An international team of
astronomers is eagerly awaiting the launch of a new orbital observatory that
will hopefully shed light on the most powerful explosions in the
universe.
Just eight days away from launch,
NASA's Swift spacecraft is being readied for a mission to scan the sky for
gamma-ray bursts, cosmic explosions that can burn with the intensity of billions
of suns in less than a second. Researchers hope the mission will identify the
trigger that sets off the bursts.
"I'm very anxious to get up there
and start doing the science," said Swift's principal investigator Neil Gehrels,
of NASA's Goddard Space Flight Center (GSFC), in a telephone interview with SPACE.com. "It's one of the most
exciting things of my life."
As its name implies, the Swift
mission is designed for speed. Equipped with three telescopes to first detect -
then observe - gamma-ray bursts, the spacecraft is designed to automatically
detect the first flash of an explosion and then target itself at the event in
about one minute.
That's faster than any other
satellite or ground-based system to date.
"[Swift] is the most autonomous
spacecraft NASA has ever built," explained Tim Gehringer, Swift's deputy project
manager at GSFC, during a prelaunch mission briefing earlier this month. "It's a
smart, capable spacecraft."
Swift is currently slated to ride a
Delta 2 rocket into orbit on Nov. 17 at 12:09 p.m. EST (1709 GMT) in a launch
staged from Cape Canaveral Air Force Station in Florida. NASA, the Italian Space
Agency and the Particle Physics and Astronomy Research Council in the U.K shared
the mission's total cost of about $250 million.
Solving the GRB
mystery
Gamma-ray bursts, or GRBs, can be as
long as a few minutes or as short as a few milliseconds, shedding intense
gamma-rays in the initial explosion with an afterglow of X-rays and optical
light that can fade over hours or weeks.
From Earth's vantage point such
bursts occur about once a day or so, and researchers believe the explosions are
the death knells of massive stars that could then collapse into neutron stars or
black holes.
"We think these bursts are the birth
cries of black holes," Gehrels said during the Nov. 1 prelaunch briefing, adding
that exploring the GRB-black hole connection is one of Swift's primary goals.
"If you had gamma-ray glasses and looked out at the sky, gamma-ray bursts would
dominate your experience."
GRBs could also be triggered through
more exotic means, such as the merging of two neutron stars or a black hole pair
in orbit around one another.
Swift researchers hope their
spacecraft will detect about one or two GRBs a week, or about 100 a
year.
"We have now only been able to
observe a couple of dozen or so bursts [total]," explained Swift mission
operations director John Nousek, of Penn State University, during the
briefing.
Researchers hope Swift may
ultimately detect a total of about 500 bursts throughout the satellite's
multi-year lifetime. The spacecraft's nominal mission spans two years, though it
has an orbital lifetime of between eight and possibly 15 years, Gehrels told SPACE.com.
Self-targeting
spacecraft
To find the GRB trigger, Swift will
use its primary Burst Alert Telescope - laden with 32,000 detectors - to scan
one-sixth of the sky at a time for GRB explosions.
Once detected, the spacecraft can
determine the burst's location in space and reorient itself accordingly between
20 and 75 seconds. It should then use a follow-up X-ray telescope and
optical-ultraviolet instrument for additional measurements.
The observatory won't keep the find
to itself either.
"We have more than 40 observatories,
space- and ground-based, to work with the Swift team to distribute this
information," Nousek said. "This rapid response is imperative."
The spacecraft will be in continuous
contact with ground controllers and relay its GRB find through the Gamma-ray
Burst Coordinates Network (GCN) for distributions to telescopes, researchers and
the public-at-large.
"This mission will generate the most
comprehensive data set that we've ever had on GRBs," Gehrels said. "Not only are
we going to learn what causes the bursts, but we'll be able to define a greater
number of subclasses of bursts."
For example, extremely short bursts
lasting just fractions of a second are still a total mystery for Swift to study,
especially since afterglows have so far only been detected in bursts lasting two
seconds or more, researchers said.
The early universe
Swift may also offer researchers a
glimpse at first stars to shine - and explode - in the
universe.
Because GRBs are so bright, their
gamma-ray signals can be detected from billions of light-years away, NASA
researchers said. One light-year is the distance light travels in a year, about
6 trillion miles (10 trillion kilometers).
"We could be seeing bursts from the
first generations of stars," Gehrels said, adding that the heavy metal cores of
such objects could make them more effective black hole generators. "These might
be the most distant objects we have ever seen."
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