Give me deep information about neutron star.?

Answer 1

A neutron star is one of the few possible endpoints of stellar evolution. A neutron star is formed from the collapsed remnant of a massive star after a Type II, Type Ib, or Type Ic supernova.

A typical neutron star has a mass between 1.35 to about 2.1 solar masses, with a corresponding radius between 20 and 10 km (they shrink as their mass increases) — 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] Compact stars of less than 1.44 solar masses, the Chandrasekhar limit, are white dwarfs; above three to five solar masses (the Tolman-Oppenheimer-Volkoff limit), gravitational collapse occurs, inevitably producing a black hole.

Since a neutron star retains most of the angular momentum of its parent star but has only a tiny fraction of its parent's radius, the moment of inertia decreases sharply causing a rotational acceleration to a very high rotation speed, with one revolution taking anywhere from one seven-hundredth of a second to thirty seconds. The neutron star's compactness also gives it high surface gravity, 2×1011 to 3×1012 times stronger than that of Earth. One of the measures for the gravity is the escape velocity, the velocity needed for an object to escape from the gravitational field to infinite distance. For a neutron star, such velocities are typically 150,000 km/s, about 1/2 of the velocity of light. Conversely, matter falling onto the surface of a neutron star would strike the star also at 150,000 km/s.

Current understanding of the structure of neutron stars is defined by existing mathematical models, which of course are subject to revision. On the basis of current models, the matter at the surface of a neutron star is composed of ordinary atomic nuclei as well as electrons. 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 that 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 protons and electrons, or it could incorporate high-energy particles like pions and kaons in addition to neutrons, or it could be composed of strange matter incorporating quarks heavier than up and down quarks, or it could be quark matter not bound into hadrons. (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.

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).

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 sudden coupling between the superfluid interior and the solid crust.

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.


Pulsars
When pulsars were first discovered, the fast time scale of pulses (about 1 s, uncommon to astronomy in the 1960s) was half-seriously considered to be caused 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. 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.


Magnetars
Another class of neutron star exists, known as the magnetar. These have a magnetic field of about 100 gigateslas, roughly a thousand times stronger than the fields of normal neutron stars. This is strong enough to erase a credit card on Earth from half the distance of 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.

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 their rotation to slow.


Giant Nuclei?
A neutron star has some of the properties of an atomic nucleus, including density, and being made of nucleons. 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 stars.

Answer 2

Neutron stars are believed to form in supernovae such as the one that formed the Crab Nebula (or check out this cool X-ray image of the nebula, from the Chandra X-ray Observatory). The stars that eventually become neutron stars are thought to start out with about 8 to 20-30 times the mass of our sun. These numbers are probably going to change as supernova simulations become more precise, but it appears that for initial masses much less than 8 solar masses the star becomes a white dwarf, whereas for initial masses a lot higher than 20-30 solar masses you get a black hole instead (this may have happened with Supernova 1987A, although detection of neutrinos in the first few seconds of the supernova suggests that at least initially it was a neutron star). In any case, the basic idea is that when the central part of the star fuses its way to iron, it can't go any farther because at low pressures iron 56 has the highest binding energy per nucleon of any element, so fusion or fission of iron 56 requires an energy input. Thus, the iron core just accumulates until it gets to about 1.4 solar masses (the "Chandrasekhar mass"), at which point the electron degeneracy pressure that had been supporting it against gravity gives up the ghost and collapses inward.
At the very high pressures involved in this collapse, it is energetically favorable to combine protons and electrons to form neutrons plus neutrinos. The neutrinos escape after scattering a bit and helping the supernova happen, and the neutrons settle down to become a neutron star, with neutron degeneracy managing to oppose gravity. Since the supernova rate is around 1 per 30 years, and because most supernovae probably make neutron stars instead of black holes, in the 10 billion year lifetime of the galaxy there have probably been 10^8 to 10^9 neutron stars formed. One other way, maybe, of forming neutron stars is to have a white dwarf accrete enough mass to push over the Chandrasekhar mass, causing a collapse. This is speculative, though, so I won't talk about it further

Answer 3

Neutron stars are the collapsed cores of some massive stars. They pack roughly the mass of our Sun into a region the size of a city.
Neutron stars are believed to form in supernovae such as the one that formed the Crab Nebula.
The stars that eventually become neutron stars are thought to start out with about 8 to 20-30 times the mass of our sun.

