Black neutron stars

The density of solid materials on earth ranges from about 1 g/cm to 22.5 g/cm (osmium metal). In the interior of certain stars, the density of matter is truly staggering. Black neutron stars—stars composed of neutrons, or atomic cores compressed by gravity to a superdense state—have densities of about 10 g/cm ... 

Coalescing neutron star binaries. Coalescing of neutron stars (or black holes) is foreseen to be the the most powerful source of detectable gw. The frequency of such events is estimated to be ly D/200 Mpc) and their amplitude will allow detection of sources as far as 50 Mpc. We are thus waiting for about one event every 60 years with the current sensitivity of detectors. 

Black holes. One great achievement of gravitational wave astronomy would be the first detection of a signal coming directly from a black hole. Just like with neutron stars, black holes can emit gw either alone or in binary systems. 

Coalescence of black holes. The coalescence of two black holes will generate even more gravitational waves than neutron stars coalescence, and coalescence of two lOM black holes will be detectable up to 500 Mpc... 

This is an extremely small quantity, which combined with the also extremely small interaction of gravitational waves (GWs) with matter makes it impossible to generate and detect GW on earth. Fast conversions of solar-size masses are required to produce signals with amplitudes that could be detectable. Astrophysical sources are for instance supernova explosions or a collision of two neutron stars or black holes. 

Low (<1 solar mass) Middle (5-10 solar masses) High (>20 solar masses) Protostar — pre-main sequence — main sequence — red giant — planetary nebula — white dwarf — black dwarf Protostar - main sequence — red giant — planetary nebula or supernova —> white dwarf or neutron star Protostar — main sequence —> supergiant — supernova — neutron star... 

The result of all these processes is that the Sun was bom 4.6 Gyr ago with mass fractions X 0.70, Y 0.28, Z 0.02. These abundances (with perhaps a slightly lower value of Z) are also characteristic of the local ISM and young stars. The material in the solar neighbourhood is about 15 per cent gas (including dust which is about 1 per cent by mass of the gas) and about 85 per cent stars or compact remnants thereof these are white dwarfs (mainly), neutron stars and black holes. 

Abstract After some historical remarks we discuss different criteria of dynamical stability of stars and the properties of the critical states where the loss of dynamical stability leads to a collapse with formation of a neutron star or a black hole. At the end some observational and theoretical problems related to quark stars are discussed. 

In this review I first make a historical excursus into the problem, mentioning the results of the key works. Several criteria of stability are discussed, with the main focus on the static criteria, and the energetic method, which permits to obtain conclusions about the stability (sometimes approximate) in a most simple way. Critical states of compact stars at the boundary of the dynamic stability are considered, at which the star is becoming unstable in the process of energy losses, and a collapse begins leading to formation of a neutron star or a black hole. Physical processes leading to a loss of stability are discussed. At the end some observations and theoretical problems connected with quark stars are considered. 

The interaction of mass transfer, gravitational wave backreaction and the reaction of the neutron star radius to the mass loss leads to a very complicated accretion dynamics in a neutron star black hole system. We find in all of our simulations (apart from an extreme test case with mass ratio q = 0.93, i.e. a... 

Shapiro, S.L. Teukolsky, S.A. 1983, Black holes, white dwarfs and neutron stars, Ed. J. Wiley Sons. 

A continuous flow of data falls from the sky like a fountain, into the open mouths of satellites like FUSE, Chandra and XMM. An enigmatic portrait of cosmic violence is being painted in our understanding of nature, peopled by supernovas, neutron stars, black holes and stellar corpses, telling of death and the life beyond it. For the panchromatic astronomy of the invisible, the sky is literally exploding upon our understanding. 

Fig. 5.4. Schematic evolution of the internal structure of a star with 25 times the mass of the Sun. The figure shows the various combustion phases (shaded) and their main products. Between two combustion phases, the stellar core contracts and the central temperature rises. Combustion phases grow ever shorter. Before the explosion, the star has assumed a shell-like structure. The centre is occupied by iron and the outer layer by hydrogen, whilst intermediate elements are located between them. CoUapse followed by rebound from the core generates a shock wave that reignites nuclear reactions in the depths and propels the layers it traverses out into space. The collapsed core cools by neutrino emission to become a neutron star or even a black hole. Most of the gravitational energy liberated by implosion of the core (some 10 erg) is released in about 10 seconds in the form of neutrinos. (Courtesy of Marcel Amould, Universite Libre, Brussels.)...

However, according to Stan Woosley, there must be a whole range of masses in which a black hole is not immediately created, but only when a shock wave has blown the star apart. One would feel sure that the explosion had succeeded, and yet a certain fraction of the matter would fall back into the core, for it would have insufficient kinetic energy to resist the call of gravity from the central neutron star. The latter would be transformed into a black hole by the extra matter. This delayed delivery of a black hole may be much more common than the hasty birth described above. 

Up to now, the search for an astrophysical site that could sustain the r process has not brought much success, but it is certainly not for want of imagination. Mergers between two neutron stars or a neutron star and a black hole have even appeared on the list. Notwithstanding, the favourite potential site remains the supernova. However, despite a long inquiry into the matter, we are still unable to put forward a detailed mechanism to show how it would operate. Calculations with the r process in explosive conditions are notoriously difficult, but they are being pursued with courage and determination. 

But all this cannot happen without losses along the way. Stellar corpses and collapsed cores (white dwarfs, neutron stars and black holes) are permanently removed from the great flow of nuclear evolution. It is as though their substance has been conflscated, so that it can no longer take part in the ebb and flow of matter, entering the stars in one form and re-emerging in another. Almost all elements required for life are now present. 

Concerning gas losses, we must subtract gas transformed into stars and the matter imprisoned in stellar corpses. The latter occur in three forms white dwarfs, neutron stars and black holes. We must also include matter going into planets and aborted stars (brown dwarfs), forever frozen and permanently withdrawn from the (nuclear) chemical evolution of the Galaxy. 

Where will humans be, five billion years from now, at the end of the world Even if we could somehow withstand the incredible heat of the sun, we would not survive. In about seven billion years, the Sun s outer atmosphere will engulf the Earth. Due to atmospheric friction, the Earth will spiral into the sun and incinerate. In one trillion years, stars will cease to form and all large stars will have become neutron stars or black holes. In 100 trillion years, even the longest-lived stars will have used up all their fuel. 

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