Stellar Black Holes #2

[Shallara Navor Hevoda 0]

Let us concider what happens to radiation emited by the surface of a star as it contracts. Although what we will disuss applies to radiation of all wave lenghts, let us simply visualize standing on the surface of the colapsing star while holding a flashlight.

On the surface of a supergiant star, if we shine the beam at any angle it seems to go straight ought into space. As the star colapses, two effects begin to ocur. (We willignore the outer layers, which are unimportant here.) Although we on the surface of the star can not notice the effects ourselvs, a probe on a planet revolving around the star could detect them and transmit information back to us about them. For one thing, the probe would detect that our light beam is redshifted.

Secound, our light beam would be bent by the gravitationall field of the star. If we shine the beam straight up, it would continu to go straight up. But the further we shine it away from the verticall, the more it would be bent from the verticall. When the star reaches a certian size, a horizontall beem of light would not escape.