THE SUPERNOVA

Observation history

Main article: History of supernova observation

The Crab Nebula is a pulsar wind nebula associated with the 1054 supernova

Hipparchus' interest in the fixed stars may have been inspired by the observation of a supernova (according to Pliny) The earliest recorded supernova, SN 185, was viewed by Chinese astronomers in 185 AD. The brightest recorded supernova was the SN 1006, which was described in detail by Chinese and Islamic astronomers.^[11] The widely observed supernova SN 1054 produced the Crab Nebula. Supernovae SN 1572 and SN 1604, the latest to be observed with the naked eye in the Milky Way galaxy, had notable effects on the development of astronomy in Europe because they were used to argue against the Aristotelian idea that the universe beyond the Moon and planets was immutable.^[12] Johannes Kepler began observing SN 1604 on October 17, 1604.^[13] It was the second supernova to be observed in a generation (after SN 1572 seen by Tycho Brahe in Cassiopeia).

Since the development of the telescope, the field of supernova discovery has extended to other galaxies, starting with the 1885 observation of supernova S Andromedae in the Andromeda galaxy. American astronomers Rudolph Minkowski and Fritz Zwicky developed the modern supernova classification scheme beginning in 1941 In the 1960s, astronomers found that the maximum intensities of supernova explosions could be used as standard candles, hence indicators of astronomical distances. Some of the most distant supernovae recently observed appeared dimmer than expected. This supports the view that the expansion of the universe is accelerating.^[16][17] Techniques were developed for reconstructing supernova explosions that have no written records of being observed. The date of the Cassiopeia A supernova event was determined from light echoes off nebulae,^[18] while the age of supernova remnant RX J0852.0-4622 was estimated from temperature measurements and the gamma ray emissions from the decay of titanium-44.^[20] In 2009, nitrates were discovered in Antarctic ice deposits that matched the times of past supernova events VIA WIKIPEDIA

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THE GAMMA RAY

This article is about the term's use in physics. For other uses, see Gamma ray (disambiguation).

Illustration of an emission of a gamma ray (γ) from an atomic nucleus.

Gamma rays are emitted during radioactive decay processes such as those found in nuclear explosions.

Gamma radiation, also known as gamma rays, and denoted by the Latin letter γ, refers to electromagnetic radiation of extremely high frequency and therefore high energy per photon. Gamma rays are ionizing radiation, and are thus biologically hazardous. They are classically produced by the decay from high energy states of atomic nuclei (gamma decay), but are also created by other processes. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900, while studying radiation emitted from radium. Villard's radiation was named "gamma rays" by Ernest Rutherford in 1903.

Natural sources of gamma rays on Earth include gamma decay from naturally occurring radioisotopes, and secondary radiation from atmospheric interactions with cosmic ray particles. Rare terrestrial natural sources produce gamma rays that are not of a nuclear origin, such as lightning strikes and terrestrial gamma-ray flashes. The electron avalanche builds up quickly, generating more and more high energy particles, in an ever increasing feedback loop, eventually generating a terrestrial gamma ray flash.^[1] Gamma rays are produced by a number of astronomical processes in which very high-energy electrons are produced, that in turn cause secondary gamma rays by the mechanisms of bremsstrahlung, inverse Compton scattering and synchrotron radiation. A large fraction of such astronomical gamma rays are screened by Earth's atmosphere and can only be detected by spacecraft.

Gamma rays typically have frequencies above 10 exahertz (or >10¹⁹ Hz), and therefore have energies above 100 keV and wavelengths less than 10 picometers (less than the diameter of an atom). However, this is not a hard and fast definition, but rather only a rule-of-thumb description for natural processes. Gamma rays from radioactive decay are defined as gamma rays no matter what their energy, so that there is no lower limit to gamma energy derived from radioactive decay. Gamma decay commonly produces energies of a few hundred keV, and almost always less than 10 MeV. In astronomy, gamma rays are defined by their energy, and no production process need be specified. The energies of gamma rays from astronomical sources range over 10 TeV, at a level far too large to result from radioactive decay. A notable example is extremely powerful bursts of high-energy radiation normally referred to as long duration gamma-ray bursts, which produce gamma rays by a mechanism not compatible with radioactive decay. These bursts of gamma rays, thought to be due to the collapse of stars called hypernovae, are the most powerful events so far discovered in the cosmos via wikipedia

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