Black dwarfs holes

In stars of small mass (<0.1 times the mass of the sun) the energy liberated by gravitational contraction is not sufficient to reach the temperature necessary to start thermonuclear reactions. These stars are directly entering the stage of black dwarfs (black holes). 

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. 

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

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 We must also include matter going into planets and aborted stars (brown dwarfs), forever frozen and permanently withdrawn from the (nuclear) chemical evolution of the Galaxy. 

Schonfelder V. (ed.) (2001) The Universe in Gamma Rays (Springer-Verlag, Berlin). Sexl R. Sexl H. (1979) White Dwarfs - Black Holes An Introduction to Relativistic Astrophysics (Academic Press, New York). 

When we talk about black holes, I ll tell you more about the density of stars. For now, realize that the Sun is actually only slightly more dense than water. Because red giants have about the same mass as the Sun in a huge volume, their average densities are very low—about the same as that of vacuums produced on Earth. On the other hand, consider the white dwarfs. These are faint stars that are the evolutionary endpoints of intermediate- and low-mass stars. A majority of stars, like our Sun, end their lives as white dwarfs. If I were to give you a thimble full of white dwarf mass, you could never lift it. A teaspoon of white dwarf material weighs several tons on Earth. The time needed for a white dwarf to cool down is billions of years. ... 

Yes, Bob says, and beyond that the smallest, longest-lived dwarfs can last 100 billion years, but sooner or later there will be no more new stars. Then all we ll have are the dense black holes, neutron stars, and some white dwarfs. Maybe finally everything will collapse into huge black holes. ... 

Aside from white dwarfs, there is another possible graveyard state for stars. Although it s rarer than a white dwarf, stars between 1.4 and about 5 solar masses can explode to create neutron stars when they die. Neutron stars have radii of only around 10 miles, yet they retain all of the mass of the star s core— at least 1.4 times the full mass of the Sun. A neutron star is formed when the core of a supernova collapses inward and becomes compressed together. Neutrons at the surface of the star decay into protons and electrons. Stars with masses greater than about 5 solar masses will become black holes 6... 

Bob continues. White dwarfs maintain the strongest resistance against gravity, black holes the weakest, neutron stars somewhere in between. An extraordinary material called neutronium form neutron stars. Neutronium is so dense that a chunk the size of a thimble would weigh about 100 million tons. This means that a cubic centimeter of neutronium, the size of a sugar cube, has the mass of 100 billion elephants. The Sim, if squashed into a neutron star, would be only a few miles across, the earth just a few inches. The density of neutronium is 1014 times greater than ordinary solid matter. ... 

The quantity AE/A rises from He to Fe, and it declines thereafter (Fig. 2.3) this explains why successive gravitational collapses of dying stars form first He stars, then C stars, then Ne stars, then finally Fe stars. When all nuclear fuel is depleted in an Fe star, an ultimate gravitational collapse into black holes must occur, if the star mass exceeds 8 solar masses, that is, > 1.6 x 1031 kg otherwise the star will decay into a white dwarf. 

The fountain appears to primarily contain positrons, rather than more massive antimatter particles or atoms. Positrons can be created by heated gas spiraling into a black hole, or by the explosions of supernovas and white dwarf stars, leading astronomers to speculate that the fountain is caused by massive star formation near the black hole at the Milky Way s center, or the explosion of young massive stars. 

Baryonic candidates were traditionally brown dwarfs, old white dwarfs, neutron stars, and stellar mass black holes. Both they and the new ones are subject to the big bang nucleosynthesis constraint above others might accrete matter, thus radiating, absorb at some wavelengths, or otherwise reveal themselves. 

BLACK hole NEUTRON STAR WHITE DWARF. 

Shapiro, S.L. and Teukolsky, S.A., Black Holes, White Dwarfs and Neutron Stars, Wiley Interscience, New York, 1983, pp 241-66. 

The physics of the remaining compact objects after stellar death, e.g., white dwarfs, neutron stars, and black holes are discussed by Shapiro and Teukolsky (1983). 

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