http://www.youtube.com/watch?v=rE-U5e78WHc&feature=related
http://www.youtube.com/watch?v=QCQTr8ZYdhg
http://www.youtube.com/watch?v=xOf4SktPDak&feature=related
globular clusters
http://arxiv.org/PS_cache/astro-ph/pdf/0107/0107401v1.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0006/0006314v1.pdf
http://migall.fastmail.fm/astronomy/galaxies/milkyway/milkyway_globulars/page02.htm
http://www.youtube.com/watch?v=DQlgcjosN9w&feature=related
http://www.youtube.com/watch?v=pXSmCdfHudk&feature=related
http://www.youtube.com/watch?v=wuSAeps8vKo&feature=related
http://www.youtube.com/watch?v=MlC-bAb7d6o
http://www.youtube.com/watch?v=wdoobRyL5ck
http://www.youtube.com/watch?v=2IKkOlutKxk&feature=related
http://www.youtube.com/watch?v=wcM4ok1YzBs&feature=related
http://www.youtube.com/watch?v=khySM1YBQvA&feature=related
http://www.youtube.com/watch?v=VVGb7JU4TSU&feature=rellist&playnext=1&list=PL2B2D34DB61757F39
Milky Way Globular Clusters
http://arxiv.org/PS_cache/arxiv/pdf/0711/0711.4795v1.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0703/0703767v1.pdf
Globular clusters are generally composed of hundreds of thousands of low-metal, old stars. The type of stars found in a globular cluster are similar to those in the bulge of a spiral galaxy but confined to a volume of only a few million cubic parsecs. They are free of gas and dust and it is presumed that all of the gas and dust was long ago turned into stars.
http://arxiv.org/PS_cache/astro-ph/pdf/9605/9605141v1.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0406/0406002v1.pdf
NGC 346 is an open cluster..It is located in the Small Magellanic Cloud wich appears in the constellation Tucana.
http://www.bibliotecapleyades.net/universo/open_cluster.htm
47 Tucanae (NGC 104)
This cluster is also located in Tucanae .47 Tuc has 23 known millisecond pulsars, the second largest population of pulsars in any globular cluster. This youngest millisecond pulsar was found by Nasa's Fermi
PSR J1719-1438
http://www.jb.man.ac.uk/research/pulsar/
http://www.eso.org/public/images/eso0620a/
Messier 7( or М7) is also designated as NGC 6475 and sometimes is known as the Ptolemy Cluster . It is an open cluster of stars
M55: Globular Star Cluster
This globular star cluster is also known as M55 (or NGC 6809) It is a globular cluster in the constellation Sagittarius.It is at a distance of about 17,300 light-years away from Earth. Only about half a dozen variable stars have been discovered in M55.
The term compact star (sometimes compact object) is used to refer collectively to white dwarfs, neutron stars, other exotic dense stars, and black holes. These objects are all small for their mass.Compact stars form the endpoint of stellar evolution. A star shines and thus loses energy. The loss from the radiating surface is compensated by the production of energy from nuclear fusion in the interior of the star. When a star has exhausted all its energy and undergoes stellar death, the gas pressure of the hot interior can no longer support the weight of the star and the star collapses to a denser state: a compact star. Below we present two types of compact stars: the (brown and white) dwarf stars and the neutron stars. In the meantime, let's talk about the Chandrasekhar limit .Compact stars form the endpoint of stellar evolution. A star shines and thus loses energy. The loss from the radiating surface is compensated by the production of energy from nuclear fusion in the interior of the star. When a star has exhausted all its energy and undergoes stellar death, the gas pressure of the hot interior can no longer support the weight of the star and the star collapses to a denser state: a compact star. Below we present two types of compact stars: the (brown and white) dwarf stars and the neutron stars. In the meantime, let's talk about the Chandrasekhar limit .When a star starts running out of fuel, it usually cools off and collapses (possibly with a supernova) into one of three compact forms, depending on its total mass: There are a white dwarf,a neutron star, and a black hole .The Chandrasekhar limit is the maximum mass of a stable white dwarf star. The Chandrasekhar limit is analogous to the Tolman/Oppenheimer/Volkoff limit(TOV limit) for neutron stars.The currently accepted numerical value of the limit is about 1.5M0 .Radius/mass relations for a model white dwarf.
