Gamma rays

We all know what gamma rays are don’t we? They are the radiation that turned Bruce Banner into the Hulk. Ok so not strictly factual but gamma rays are radiation, part of the electromagnetic spectrum along with radio waves, infrared radiation, ultraviolet radiation, X-rays and microwaves.

French chemist Paul Villard was investigating radiation from radium in 1900 when he first observed gamma rays. However the rays were not named until a few years later when physicist Ernest Rutherford named them following the pattern Alpha, Beta, Gamma. It was not until the 1960’s that gamma rays were observed by astronomers.

Gamma-rays are in the range of the electromagnetic spectrum above soft X-rays. Gamma-rays have frequencies greater than about 1018 cycles per second, or hertz (Hz), and wavelengths of less than 100 picometers (pm), or 4 × 10-9 inches. They occupy the same region of the electromagnetic spectrum as hard X-rays. The only difference between them is their source: X-rays are produced by accelerating electrons, whereas gamma-rays are produced by atomic nuclei.

Gamma rays can be produced by stars as a result of the nuclear fusion process at their core. These super-high-energy photons are converted to lower-energy photons before they reach the surface, and are emitted out into space. Gamma-rays are the highest-energy form of light in the universe. Some are generated by transient events, such as solar flares and the huge star explosions known as supernovas. Others are produced by steady sources like the supermassive black holes at the hearts of galaxies.

The crab nebula sits in the Taurus constellation and is the resulting aftermath of an exploding star. It’s light first reached earth in 1054 having travelled 6500 light years.

Screenshot 2018-06-15 21.28.11
The Crab Nebula curtesy of Nasa. Taken by the Hubble space telescope.

At the centre of the crab nebula is a pulsar spinning 30 times per second. Since 2007, the Italian Space Agency’s AGILE satellite have detected several short-lived gamma-ray flares at energies hundreds of times higher than the nebula’s observed X-ray variations. Below is an example image of gamma rays taken by the Italian Fermi satellite.

Screenshot 2018-06-15 21.45.39

The earths atmosphere blocks most interstellar gamma rays, so observations are normally made by high altitude instruments such as balloons. Here they monitor high-energy astrophysical systems, including stellar corona’s, white dwarf stars, pulsars, black holes, supernova, galaxy clusters, and other diffuse gamma-ray background radiation,

The Compton Gamma Ray Observatory (GRO) is a sophisticated satellite observatory dedicated to observing the high-energy Universe. It is the second in NASA’s program of orbiting “Great Observatories”, following the Hubble Space Telescope. While Hubble’s instruments operate at visible and ultraviolet wavelengths, Compton carries a collection of four instruments, which together can detect an unprecedented broad range of high-energy radiation called gamma rays. These instruments are the Burst And Transient Source Experiment (BATSE), the Oriented Scintillation Spectrometer Experiment (OSSE), the Imaging Compton Telescope (COMPTEL), and the Energetic Gamma Ray Experiment Telescope (EGRET). – according to Nasa

Steve

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