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2008-06-04 05:37:38
Charles Q. Choi
Special to LiveScience
SPACE.comTue Jun 3, 7:31 AM ET
By scanning the universe for the most powerful form of radiation known, the
Gamma-Ray Large Area Space Telescope (GLAST) could shed light on dark matter,
microscopic black holes and other cosmic enigmas.
In fact its greatest promise is that it might discover something nobody is even
looking for.
Gamma rays are the highest energy form of light, created under some of the most
violent events in the universe, such as the death of stars or the annihilation
of matter. GLAST is the first gamma-ray observatory to survey the entire sky
every day with unprecedented sensitivity, and the hope is that it will open a
dramatic new window onto the cosmos. This multi-agency, multi-national effort
is working toward a launch on June 7.
"If you could see the sky with gamma-ray eyes, it would look entirely different
from the night sky now," said Steve Ritz, the GLAST project scientist and an
astrophysicist at NASA's Goddard Space Flight Center in Greenbelt, Md. "Gamma
rays are emitted in the most extreme environments in the universe, where the
gravitational and electric and magnetic fields are so much higher than anything
you could ever study directly on Earth.
For example, GLAST could help find dark matter, the as yet unseen substance
that could make up 90 percent of all matter in the universe, whose presence
scientists infer by its effects on the motion of galaxies. In theory, dark
matter particles are their own antiparticles, meaning they destroy each other
when they come into contact.
The annihilation of dark matter would result in gamma rays with energies
specific to the masses of the obliterated particles, "a signature that would be
unmistakable," Ritz said. "There are a lot of mysteries about what dark matter
is, how densely it is distributed, and where in the galaxy it clumps that GLAST
could help answer."
Tiny black holes
GLAST may also detect microscopic black holes that may have formed right after
the Big Bang. No one is sure if any exist, but if they did and have survived
until now, they could be smaller than a proton but have the mass of Mt.
Everest. All black holes theoretically evaporate at least some of their mass
away as energy, and microscopic black holes could in theory vanish completely
in an explosion of sundry particles and gamma rays that GLAST could detect.
"If these microscopic black holes exist and they evaporated, there would be
this rising pulse of gamma rays that would then go to zero, and that's never
been seen before, so that would be a very distinct signal," said Chip Meegan,
GLAST Burst Monitor principal investigator and an astrophysicist at NASA's
Marshall Space Flight Center, in Huntsville, Ala.
At least once a day, the universe is rocked by the mightiest explosions known
blasts of incredibly powerful gamma rays. The engine that powers these gamma
ray bursts is unknown, but they seem to emerge during the births of black
holes, or during the mergers of neutron stars with black holes or other neutron
stars.
"We don't really understand the physics involved because it's so complicated,
since you're releasing a lot of energy in such a short time they can each
release as much energy in a few seconds as the sun does in its entire 10
billion year lifetime," Meegan said. "Hopefully we'll be able to study whole
new aspects of gamma ray bursts that we didn't before."
The super-massive black holes at the center of galaxies which have as much as
billions of times the mass of our sun also generate incredible amounts of
gamma rays. As they rip stars apart, they spew out jets of hot gas moving near
the speed of light that emit gamma rays. By analyzing this radiation, GLAST
could help solve the mystery of how these jets are made, and therefore yield
insights on how black holes affect the space around them.
"We want to understand how these super-massive black holes work, how they got
there, and how they can accomplish feats of such power," Ritz said. "We're
really just beginning to understand them."
Light's speed
GLAST could also help see if the speed of light really is constant regardless
of wavelength. According to Einstein's theory of relativity, all light travels
at the same speed, but some recent theories suggest that extremely high-energy,
short-wavelength gamma rays might experience a turbulence of sorts in
space-time from virtual matter repeatedly forming and disappearing. As such,
their speed might vary slightly over the course of billions of light years,
making them arrive just before or after lower-energy rays from the same gamma
ray burst.
"If this effect exists, it's not something that you could really see on Earth,"
Ritz said. "You'd essentially want to see how light does on a long-distance
race, and that's billions of light years. But gamma ray bursts are so bright
that you could see them from such vast distances. GLAST could really see these
time differences."
Perhaps most exciting is the possibility that GLAST will find something no one
is expecting. This space telescope can peer a range of high-energy gamma rays
that is virtually unexplored.
"There's such a leap forward in capabilities with GLAST that we have a really
good chance of discovering things not even on the list yet," Ritz said.
This space observatory's Large Area Telescope can see a fifth of the sky at any
given moment with unparalleled sensitivity for gamma rays. To improve it
further, the GLAST Burst Monitor constantly sees in all directions at once to
watch for sudden flares of gamma rays produced by gamma ray bursts and solar
flares. GLAST will circle some 340 miles above the Earth to view gamma rays
unimpeded by the atmosphere, completing an orbit every 95 minutes and viewing
the entire sky every two orbits.
GLAST will receive a new name once in orbit, chosen from some 12,000
suggestions given by the general public around the world. The space telescope's
first basic results might come out as soon as three months afterward.
The mission is scheduled for liftoff atop a Delta 2 rocket at 11:45 a.m. EDT on
June 7. The mission has been delayed twice because of technical issues with the
booster.