http://www.astro.umd.edu/~miller/nstar.html#formation

Answer 4

Neutron stars are believed to form in supernovae such as the one that formed the Crab Nebula (or check out this cool X-ray image of the nebula, from the Chandra X-ray Observatory). The stars that eventually become neutron stars are thought to start out with about 8 to 20-30 times the mass of our sun. These numbers are probably going to change as supernova simulations become more precise, but it appears that for initial masses much less than 8 solar masses the star becomes a white dwarf, whereas for initial masses a lot higher than 20-30 solar masses you get a black hole instead (this may have happened with Supernova 1987A, although detection of neutrinos in the first few seconds of the supernova suggests that at least initially it was a neutron star). In any case, the basic idea is that when the central part of the star fuses its way to iron, it can't go any farther because at low pressures iron 56 has the highest binding energy per nucleon of any element, so fusion or fission of iron 56 requires an energy input. Thus, the iron core just accumulates until it gets to about 1.4 solar masses (the "Chandrasekhar mass"), at which point the electron degeneracy pressure that had been supporting it against gravity gives up the ghost and collapses inward.
At the very high pressures involved in this collapse, it is energetically favorable to combine protons and electrons to form neutrons plus neutrinos. The neutrinos escape after scattering a bit and helping the supernova happen, and the neutrons settle down to become a neutron star, with neutron degeneracy managing to oppose gravity. Since the supernova rate is around 1 per 30 years, and because most supernovae probably make neutron stars instead of black holes, in the 10 billion year lifetime of the galaxy there have probably been 10^8 to 10^9 neutron stars formed. One other way, maybe, of forming neutron stars is to have a white dwarf accrete enough mass to push over the Chandrasekhar mass, causing a collapse. This is speculative, though, so I won't talk about it further.



The guts of a neutron star
We'll talk about neutron star evolution in a bit, but let's say you take your run of the mill mature neutron star, which has recovered from its birth trauma. What is its structure like? First, the typical mass of a neutron star is about 1.4 solar masses, and the radius is probably about 10 km. By the way, the "mass" here is the gravitational mass (i.e., what you'd put into Kepler's laws for a satellite orbiting far away). This is distinct from the baryonic mass, which is what you'd get if you took every particle from a neutron star and weighed it on a distant scale. Because the gravitational redshift of a neutron star is so great, the gravitational mass is about 20% lower than the baryonic mass.
Anyway, imagine starting at the surface of a neutron star and burrowing your way down. The surface gravity is about 10^11 times Earth's, and the magnetic field is about 10^12 Gauss, which is enough to completely mess up atomic structure: for example, the ground state binding energy of hydrogen rises to 160 eV in a 10^12 Gauss field, versus 13.6 eV in no field. In the atmosphere and upper crust, you have lots of nuclei, so it isn't primarily neutrons yet. At the top of the crust, the nuclei are mostly iron 56 and lighter elements, but deeper down the pressure is high enough that the equilibrium atomic weights rise, so you might find Z=40, A=120 elements eventually. At densities of 10^6 g/cm^3 the electrons become degenerate, meaning that electrical and thermal conductivities are huge because the electrons can travel great distances before interacting.

Deeper yet, at a density around 4x10^11 g/cm^3, you reach the "neutron drip" layer. At this layer, it becomes energetically favorable for neutrons to float out of the nuclei and move freely around, so the neutrons "drip" out. Even further down, you mainly have free neutrons, with a 5%-10% sprinkling of protons and electrons. As the density increases, you find what has been dubbed the "pasta-antipasta" sequence. At relatively low (about 10^12 g/cm^3) densities, the nucleons are spread out like meatballs that are relatively far from each other. At higher densities, the nucleons merge to form spaghetti-like strands, and at even higher densities the nucleons look like sheets (such as lasagna). Increasing the density further brings a reversal of the above sequence, where you mainly have nucleons but the holes form (in order of increasing density) anti-lasagna, anti-spaghetti, and anti-meatballs (also called Swiss cheese).

When the density exceeds the nuclear density 2.8x10^14 g/cm^3 by a factor of 2 or 3, really exotic stuff might be able to form, like pion condensates, lambda hyperons, delta isobars, and quark-gluon plasmas.

Answer 5

the quick answer is "neutrons." some stars can attain a undeniable element of their evolution the place their inward rigidity will become so severe that the protons and electrons of its atoms are fused into neutrons.

Answer 6

(1) Most Type II supernovae leave behind an extremely dense neutron star.
Just a reminder: A type II supernova occurs when the iron core of a supergiant star collapses to the density of an atomic nucleus (a few hundred million tons per cubic centimeter). At such tremendously high densities, protons and electrons are fused together into neutrons. The relevant reaction is this:
e- + p -> n + neutrino
About 1057 neutrinos are made in the iron core, as the protons (p) are converted to neutrons (n). The billion trillion trillion trillion trillion neutrinos carry off most of the supernova's energy (photons are just a minor byproduct of a supernova).
After its ``bounce'', the star's core settles down as a sphere of tightly packed neutrons, known as a neutron star. A neutron star can be thought of as a single humongous atomic nucleus (containing roughly 1057 neutrons) with a mass between 1 and 3 solar masses, packed into a sphere 5 to 20 kilometers in radius. To put things into perspective, a neutron star is about as big as the beltway around Columbus.

