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3

Or does gravity depend on the density of the object as well? The problem with this question is that it's rather ambiguous as to what you mean by "gravity". An object doesn't have a single number that is its "gravity". If a ship is near a star, the gravitational force that the ship feels depends on the mass of the star, the mass of the ...


17

The true answer lies in General Relativity, but we can make a simple Newtonian argument. From the outside, a uniform sphere attracts test masses exactly as if all of its mass was concentrated in the center (part of the famous Shell theorem). Gravitational attraction also increases the closer you are to the source of gravitation, but if you go inside the ...


6

Stars generate a great deal of energy through fusion at the core. Basically the more massive a star is, the more pressure the core is under (due to the star's own gravity) and the more energy it can generate (somewhat simplified). That energy of course radiates outward and heats everything outside the core making it a something like a pressure cooker, with ...


1

If the visible matter became enough dense to be concentrated inside its Schwarzschild radius, it becomes a BH. Until their inner pressure withstand the gravitation they stay being stars.


1

Roughly speaking, for a star to become a black hole, its physical radius has to become smaller than its Schwarzschild radius. So even the Earth could be a black hole if it shrinks to below 9 milimiters. It is not precise to say that a black hole depends on the density of the object, since a Schwarzschild metric is a vacuum solution of Einstein's field ...


0

There is no random walk. Such a photon immediately is aborbed by the 15 million degree plasma. The resulting heat diffuses out over a long period. Finally it appears in the photosphere and where thermal radiation manages to escape and keep us warm.


34

The light from the Sun comes from the photosphere; a relatively thin layer, a few hundred km thick. The photosphere of the Sun is in radiative equilibrium, getting neither hotter or colder on average. What this means is that the emission processes that produce the radiation that escapes from the photosphere, are the inverse of the absorption processes that ...


2

Stars undergo nuclear fusion of chemical elements in their cores. The outward pressure of the resultant radiation and the thermal pressure from the plasma counter-act the impending collapse from the inward gravitational pressure of the star. Thus, a star is a delicate dance between outward and inward pressures. Eventually, the star runs out of nuclear fuel ...


21

The origin of sunlight is the hot plasma at and near its surface. It can be reasonably well described by Planck's black body radiation. Check out https://en.m.wikipedia.org/wiki/Sunlight and sources therein.


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