Astronomy and Astrophysics – Astrophysics – General Relativity and Quantum Cosmology
Scientific paper
2006-01-06
Mon.Not.Roy.Astron.Soc.Lett. 367 (2006) L66-L68
Astronomy and Astrophysics
Astrophysics
General Relativity and Quantum Cosmology
Small changes at proof stage, shows zero radiation density for collapse implies zero restmass density, MNRAS Letters (in press
Scientific paper
10.1111/j.1745-3933.2006.00141.x
By using elementary astrophysical concepts, we show that for any self-luminous astrophysical object, the ratio of radiation energy density inside the body (rho_r) and the baryonic energy density (rho_0) may be crudely approximated, in the Newtonian limit, as rho_r/rho_0 ~ GM/Rc^2, where G is constant of gravitation, c is the speed of light, M is gravitational mass, and R is the radius of the body. The key idea is that radiation quanta must move out in a diffusive manner rather than free stream inside the body of the star. When one would move to the extreme General Realtivistic case i.e., if the surface gravitational redshift, z >> 1, it is found that, rho_r/rho_0 ~ (1+z). Previous works on gravitational collapse, however, generally assumed rho_r/rho_0 << 1. On the other hand, actually, during continued general relativistic gravitational collapse to the Black Hole state (z --> infty), the collapsing matter may essentially become an extremely hot fireball a la the very early universe even though the observed luminosity of the body as seen by a faraway observer, L^\infty ~ (1+z)^{-1} --> 0 as z --> infty, and the collapse might appear as ``adiabatic''.
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