NASA - White Dwarf Stars
http://www.nasa.gov/multimedia/imagegallery/image_feature_734.html
. Solving the hydrostatic equation leads to a model white dwarf wich is a polytrope of index 3/2 and therefore has radius inversely proportional to the cube root of its mass, and volume inversely proportional to its mass.As the mass of a model white dwarf increases, the typical energies to wich degeneracy pressure forces the electrons are no longer negligible relative to their rest masses. The velocities of the electrons approach the speed of light, and special relativity must be taken into account. In the strongly relativistic limit, we find that the equation of state takes the form: P=K2ρ4/3.This will yield a polytrope of index 3, that will have a total mass, Mlimit say, depending only on K2.For a fully relativistic treatment, the equation of state used will interpolate between the equations:P=K1ρ5/3the equation of state used will interpolate between the equations for small ρ and P=K2ρ4/3for large ρ. When this is done, the model radius still decreases with mass, but becomes zero at Mlimit. This is the Chandrasekhar limit .The curves of radius against mass for the non-relativistic and relativistic models are shown in the picture №1. They are colored blue and green, respectively. μe has been set equal to 2. Radius is measured in standard solar radii, and mass in standard solar masses.:
This picture№1 shows the radius / mass relations for a model white dwarf
There is black line wich marks the ultra-relativistic limit.The green curve uses the general pressure law for an ideal Fermi gas, and the blue curve is for a non-relativistic ideal Fermi gas.
The values for the limit will vary depending on the nuclear composition of the mass.There is the following expression, wich is based on the equation of state for an ideal Fermi gas:
M lim=(ω03√3п/2)(hc/G)3/2 (1/(μemн)2).ω03 is a constant connected with the solution to the Lane-Emden equation[ The Lane–Emden equation is Poisson's equation for the gravitational potential of a self-gravitating, spherically symmetric polytropic fluid. Without any details , this is an equation whose solution provides the run of pressure and density with radius r in terms of a re-scaled radial variable and a re-scaled density variable].. μe is the average molecular weight per electron, which depends upon the chemical composition of the star.mH is the mass of the hydrogen atom. The Planck constant, the speed of light and the gravitational constant are also counted in this equation (h, h, G).√hc/G is the Planck mass, the limit is of the order of M3pl/m2н.A more exact value of the limit than that given by this simple model requires adjusting for various factors, for example electrostatic interactions between the electrons and nuclei and effects caused by nonzero temperature.[ Yau and Lieb have given a rigorous derivation of the limit from a relativistic many-particle Schrödinger equation].Look at here:
http://articles.adsabs.harvard.edu/full/1987ApJ...323..140L
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1986Ap%26SS.126..357H&data_type=PDF_HIGH&whole_paper=YES&type=PRINTER&filetype=.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0409/0409447v1.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0612/0612312v1.pdf
NGC 2168 (M35).
Messier 35 is also known as M 35 (or NGC 2168). It is an open cluster in the constellation Gemini.
The stars called degenerate dwarfs or, more usually, white dwarfs are made up mainly of degenerate matter-typically, carbon and oxygen nuclei in a sea of degenerate electrons. White dwarfs arise from the cores of main-sequence stars and are therefore very hot when they are formed. As they cool they will redden and dim until they eventually become dark dwarfs.
White Dwarf Stars
http://paradise7.hubpages.com/hub/White-Dwarf
Brown Dwarf Stars
http://www.astronet.ru/db/xware/msg/1162267/m55_mochejska_big.jpg.html
Brown dwarfs are sub-stellar objects that are too low in mass to sustain hydrogen-1 fusion reactions in their cores,and wich is characteristic of stars on the main sequence. These stars have fully convective surfaces and interiors, with no chemical differentiation by depth..
