into a rigid crust
of atoms about 1 mile deep, with a surface of iron.
Even with this solid crust, a magnetar is incredibly
unstable. Almost unimaginable magnetic fields, about 800 trillion
times that of Earth's, cause the crust to crack and ripple in
powerful starquakes. The energy released in these explosive
starquakes streams out into space as intense flashes of gamma-
rays. In the August 27 flare, pure magnetic energy was also
released, as the star's entire crust was broken to bits.
"A magnet this strong could erase the magnetic strip on the
credit cards in your wallet or pull the keys out of your pocket
from a distance halfway to the Moon," said Duncan.
- end -
EDITOR'S NOTE: Additional information on magnetars or the Aug. 27
event is available on the internet at:
http://www1.msfc.nasa.gov/NEWSROOM/
and
http://www.magnetars.com/
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