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PASSAGE IV
Long before experiments could detect gamma-rays emitted by cosmic sources, scientists had known that the Universe should be producing such high energy photons. Hard work by several brilliant scientists had shown us that a number of different processes which were occurring in the violent Universe would result in gamma-ray emission. These processes included cosmic ray interactions with interstellar gas, supernova explosions, and interactions of energetic electrons with magnetic fields. In the 1960s, we finally developed the ability to actually detect these emissions and we have been looking at them ever since.
Gamma-rays coming from space are mostly absorbed by the Earth’s atmosphere. So, gamma-ray astronomy could not develop until, it was possible to get our detectors above all or most of the atmosphere, using balloons or spacecraft. The first gamma-ray telescope carried into orbit, on the Explorer XI satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons. These appeared to come from all directions in the Universe, implying some sort of uniform ‘gamma-ray background’. Such a background would be expected from the interaction of cosmic rays (very energetic charged particles in space) with gas found between the stars. Additional gamma-ray experiments flew on the OGO, OSO, Vela, and Russian Cosmos series of satellites. However, the first satellite designed as a ‘dedicated’ gamma-ray mission was the second Small Astronomy Satellite (SAS-2) in 1972.
It lasted only for seven months due to an electrical problem, but provided an exciting view into the high-energy Universe (sometimes called the Violent Universe, because the kinds of events in space that produce gamma-rays tend to be explosions, high-speed collisions, and such!). In 1975, the European Space Agency launched a similar satellite, COS-B, which operated until 1982. These two satellites, SAS-2 and COS-B, confirmed the earlier findings of the gamma-ray background, and also detected a number of point sources. However, the poor resolution of the instruments made it ' impossible to identify most of these point sources with individual stars or stellar systems.
Long before experiments could detect gamma-rays emitted by cosmic sources, scientists had known that the Universe should be producing such high energy photons. Hard work by several brilliant scientists had shown us that a number of different processes which were occurring in the violent Universe would result in gamma-ray emission. These processes included cosmic ray interactions with interstellar gas, supernova explosions, and interactions of energetic electrons with magnetic fields. In the 1960s, we finally developed the ability to actually detect these emissions and we have been looking at them ever since.
Gamma-rays coming from space are mostly absorbed by the Earth’s atmosphere. So, gamma-ray astronomy could not develop until, it was possible to get our detectors above all or most of the atmosphere, using balloons or spacecraft. The first gamma-ray telescope carried into orbit, on the Explorer XI satellite in 1961, picked up fewer than 100 cosmic gamma-ray photons. These appeared to come from all directions in the Universe, implying some sort of uniform ‘gamma-ray background’. Such a background would be expected from the interaction of cosmic rays (very energetic charged particles in space) with gas found between the stars. Additional gamma-ray experiments flew on the OGO, OSO, Vela, and Russian Cosmos series of satellites. However, the first satellite designed as a ‘dedicated’ gamma-ray mission was the second Small Astronomy Satellite (SAS-2) in 1972.
It lasted only for seven months due to an electrical problem, but provided an exciting view into the high-energy Universe (sometimes called the Violent Universe, because the kinds of events in space that produce gamma-rays tend to be explosions, high-speed collisions, and such!). In 1975, the European Space Agency launched a similar satellite, COS-B, which operated until 1982. These two satellites, SAS-2 and COS-B, confirmed the earlier findings of the gamma-ray background, and also detected a number of point sources. However, the poor resolution of the instruments made it ' impossible to identify most of these point sources with individual stars or stellar systems.
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