http://arxiv.org/ftp/astro-ph/papers/0608/0608417.pdf
http://arxiv.org/PS_cache/arxiv/pdf/1004/1004.1436v1.pdf
http://arxiv.org/PS_cache/arxiv/pdf/1008/1008.5150v2.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0607/0607305v1.pdf
http://www.impactlab.net/2008/12/05/brown-dwarfs-form-like-stars/
http://arxiv.org/PS_cache/astro-ph/pdf/0607/0607305v1.pdf
http://arxiv.org/PS_cache/arxiv/pdf/1103/1103.0014v3.pdf
http://www.esa.int/esaCP/SEM9E91YUFF_index_0.html
http://news.nationalgeographic.com/news/2006/03/0323_060323_brown_dwarf.html
An artist's impression of a carbon-rich white dwarf
Birth of a White Dwarf Star
http://www.nasa.gov/centers/goddard/news/topstory/2004/0220stardisk.html
http://www.thelivingmoon.com/46jkrog08/02files/Neutron_Stars_Pulsars_and_Magnetars.html
Neutron Stars, Pulsars, and Magnetars
http://arxiv.org/PS_cache/astro-ph/pdf/0405/0405262v1.pdf
An artist's rendering of a magnetar
The first recorded bursts believed to come from a magnetar was observed in the late seventies of last century. The primary theory of magnetar operation was presented in the early nineties of last century by R. Duncan and C. Thompson to explain this and other observed phenomena.Trite, that magnetars are primarily characterized by their extremely powerful magnetic field .And of course , these magnetic fields are hundreds of millions of times stronger than any man-made magnet and also quadrillions of times more powerful than the field surrounding Earth .It can often reach the order of ten gigateslas ... It is uncertain how magnetars are formed, but there is speculation that this may be approximately so:hmm,at first let us show u how to born a normal neutron star,now then :when, in a supernova, a star collapses to a neutron star, its magnetic field increases dramatically in strength. Halving a linear dimension increases the magnetic field fourfold.Well, normal neutron stars are created when a massive star runs out of hydrogen fuel to burn in its core. A cascade of events occur wich eventually causes the outer envelope of the star to explode in a brilliant supernova, leaving behind the neutron core. And during this process the magnetic field of the star is increased due to a physics principle known as flux conservation. And as mentioned, the collapse of the star into a more compact region causes the magnetic field strength to increase in order to maintain a constant field strength far away from the star. However, in the case of magnetars, the conditions of the collapse are somewhat different: - the specific combination of spin, temperature and magnetic field strength conspire to convert some of the stars heat and rotational energy into additional field energy. This energy manifests itself as a stronger magnetic field.. According to the calculations when the spin, temperature and magnetic field of a newly formed neutron star falls into the right ranges, a dynamo mechanism could act, converting heat and rotational energy into magnetic energy, and increasing the magnetic field, normally an already enormous 1012 gauss( or1012teslas)to more than 1011 teslas( or 1015 gauss).Thus, to paraphrase, 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.According to estimates about 1 in 10 supernova explosions results in a magnetar rather than a more standard neutron star or pulsar. .So, to put it more simple terms it only happens when the star already has a fast rotation and strong magnetic field before the supernova.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 lessens the electric field, and after only about 10,000 years the starquakes are over. After this, the star still radiates X-rays, forming an object known to astronomers as an anomalous X-ray pulsar (AXP). .
http://www.cita.utoronto.ca/~thompson/magnetar.pdf
http://www.mssl.ucl.ac.uk/~rs1/msfc/magnetar_draft.pdf
http://www.if.ufrgs.br/hadrons/allen.pdf.
http://arxiv.org/PS_cache/astro-ph/pdf/0306/0306213v4.pdf
Neutron Stars
There are compact stars : And if they are of less than 1.4solar masses then this is the Chandrasekhar limit –, and they are white dwarfs, and above 2 to 3 solar masses (the TOV limit), it might be a quark star ; however, this is uncertain. Gravitational collapse will usually occur on any compact star between 10 and 25 solar masses and produce a black hole(Stellar black holes in close binary systems are observable when matter is transferred from a companion star to the black hole. The energy release in the fall toward the compact star is so large that the matter heats up to temperatures of several hundred million degrees and radiates in X-rays (X-ray astronomy).).
