64 research outputs found
A generic relation between baryonic and radiative energy densities of stars
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''.Comment: Small changes at proof stage, shows zero radiation density for
collapse implies zero restmass density, MNRAS Letters (in press
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