Imagine the Universe!

High-Energy Gamma-Ray Instrument Design

Looking at the Sky in a New Light

Suppose you wanted to take pictures of the sky in gamma-ray light. These pictures would reveal the violent, explosive face of the Universe, because gamma-rays are the most powerful type of light. In fact, gamma-rays are so energetic that they behave more like particles than waves. For example, there are no gamma-ray mirrors or lenses. Gamma-ray telescopes cannot focus gamma-rays, so they must have large detecting areas. Because of the power of gamma-rays, these telescopes must also be massive to stop all that energy. Yet despite their energy, gamma-rays cannot penetrate the earth's atmosphere; gamma-ray astronomy is mostly carried out from space. Much of the research in gamma-ray astronomy is devoted to finding better ways to take gamma-ray pictures of the sky.

EGRET allsky image

EGRET All-Sky Map

Collecting these photons is HARD. There are just not that many of them around. The technology that is used is basically that of particle accelerators here on Earth (that is the only source here of lots of gamma-rays, for testing and calibration, for example).

Tell Me How to Detect Elusive Gamma-Rays

What Else Makes Observing Gamma-Rays Hard?

Tell Me About Flying Gamma-Ray Detectors On Balloons

Gamma-Ray Telescopes on CGRO

Four gamma-ray experiments are now working on board the Compton Gamma Ray Observatory satellite, a huge satellite launched from the Space Shuttle in 1991. These experiments are studying a wide range of violent processes and objects in the Universe: pulsars, quasars, supernovae, collisions between cosmic rays and gas molecules, gamma-ray bursts, and many stars or galaxies that remain mysteries.

Tell me moreabout the instruments on board CGRO (

Future Projects

Because gamma-ray telescopes on the Compton Observatory were designed in the 1970s, they cannot take pictures that are as clear as radio, optical, or X-ray telescopes. New ways to detect and measure gamma-rays have been developed since then, and so a group at GSFC and other gamma-ray astronomers are now planning new telescopes that will help solve some of the gamma-ray mysteries. One of these new telescopes, called INTEGRAL (, is being built by European scientists with help from some U.S. scientists. It will study many of the sources of gamma-rays like supernovae. Other gamma-ray telescopes being developed, like one called GLAST (*, which will make maps of the whole sky with much higher resolution than the current telescopes. These telescopes should bring the picture of the gamma-ray sky into better focus, letting scientists see the high-energy Universe far more clearly.

Some other things that are currently being developed/explored are observing nuclear lines. These lines (at low gamma-ray energies) are similar to the emission lines caused by electron transitions when an element is heated up, but they are much higher energies and they come from nuclear transitions when an element is really heated up (i.e. very very close to a black hole, for example). These are unique probes into areas that would not otherwise be accessible.

*GLAST launched on June 11, 2008.

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Thank you to David Thompson for contributing to this article.

Imagine the Universe is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA's Goddard Space Flight Center.

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Acting Project Leader: Dr. Barbara Mattson
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