http://maxinewspress.com/black-hole-caught-eating-a-star-gamma-ray-flash-hints.html
This is the most famous stellar mass black hole
http://apod.nasa.gov/apod/ap080811.html
Well, let's say at least two words about the black holes. Gravitational collapse .Well firstly a word or two about gravitational collapse will not be superfluous . What is it? Gravitational collapse is the inward fall of a body due to the influence of its own gravity. In any stable body, this gravitational force is counterbalanced by the internal pressure of the body, in the opposite direction to the force of gravity (gravity being generally orientated to the center of mass).Well, if one is not talking about black holes, this happens until the internal pressure increases above that of the gravitational force and a equilibrium is once again attained .Because gravity is comparatively weak compared to other fundamental forces, gravitational collapse is usually associated with very massive bodies .If the mass of the remnant exceeds about 3 or4 solar masses (the TOV limit) either because the original star was very heavy or because the remnant collected additional mass through accretion of matter / even the degeneracy pressure of neutrons is insufficient to stop the collapse. No known mechanism (for example a quark star) is powerful enough to stop the implosion and the object will inevitably collapse to form a black hole. Frankly it is not yet clear that can the gravitational collapse be complete or not?. We are seeing today the precursor of black holes, or rather black hole candidates, ie these gravitating objects have not yet completed their formation and they are not still black holes in the full sense of the word. Although the behavior of matter around them is identical to that predicted in general relativity.Okay, go on:The gravitational collapse of heavy stars is assumed to be responsible for the formation of stellar mass black holes.Now therefore, according to the no-hair theorem, a black hole can only have three fundamental properties: mass, electric charge and angular momentum (spin). It is believed that black holes formed in nature all have spin, but no definite observation on the spin have been performed. The spin of a stellar black hole is due to the conservation of angular momentum of the star wich is produced it.Well, one can say that: the collapse of a star is a natural process wich can produce a black hole. It is believed that this is inevitable for the end of the life of a star, when all stellar energy sources are exhausted. If the mass of the collapsing part of the star is below a certain critical value, the end product is a compact star, either a white dwarf or a neutron star. Both these stars have a maximum mass. So if the collapsing star has a mass exceeding this limit, the collapse will continue forever (catastrophic gravitational collapse) and form a black hole.It is still not certain maximum weight at wich the possible formation of a black hole. Well, the limit can be different. For example, the maximum mass of a neutron star is not well known, at the end of the thirties ( ie during "the time of Oppenheimer and Teller") it was estimated at 0.7 solar masses, called the TOV limit. In the late nineties of the twentieth century a different estimate put this upper mass in a ranged from 1.5 to 3 solar masses.The largest known stellar black hole is 15.7 ± 1.5 solar masses. In the theory of general relativity, a black hole could exist of any mass. The lower the mass, the higher the density of matter has to be in order to form a black hole. There are no known processes that can produce black holes with mass less than a few times the mass of the Sun.And while this confirmation has not been refuted. .
..In this case, the picture shows only one of the hypotheses.The fact is in that; the quark - gluon plasma is not formed at the cold compression of matter. But the exact information of about the state of matter in the inner layer of objects such as neutron stars and black holes does not exist.. http://www.abovetopsecret.com/forum/thread617225/pg1
We've already talked about white dwarfs. And now we'll talk about the family of neutron stars . .
http://www.daf.on.br/jlkm/astron2e/AT_MEDIA/CH22/CHAP22AT.HTM
http://chandra.harvard.edu/photo/2009/cassio The structure of a tipical neutron star:
Well, actually, let's say the following:- the exact nature of the superdense matter in the core is still not well understood. 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.
http://www.dailygalaxy.com/my_weblog/astronomy/page/50/
http://meditationandspiritualgrowth.com/?m=201008&paged=2
A typical neutron star has a mass between 1.4 and about 2 solar masses with a radius of about 10 km . 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.
http://zebu.uoregon.edu/~soper/NeutronStars/neutronstars.html
Neutron stars are known to have rotation periods between about 1.4 ms to 30 s .
