Natural Radiation from Space
Victor Franz Hess (Austrian-American physicist, 1883–1964) found between 1911 and 1912 that natural radiation, energetic enough to include gamma rays, showers the Earth. We now refer to this radiation as “cosmic rays.” The term refers to the mixture of gamma rays and fast-moving particles that continuously strikes the Earth’s atmosphere. Some of the particles come from the Sun or other stars. Others are bits and pieces of atoms that happened to be in the way of gamma rays and broke up. Some of the rays are too energetic to have come from nearby stars.
There was a long debate about the source of the most energetic gamma rays. Every month or so some small region of the sky emits a burst of gamma rays. The energy of the new source fades quickly. Some astronomers thought that these burst sources must be far away, because light from them is extremely reddened like the light from the most distant galaxies. But if the burst sources are far away then while they flare up they must briefly produce more energy than an entire galaxy. This led other astronomers to think that the burst sources are objects ejected at high speed from our own galaxy. If they are close to our own galaxy they don’t need to produce such great amounts of energy to achieve the brightness we see from the Earth. Still, there was no good explanation for what shoots them away so fast. The debate went on until new data resolved[i] it in 1997. Now we know that the burst sources are very far away and produce tremendous amounts of energy. They are truly cosmic, not local.
The most energetic gamma rays come to the Earth from the most distant and oldest parts of the universe. Because they have traveled so far at the high but limited speed of light, these gamma rays are also the oldest things in the universe. At the same time we must conclude that they are not infinitely old. If the stars were uncreated and infinitely old then all the ones that could flare up and emit bursts of gamma rays would have done so long before our time.
[i] Schwarzschild, Bertram, “High-Redshift Absorption Lines Show Convincingly that Gamma-Ray Bursters Are Very Far Away,” Physics Today, 50 (Number 7, July 1997), pp. 17–18.
There was a long debate about the source of the most energetic gamma rays. Every month or so some small region of the sky emits a burst of gamma rays. The energy of the new source fades quickly. Some astronomers thought that these burst sources must be far away, because light from them is extremely reddened like the light from the most distant galaxies. But if the burst sources are far away then while they flare up they must briefly produce more energy than an entire galaxy. This led other astronomers to think that the burst sources are objects ejected at high speed from our own galaxy. If they are close to our own galaxy they don’t need to produce such great amounts of energy to achieve the brightness we see from the Earth. Still, there was no good explanation for what shoots them away so fast. The debate went on until new data resolved[i] it in 1997. Now we know that the burst sources are very far away and produce tremendous amounts of energy. They are truly cosmic, not local.
The most energetic gamma rays come to the Earth from the most distant and oldest parts of the universe. Because they have traveled so far at the high but limited speed of light, these gamma rays are also the oldest things in the universe. At the same time we must conclude that they are not infinitely old. If the stars were uncreated and infinitely old then all the ones that could flare up and emit bursts of gamma rays would have done so long before our time.
[i] Schwarzschild, Bertram, “High-Redshift Absorption Lines Show Convincingly that Gamma-Ray Bursters Are Very Far Away,” Physics Today, 50 (Number 7, July 1997), pp. 17–18.