Compton Gamma Ray Observatory

Compton Telescope / Gamma Ray Observatory

It’s not every day that scientists find an entirely new class of objects in the Universe. But, that is exactly what astrophysicist Neil Gehrels and his team at NASA Goddard Space Flight Center discovered using the Compton Gamma Ray Observatory (CGRO).

The objects they discovered were different from other sources of gamma rays the team typically studied. Gamma rays are usually emitted in sudden bursts that appear without warning from any part of the sky. However, these objects emitted gamma rays on a continuous basis. Their existence delighted and baffled the Goddard scientists.

"These are objects we've never seen before," Dr. Gehrels said. "We can't make out what they are yet, but we know they're different and, boy, there's a lot of them."

The Compton telescope, the second of NASA's four Great Observatories, was launched in 1991 to study gamma rays, which is the most powerful form of radiation in the Universe. The other Great Observatories include the Hubble Space Telescope, the Chandra X-ray Observatory, and the Spitzer Space Telescope.

The observatory was named after Dr. Arthur Holly Compton, who won the Nobel Prize in physics for developing a process of scattering high-energy photons by electrons that is essential to detecting gamma rays.

During its nine years in orbit, the telescope revolutionized our understanding of gamma rays and other phenomena. The Compton observatory studied gamma-ray bursts, black holes, quasar emissions, solar flares, pulsars, and supernova explosions.

The Compton Gamma Ray Observatory was composed of four main instruments, each measuring gamma-ray radiation in a different band. These instruments were the Burst and Transient Source Experiment (BATSE), Imaging Compton Telescope (COMPTEL), Energetic Gamma Ray Experiment Telescope (EGRET), and Oriented Scintillation Spectrometer Experiment (OSSE).

The EGRET instrument was able to identify 271 sources of gamma-ray emissions, 170 of which were unidentified. One of EGRET’s major discoveries was blazars, which are quasars that emit gamma rays. The instrument also discovered five gamma-ray pulsars.

The BATSE instrument detected an average of one gamma ray burst event per day, for a total of 2,700 events over the lifetime of the Compton Gamma Ray Observatory. Scientists were able to use these data to determine that the majority of gamma-ray bursts originate in distant galaxies, not in our Milky Way galaxy.

On Jan. 23, 1999, scientists were able for the first time to observe the visible light that is emitted along with a gamma-ray burst. BATSE detected the burst and transmitted information to the ground, which forwarded it on to observatories around the world via the Internet. Scientists were able to monitor the burst, which had the power of nearly ten million billion suns, in different wavelengths.

"This discovery signals yet another new era in the study of these fantastic objects,” said Dr. Jerry Fishman, principal investigator for BATSE. “It is now shown that they can be observed from the ground, in different wavelength regions, while the main part of the explosion is in progress.”

The Compton Gamma Ray Observatory was intentionally de-orbited over an uninhabited part of the ocean on June 4, 2000, after one of its control gyroscopes failed. Although the telescope was still operating, controllers would have had a difficult time de-orbiting it safely if another gyroscope failed. It was a sad, premature end to a mission that helped rewrite the astronomy textbooks.

Links for Compton Telescope / Gamma Ray Observatory

Compton Gamma Ray Observatory website

 

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