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.
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