The neutron star's density also gives it very high surface gravity.
the TOV equation:
[eq I]
dP(r)/dr=-(G/r2)[(ρ(r)+(P(r)/c2))][M(r)+4пr3(P(r)/c2)]/[1-(2GM(r)/c2(r)]
http://www.mpa-garching.mpg.de/rel_hydro/effective_relativistic_potential/index.shtml
the Tolman–Oppenheimer–Volkoff (TOV) equation constrains the structure of a spherically symmetric body of isotropic material wich is in static gravitational equilibrium, as modelled by general relativity.The equation is derived by solving the Einstein equations for a general time-invariant, spherically symmetric metric. For a solution to the Tolman / Oppenheimer / Volkoff equation, this metric will have the such form:
ds2=ev(r)c2dt2- dr/(1-GM(r)/rc2)dr2-r2(dΘ2+sin2Θφ),
Where ν(r) is determined by the constraint:dv(r)/dr=-(2/(P(r)+ρ(r)c2))(dP(r)/d(r)).When supplemented with an equation of state, F(ρ, P) = 0, that relates density to pressure, the TOV/equation completely determines the structure of a spherically symmetric body of isotropic material in equilibrium.When supplemented with an equation of state, F(ρ, P) = 0, that relates density to pressure, the TOV/equation completely determines the structure of a spherically symmetric body of isotropic material in equilibrium.This our equation becomes the Newtonian hydrostatic equation , if terms of order 1/c2 are neglected .If the equation is used to model a bounded sphere of material in a vacuum, the zero-pressure condition P(r) = 0 and the condition exp[ν(r)] = 1 − 2GM(r)/rc2 should be imposed at the boundary. The second boundary condition is imposed so that the metric at the boundary is continuous with the unique static spherically symmetric solution to the vacuum field equations , the Schwarzschild metric:
ds2 =(1-2GM0/rc2 )c2 dt2 -(1/(1-2GM0/rc2 )dr2 -r2 (d Θ2 +sin2 d Θ φ2 ).The difference between black holes and neutron stars lies in the next, neutron stars may have additional properties. They show differential rotation, and can have a magnetic field and exhibit localized explosions (thermonuclear bursts). Whenever such properties are observed, the compact object in the binary system is revealed as a neutron star. The derived masses come from observations of compact X-ray sources (combining X-ray and optical data). All identified neutron stars have a mass below 3 to 5 solar masses. None of the compact systems with a mass above 5 solar masses reveals the properties of a neutron star. Thus, the combination of these facts make it more and more likely that the class of compact stars with a mass above 5 solar masses are in fact black hole candidates.In other words, black hole candidates are all objects whose mass is given( ie, although in this limit 3 to 5 solar masses), and whose radius is equal to the Schwarzschild.Let us return to the neutron stars.
http://www.physics.cz/webdata/text/dizertace_urbanec.pdf
http://www.rcnp.osaka-u.ac.jp/~chiral07/files/14pm_room1/Chiral07_takano.pdf
the Akmal-Pandharipande-Ravenhall equation of state (APR EOS)can be obtained can be obtained from the TOV . I will not go into details, I'll just say that one can do it like this: 1) one should use the TOV equation( or hydrostatic equlibrium and mass conservation in GR)[eq I],(2) one should add a prescription for the relation between the pressure and density :P=P(ρ). 3)After that one should intergrate from P(r=0)=Pc to P=0 , wich defines M and R . For each prescription P=P(ρ), this yields a family of solutions as function of initial condition:P=Pc. The relation between P=P(ρ) ( or the so-called EoS( the Equation of State of nuclear matter)) is set by the interactions between the particles wich constituete the star , and can therefore be mapped into a mass-radius relation M=M(R) . The APR EOS opens the powerfull direct Urca proccess of neutrino emission in the interior of most massive neutron stars .
http://arxiv.org/PS_cache/arxiv/pdf/1012/1012.3208v1.pdf
http://www.astro.lsa.umich.edu/~ognedin/papers/mnras363_555_2005.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0507/0507560v1.pdf
http://arxiv.org/PS_cache/astro-ph/pdf/0507/0507560v1.pdf
http://universe-review.ca/R13-10-NSeqs.htm
http://arxiv.org/PS_cache/arxiv/pdf/1011/1011.4291v1.pdf
http://ircamera.as.arizona.edu/NatSci102/NatSci102/lectures/whitedwrf.htm.
Magnetars
http://www.nasa.gov/centers/goddard/news/topstory/2004/0220stardisk_prt.htm
.