In addition to being amazingly dense, neutron stars have other amazing properties:

Rapidly rotating: up to 1000 rotations/second, compared to 1 rotation/month for the Sun.
Strongly magnetized: up to 1 trillion Gauss, compared to an average of 1 Gauss for the Sun (and 0.5 Gauss for the Earth).
Very hot: initially 1,000,000 Kelvin at the surface, compared to 5800 Kelvin for the Sun.
The surface of a neutron star is not anyplace you would want to visit. The gravitational acceleration is 100 billion g's (that is, 100 billion times the gravitational acceleration at the Earth's surface). The escape speed at the surface of a neutron star is half the speed of light (that is, 150,000 km/sec, versus a paltry 11 km/sec for the Earth). On the surface of a neutron star, you'd be simultaneously vaporized by the intense heat and squashed flat by the intense gravitational force.
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(2) A neutron star is a compact object supported by degenerate-neutron pressure.
Neutrons, like electrons, must follow the laws of quantum mechanics. In particular, they must obey the Pauli exclusion principle, as outlined in last Thursday's lecture. The existence of neutron stars was actually first predicted in 1933, only a year after the discovery of the neutron.
At a density of 1 ton/cm3, electrons are degenerate, and provide degenerate-electron pressure.

At a density of 400 million tons/cm3, neutrons are finally degenerate, and provide degenerate-neutron pressure.

The interior structure of a neutron star is fairly uncertain. (We don't know a lot about how matter behaves at these amazingly high densities.) One proposed model looks like this:


Just as there is an upper limit on the mass of a white dwarf, there is an upper limit on the mass of a neutron star. White dwarfs can't have M > 1.4 Msun; above this mass, the degenerate-electron pressure is insufficient to prevent collapse. Neutron stars can't have M > 3 Msun; above this mass, the degenerate-neutron pressure is insufficient to prevent collapse (the upper mass limit for neutron stars is fairly uncertain). If a dense object is too massive to be a white dwarf or a neutron star, it's BLACK HOLE TIME (more about black holes next week..)

It's certainly true that the laws of quantum mechanics predict the existence of neutron stars. However, how can we detect them, to verify that they actually exist? Well, neutron stars may be tiny, but they are also hot, and hence produce a significant amount of blackbody radiation.

R = 15 km = 0.00002 Rsun
T = 1,000,000 K = 170 Tsun
Therefore, L = (0.00002)2 (170)4 Lsun = 0.3 Lsun
At a temperature of 1,000,000 Kelvin, the wavelength of maximum emission is at 2.9 nanometers -- in the X-ray range. We can hunt for hot neutron stars by looking for X-ray sources. Although most of the light from neutron stars is emitted at X-ray wavelengths, the nearest neutron star can also be glimpsed at visible wavelengths.
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(3) Rapidly rotating, strongly magnetic neutron stars emit narrow beams of radiation.
Although neutron stars do emit blackbody radiation, they are not simply boring spherical blackbodies, as stars are. Neutron stars have additional ways of emitting electromagnetic radiation. The strong magnetic field and rapid rotation of a neutron star make it a very potent electrical generator. (Here on Earth, commercial electrical generators work by rotating a series of magnets inside a coil of wires. The essential point is that you need to have a magnetic field in motion.) The electric field generated by the rotating magnetized neutron star is strong enough to rip charged particles (such as electrons) away from the surface of the neutron star.
The charged particles follow the magnetic field lines to the north and south magnetic poles of the neutron star. (Remember, when I discussed the magnetic field of the Sun, I pointed out that charged particles move most readily along the magnetic field lines, rather than perpendicular to them.) The accelerated particles produce intense but narrow beams of radiation, pointing away from the two magnetic poles. We can see one of these beams of light ONLY if it is pointing toward us, just as we see the light from a flashlight only when it is pointing toward us.

A complicating factor is that on a neutron star, just as on Earth, the magnetic poles don't coincide with the rotational poles. Thus, the beams of radiation pointing away from the magnetic poles are at an angle to the rotation axis of the neutron star; as the neutron star rotates, the beams swing around in a cone. If a beam happens to sweep across our location in space, we see a brief flash of light. (This is sometimes known as the ``Lighthouse effect''. If you are down by the shore at night, you see lighthouses emit a blinking light. This is not because the lamp in a lighthouse is turned off and on, but because it inside a searchlight which is rotated around and around. As the beam of light from the searchlight sweeps across your location, you see a brief flash of light.)

Answer 7

deep.