Information AboutNeutron Stars |
| CATEGORIES ABOUT NEUTRON STAR | |
| neutron stars | |
| neutron | |
| star | |
| star types | |
| exotic matter | |
|
A Neutron star is formed from the Collapsed remnant of a massive star, a Type II , Type Ib , or Type Ic Supernova and models predict that it consists mostly of neutrons. It is a cold star supported by the Pauli Exclusion Principle repulsion between neutrons. A neutron star is one of the few possible Conclusions of Stellar Evolution . A typical neutron star has a Mass between 1.35 And About 2.1 Solar Mass es, with a corresponding Radius between 20 and 10 Km — 30,000 to 70,000 times smaller than the Sun . Thus, neutron stars have densities of 8×1013 To 2×1015 G / Cm³ , about the density of an Atomic Nucleus .1 In general, compact stars of less than 1.44 solar masses, the Chandrasekhar Limit , are White Dwarf s; above 2 to 3 solar masses (the Tolman-Oppenheimer-Volkoff Limit ), a Quark Star might be created, however this is uncertain. Gravitational Collapse will always occur on any star over 5 solar masses, inevitably producing a Black Hole . FORMATION As the core of a massive star is compressed during a supernova, and collapses into a neutron star, it retains most of its Angular Momentum . Since it has only a tiny fraction of its parent's radius (and therefore its Moment Of Inertia is sharply reduced), a neutron star is formed with very high rotation speed, and then gradually slows down. Neutron stars are known to have rotation periods between about 1.4ms to thirty seconds. The neutron star's compactness also gives it very high Surface Gravity , 2×1011 to 3×1012 times stronger than that of Earth . One measure of such immense gravity is the fact that neutron stars have an Escape Velocity of around 150,000 Km/s , about 50psl . Matter falling onto the surface of a neutron star would strike the star also at 150,000km/s , and then be crushed under its own weight into a puddle less than an atom thick. STRUCTURE Current understanding of the structure of neutron stars is defined by existing mathematical models. A neutron star is so dense that one teaspoon of its material would weigh 100 million metric tons. On the basis of current models, the matter at the surface of a neutron star is composed of ordinary Atomic Nuclei as well as Electron s. The "atmosphere" of the star is roughly one meter thick, below which one encounters a solid "crust". Proceeding inward, one encounters nuclei with ever increasing numbers of neutrons; such nuclei would quickly decay on Earth, but are kept stable by tremendous pressures. Proceeding deeper, one comes to a point called Neutron Drip where free neutrons leak out of nuclei. In this region, there are nuclei, free electrons, and free neutrons. The nuclei become smaller and smaller until the core is reached, by definition the point where they disappear altogether. The exact nature of the superdense matter in the core is still not well understood. While this theoretical substance is referred to as Neutronium in Science Fiction and popular literature, the term "neutronium" is rarely used in scientific publications, due to ambiguity over its meaning. The term Neutron-degenerate Matter is sometimes used, though not universally as the term incorporates assumptions about the nature of neutron star core material. Neutron star core material could be a Superfluid mixture of neutrons with a few Proton s and electrons, or it could incorporate high-energy particles like Pion s and Kaon s in addition to neutrons, or it could be composed of Strange Matter incorporating Quark s heavier than Up and Down Quark s, or it could be Quark Matter not bound into Hadron s. (A compact star composed entirely of strange matter would be called a Strange Star .) However so far observations have neither indicated nor ruled out such exotic states of matter. HISTORY OF DISCOVERIES .]] In 1932, Sir James Chadwick discovered the neutron as an elementary particle,2 for which he was awarded the Nobel Prize In Physics in 1935. In 1933, formula ''E'' = ''mc''&2, is 1 solar mass. It is ultimately this energy that powers the supernova. In 1965, Antony Hewish and Samuel Okoye discovered "an unusual source of high radio brightness temperature in the Crab Nebula.4" This source turned out to be the Crab Nebula neutron star that resulted from the great supernova of 1054 CE. In 1967, Jocelyn Bell and Antony Hewish discovered regular radio pulses from the location of the Hewish and Okoye radio source. This Pulsar , was later interpreted as originating from an isolated, rotating neutron star. The energy source of the pulsar is the rotational energy of the neutron star. The largest number of known neutron stars are of this type (See Rotation-powered Pulsar ). In 1971, Riccardo Giacconi , Herbert Gursky, Ed Kellogg, R. Levinson, E. Schreier, and H. Tananbaum discovered 4.8 second pulsations in an X-ray source in the Constellation Centaurus , Cen X-3. They interpreted this as resulting from a rotating hot neutron star. The energy source is gravitational and results from a Rain Of Gas Falling onto the surface of the neutron star from a Companion Star or the Interstellar Medium (See Accretion-powered Pulsar ). In 1974, Antony Hewish was awarded the Nobel Prize In Physics "for his decisive role in the discovery of pulsars" without Samuel Okoye and Jocelyn Bell who shared in the discovery. ROTATION 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 Hundred Times Per Second , distorting into an Oblate Spheroid shape despite their own immense gravity (an Equatorial Bulge ). Over time, neutron stars slow down because their rotating magnetic fields radiate energy; older neutron stars may take several seconds for each revolution. 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. Sometimes a neutron star will ''spin up'' or 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 starquake: As the rotation of the star slows down, the shape becomes more spherical. Due to the stiffness of the 'neutron' crust, this happens as discrete events as the crust ruptures, similar to tectonic earthquakes. After the starquake, the star will have a smaller equatorial radius, and since angular momentum is conserved, rotational speed increases. Neutron stars may "pulse" due to particle acceleration near the Magnetic Pole s, 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 Pulsar s. The most rapidly rotating neutron star currently known, PSR J1748-2446ad, rotates at 716 revolutions per secondhttp://arxiv.org/abs/astro-ph/0601337. A recent paper reported the detection of an X-ray burst oscillation (an indirect measure of spin) at 1122 Hz from the neutron star XTE J1739-285http://www.journals.uchicago.edu/cgi-bin/resolve?id=doi:10.1086/513270. However, at present this signal has only been seen once, and should be regarded as tentative until confirmed in another burst from this star. SUBTYPES
GIANT NUCLEI A neutron star has some of the properties of an Atomic Nucleus , including density, and being made of Nucleon s. In popular scientific writing, neutron stars are therefore sometimes described as giant nuclei. However, in other respects, neutron stars and atomic nuclei are quite different. In particular, a nucleus is held together by the Strong Force , while a neutron star is held together by Gravity . It is generally more useful to consider such objects as Star s. TRIVIA In Carl Sagan 's TV documentary series "Cosmos", Sagan states that a tablespoon of mass from a neutron star is so dense it would weigh as much as a large mountain. If it were dropped on Earth it would travel straight through to the core, out the otherside, then fall back and forth through the earth, destroying much of its center. SEE ALSO
REFERENCES EXTERNAL LINKS
|
|
|