Gamma-ray astronomy

Gamma-ray astronomy gamma-ray astronomy, or the exploration of space by means of gamma-ray detectors. Due to the much higher energy region of the gamma rays (> 500 keV ) compared to visible light ( ~ 1 electron volt ) and, consequently, also of the sometimes very different causes, the gamma-ray astronomy, gives insights into new phenomena in the Universe, particularly huge explosions and collisions of stars and other celestial bodies. The gamma-ray astronomy thus opened a window in all other areas of astronomy.

• 2.1 beginnings
• 2.2 Gamma satellite
• 2.3 gamma telescopes on the ground

Basics

Space-based gamma-ray astronomy

This branch of astronomy is still relatively young, as it is not possible on earth to absorb gamma rays from space, as they are absorbed by the Earth's atmosphere. Scientists who want to study gamma ray sources in space must, therefore, rely on appropriate observatories orbiting satellites to the earth. However, it is not possible outside the Earth's atmosphere, to monitor gamma ray sources, such as visible light by a lens or mirror telescope, since these high-energy rays are not refracted by lenses and are not reflected by mirrors. Therefore used sandwiched superimposed scintillation counters are where generated by a particular material flashes of light during the passage of a gamma photon: the flashes of light are measured by a photomultiplier or semiconductor detectors, their track possible by the detector stack a rough direction estimation of the incident gamma photon at a few degrees exactly.

Gamma-ray astronomy on the ground

It is, however, more recently, possible by means of so -called Cherenkov telescopes to observe gamma rays indirectly from the ground by observing the response of the gamma rays with the Earth's atmosphere. This produces the clash of gamma photons with the atoms in the upper atmosphere Sekundärteilchenschauer, which in turn emit during flight through the atmosphere, so-called Cherenkov light. The resulting direction of flight of the particles ( ie on the ground ) directed conical flash of light can now be measured with Cherenkov telescopes.

History

Even if was suspected as early as the 1940s and 1950s, that there could be gamma rays in space, so you could but only the satellite Explorer 11 (launched on 27 April 1961), which was built just for this purpose, discover gamma rays. During his four months long mission he spotted 22 gamma-ray events.

Gamma satellite

This was the first of a series of satellites that observe regularly from now on in orbit gamma rays:

• OSO -3 gamma-ray sources discovered in 1967 along our galaxy, the Milky Way, which focused around the halo.
• The Vela satellites actually American spy satellites, which should detect nuclear tests, discovered between July 1969 to April 1979 for the first time the so-called gamma-ray bursts.
• SAS -2 ( NASA) and COS -B ( ESA) were able to provide detailed maps of the gamma spectrum in space in the 1970s for the first time.
• CGRO, a 17 -ton satellite superlative, supplied in the 1990s, enormous amounts of data on gamma-ray sources and advanced our knowledge in this area tremendously. However, he had to be launched in 2000 to crash.
• INTEGRAL satellite with an even more accurate resolution, the ESA has placed in orbit on 17 October 2002.
• Fermi Gamma - ray Space Telescope, a wide-angle gamma-ray space telescope (former name Gamma -ray Large Area Space Telescope, GLAST ) was launched into orbit on 11 June 2008.

Gamma telescopes on the ground

Are In the ground-based observation of gamma rays, after a series of smaller pilot projects, to name two pioneering projects that are in operation:

• H.E.S.S. (High Energy Stereoscopic System) in Namibia, which consists of four telescopes with a diameter of 13 meters and features a large telescope with 614 m² mirror surface in the middle of the square array. The levels of the individual telescopes in turn consist of 400 circular (60 cm diameter ) and 875 hexagonal (90 cm edge - to-edge ) segments.
• MAGIC (Major Atmospheric Gamma -ray Imaging Cherenkov Telescope ) on La Palma, Canary Islands. The telescope has a 17 -meter mirror segment consists of 1000 individual aluminum plates and can be used in particular for the observation of short-lived gamma-ray bursts due to its mobility. It is the successor of the HEGRA Atmospheric Cherenkov Telescope System at the same place.

Research objects of gamma-ray astronomy

Due to the above-mentioned high energy gamma rays ( 105 eV compared to light with ~ 1.5 ... 3 eV ) and the formation mechanism of this radiation very different than that of light must be. In the majority of these are dramatic explosions and collisions in space:

• Gamma-ray bursts, which last a few seconds and outshine all other gamma-ray sources in the universe for this time. They are according to the latest theories in most cases a special type of supernova explosion of a massive star at the end of his life.
• Remnants of supernova explosions, such as neutron stars and black holes send the capture of matter also gamma radiation from ( in black holes this radiation is also called the death-cry of the matter, since it is the last thing you see of her)
• Shock waves in the cast-off gas envelopes of stellar explosions that occur when the bounces with almost the speed of light expanding gas to slower gas.
• Hot gas clouds that are stimulated constantly by various processes. For example. intergalactic gas in galaxy clusters.
• Active galaxies. So galaxies in which implemented a lot of energy. These include starburst galaxies (extremely high rate of star formation, especially by galaxy collisions caused ), active galactic nuclei ( the central region and in particular the central black hole are extremely active, ie a quasar )
• Finally, one looks for traces of Annihilation ( pairs annihilation ) of dark matter around this mysterious matter, whose work can be seen through its gravitational effects in the universe indirectly, to be able to demonstrate directly and find out what particles it is made.

The highest ever observe photon energy of 16 TeV observed with the HEGRA telescope, had their source in the Blazar Markarian 501