Neutron star

:This article is about the celestial body. "Neutron Star" was a 1966 Hugo award winning short story by Larry Niven

Some neutron stars that can be observed

• X-ray burster - a neutron star with a low mass binary companion from which matter is accreted resulting in irregular bursts of energy from the surface of the neutron star.
• Pulsar - general term for neutron stars that emit directed pulses of radiation towards us at regular intervals due to their strong magnetic fields.
• Magnetar - a neutron star with an extremely strong magnetic field; some magnetars are observed as soft gamma repeaters.

Neutron stars rotate extremely rapidly after their creation due to the conservation of angular momentum; like an ice skater pulling in his or her arms, the slow rotation of the original star's core speeds up as it shrinks. A newborn neutron star can rotate several times a second; sometimes, when they orbit a companion star and are able to accrete matter from it, they can increase this to several thousand times per second, distorting into an oblate spheroid shape despite their own immense gravity (an equatorial bulge).

Related Topics:
Oblate spheroid - Equatorial bulge

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Over time, neutron stars slow down because their rotating magnetic fields radiate energy; older neutron stars may take several seconds for each revolution.

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The rate at which a neutron star slows down its rotation is usually constant and very small: the observed rates are between 10-10 and 10-21 second for each rotation. In other words, for a typical slow down rate of 10-15 seconds per rotation, then a neutron star now rotating in 1 second will rotate in 1.000003 seconds after a century, or 1.03 seconds after 1 million years.

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Sometimes a neutron star will undergo a glitch: a rapid and unexpected increase of its rotation speed (of the same, extremely small scale as the constant slowing down). Glitches are thought to be the effect of a sudden coupling between the superfluid interior and the solid crust.

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Neutron stars also have very intense magnetic fields - typically about 1012 times stronger than Earth's. Neutron stars may "pulse" due to particle acceleration near the magnetic poles, which are not aligned with the rotation axis of the star. Through mechanisms not yet entirely understood, these particles produce coherent beams of radio emission. External viewers see these beams as pulses of radiation whenever the magnetic pole sweeps past the line of sight. The pulses come at the same rate as the rotation of the neutron star, and thus, appear periodic. Neutron stars which emit such pulses are called pulsars.

Related Topics:
Magnetic field - Pulsar

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Pulsars

When pulsars were first discovered, the fast time scale of radio pulses (about 1 s, uncommon to astronomy at those days) was

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half-seriously considered to be caused by by extraterrestrial intelligence, later jokingly referred to as LGM-1, for "Little Green Men." The discovery of many pulsars, spread all over the sky with different rotation periods quickly excluded this option.

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The discovery of a pulsar associated with the Vela supernova remnant, soon followed by the further discovery of a pulsar which appeared to be powering the Crab Nebula, produced compelling arguments for the neutron star interpretation.

Related Topics:
Supernova remnant - Crab Nebula

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Magnetars

Another class of neutron star, known as the magnetar, exists. These have a magnetic field of about 100 gigateslas, strong enough to wipe a credit card on Earth from the Moon's orbit. By comparison, the Earth's natural magnetic field is about 60 microteslas. A small neodymium based rare earth magnet has a field of about a tesla, and most media used for data storage can be erased with milliteslas.

Related Topics:
Magnetar - Teslas - Neodymium - Rare earth

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Magnetars occasionally produce bursts of X-ray emission. About once per decade, a magnetar somewhere in the Galaxy produces a giant flare of gamma-rays. Magnetars have long rotation periods, typically 5 to 12 seconds, because their strong magnetic fields have caused them to slow down.

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