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Question and Answer with GLAST Scientists
NASA's Gamma-ray Large Area Space Telescope (GLAST) will scan the sky for high-energy photons.
NASA / GSFC
GLAST is a specially tuned instrument designed to explore the most extreme environments in the universe — the places where nature harnesses energies far beyond anything on Earth. Its many goals include the search for dark matter and the quest to understand how black holes accelerate jets of material to nearly the speed of light. GLAST aims to help crack the mysteries of gamma-ray bursts and it will answer long-standing questions across a broad range of fields, including solar flares, pulsars, and the origin of cosmic rays.
In our live question-and-answer session, GLAST project scientist Steve Ritz and GLAST deputy project scientist Dave Thompson answered your questions about the mission, high-energy astrophysics, and much more — all in real-time.
To learn more about GLAST, be sure to read the June issue of Sky & Telescope magazine, on newsstands now.
Q
Mark W. Finn; Dillon, Colorado, USA
What nickname have you given the GLAST?
A
Dave Thompson (Greenbelt, MD)
Thanks for the question. As you may know, there was a Web suggestion box for new names for GLAST after launch.
Over 12,000 suggestions came in from all over the world (maybe one was yours!). NASA is sorting through all those suggestions and will announce the new name after the observatory is on orbit and operating.
Q
Royce Halden, Cinti, Ohio / USA
How long after launch will it take for GLAST to start producing science results?
A
Steve Ritz (Greenbelt, MD)
We're looking forward to science results, too! After launch, it will take about 60 days to turn on and check out the observatory. After that, science results will start appearing quite quickly. You can find a summary timeline on our web page here: http://www.nasa.gov/pdf/226365main_GLAST_Yr1_Timeline.pdf, also linked to our page http://www.nasa.gov/glast.
Q
Doug Zubenel (De Soto, Kansas)
Will this instrument be able to detect emissions from pre-visual supernovae in nearby galaxies?
A
Dave Thompson (Greenbelt, MD)
Yes, in some cases. The GLAST LAT instrument is far more sensitive than previous gamma-ray telescopes in the high-energy range, and it will survey the sky every three hours, so anything that produces gamma-ray emission is potentially detectable. Some gamma-ray bursts, for example, are probably pre-visual supernova emissions, but most supernovae do not produce gamma-ray bursts.
Q
Karen Smertz, Coalinga, CA
how close to a GRB would Earth have to be for the blast to be fatal to life here?
A
Dave Thompson (Greenbelt, MD)
There was a Sky and Telescope article about this topic in 1998 by one of our colleagues. You might look at that. Although there are many uncertainties, including the beaming, a gamma-ray burst originating on our side of the Milky Way and pointing toward us would be a significant threat.
Q
TomWilliams Bowie, MD / USA
Doesn't the Swift satellite do similar things? If so, how will this be different?
A
Steve Ritz (Greenbelt, MD)
Both GLAST and Swift study gamma-ray bursts (GRBs), but they do it in different and complementary ways. Whereas Swift observes bursts in different wavelengths (optical-UV, xray, and low-energy gamma rays) and gives precise locations, GLAST will make breakthrough measurements in a very high energy band. In fact, GLAST will be the first observatory to cover 7 decades in energy (if GLAST were a piano it would have 23 octaves!). Those breakthrough measurements will tell us about the total energy budget in GRBs. Thus, while Swift tells us where the bursts occur, GLAST will tell us more about how the underlying engines work.
Q
George Johnston (Houston, TX)
I understand that GLAST will be used for solar research too. How?
A
Dave Thompson (Greenbelt, MD)
Although the Sun is not normally very bright in gamma rays (the Moon is usually brighter), solar flares are powerful eruptions that can produce gamma-ray signatures of what produces these flares. GLAST will complement RHESSI and other solar observatories by studying the most energetic radiation from these flares.
Q
jack leibee Derwood MD
How far out in space have black holes been observed? Can GLAST do better?
A
Dave Thompson (Greenbelt, MD)
That's a great question! We know that quasars (which are thought to be powered by black holes) have been seen out to a redshift more than 6, or about
12 billion light years. In principle, GLAST can see quasars beyond that, but there are two qualifiers:
1. We do not know how far back in time such black holes exist; and 2. The gamma rays themselves do not tell us the distance, so we would require observations in the optical or infrared to confirm the distance.
Q
Ben E. Munde, Hunsville, AL
Did any of the results or operational strategies from previous gamma-ray missions (Compton, HETE 2, etc) affect the design of GLAST? Did you makes any changes based on what you learned from those flights?
A
Steve Ritz (Greenbelt, MD)
Yes, the GLAST design was very much driven by knowledge obtained from previous missions. We learned that the gamma-ray sky is incredibly variable, with large changes occurring on all timescales. One of the big advances of GLAST is the very large field of view of the instruments. The LAT sees 20% of the sky at any instant, and every two orbits (or about 3 hours) the LAT will observe the entire sky.
The GBM has an even larger field of view, covering the entire sky not occulted by the earth. We also know that the high-energy band (from 10 GeV to 100 GeV, or about 10-100 billion times the energy of visible
light) is an especially important new band for studies across a broad range of science topics. The LAT design specifically provides for much greater sensitivity in this band. In fact, the LAT provides significant advances in all key capabilities, opening a great discovery opportunity.
Q
Darold Gaffney Titusville, FL/ USA
My question is about Dark Matter - How does GLAST "see" dark matter? What do you think GLAST will tell us about it? I think the concept of dark matter is pretty interesting...
A
Steve Ritz (Greenbelt, MD)
We don't know what actually composes the dark matter (which, of course, is what makes it so interesting), but many scientists surmise the existence of weakly interacting massive particles (or WIMPs) that would have been produced in the early universe. The WIMPs are stable, but when they run into each other, their enormous rest mass can be converted into energetic particles, including gamma rays. Thus, any large density of dark matter may be glowing gamma rays, and GLAST has a great new capability to find and identify this glow. The center of our galaxy provides an excellent opportunity and there may be other detectable clumps of dark matter elsewhere. Of course, the challenge will be to prove the signal is from dark matter, and not from other astrophysical processes, but we're looking forward to that! This is a particularly exciting time in dark matter research. The same hypothetical massive particles may also soon be produced at the new Large Hadron Collider (LHC) that is about to start operating, and exquisitely sensitive underground detectors are also looking for rare signals of the dark matter particles colliding with ordinary matter as they pass through the earth. All these techniques work together to fill in the pieces of this important puzzle.
Q
Cameron Martus (Cincinnati, OH)
Will GLAST be used for quasar research? What can be discovered about quasars using gamma rays?
A
Dave Thompson (Greenbelt, MD)
Yes, quasars will be a primary topic for GLAST, especially the Large Area Telescope. The sub-class of quasars known as blazars are ones with a jet pointed right at Earth. The gamma rays help us learn how a black hole, which draws matter in, can also power a jet of particles and radiation squirting outwards. One particular question gamma rays can help with is the composition of the jet - is it mostly protons or mostly electrons?
Q
David Tytell (Boston, MA)
Where can S&T readers find out more about GLAST?
A
Steve Ritz (Greenbelt, MD)
Please visit our website at http://www.nasa.gov/glast. There, you can find more information about the mission, up-to-date status reports, and pictures. NASA’s GLAST mission is an astrophysics and particle physics partnership, developed in collaboration with the U.S.
Department of Energy, along with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden, and the United States.
Thanks very much for all the great questions and your interest in GLAST!
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