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When in a supernova a star collapses to a neutron star, its magnetic field increases dramatically in strength. Duncan and Thompson calculated that the magnetic field of a neutron star, normally an already enormous 108 tesla could under certain circumstances grow even larger, to more than 1011 tesla. Such a highly magnetic neutron star is called a magnetar.
In the outer layers of a magnetar, which consist of a plasma of heavy elements (mostly iron), tensions can arise that leads to ' starquakes'. These seismic vibrations are extremely energetic, and result in a burst of X-ray and gamma ray radiation. To astronomers, such an object is known as a soft gamma repeater.
It is estimated that about 1 in 10 supernova explosions results in a magnetar rather than a more standard neutron star or pulsar. It only happens when the star already has a fast rotation and strong magnetic field before the supernova. It is thought that a magnetar's magnetic field is created as a result of a convection-driven dynamo of hot nuclear matter in the neutron star's interior that operates in the first ten seconds or so of a neutron star's life. If the neutron star is initially rotating as fast as the period of convection, about ten milliseconds, then the convection currents are able to operate globally and transfer a significant amount of their kinetic energy into magnetic field strength. In slower-rotating neutron stars, the convection currents only form in local regions.
The life of a magnetar as a soft gamma repeater is short: The energy of these explosions slows the rotation (causing magnetars to rotate much more slowly than other neutron stars of a similar age) and weakens the magnetic field, and after only about 10,000 years the starquakes cease. After this, the star still radiates X-rays, forming an object known to astronomers as an anomalous X-ray pulsar (AXP). After another 10,000 years, it becomes completely quiet. At the moment (2000), 4 soft gamma repeaters and 6 anomalous X-ray pulsars are known.
As mentioned previously, magnetars have a magnetic field of above 10 gigatesla, strong enough to wipe a credit card from the distance of the Sun from the Earth and strong enough to be fatal from the distance of the MoonFor other moons in the solar system see natural satellite. For other uses see Moon (disambiguation). The Moon is the only natural satellite of Earth. It has no formal name other than "The Moon" although it is occasionally called Luna ( Latin for moon to d. By comparison, Earth's natural magnetic field is 50 microtesla, and on Earth a fatal magnetic field is only a theoretical possibility; some of the strongest fields generated are actually used in medical imaging. A small neodymiumPraseodymium Neodymium Promethium Nd U Full table General Name, Symbol, NumberNeodymium, Nd, 60 Chemical series Lanthanides Group, Period, Block _, 6 , f Density, Hardness 6800 kg/m3, no data Appearance silvery white, yellowish tinge Atomic properties Ato based rare earthA rare earth is an oxide of a rare earth element. Often rare earth elements themselves are loosely called "rare earths". Rare earth elements, or metals, are the lanthanides and actinides. They come from the f-block. They are: lanthanum, cerium, praseodymi magnet has a field of about a tesla, and most media used for data storage can be erased with millitesla.