: When real physical objects become black holes, the light they emit to distant observers becomes highly redshifted as the event : horizon size is approached as seen by distant observers. The details can be found in 'Gravitation' written by Misner, Thorne and : Wheeler . As the surface of the star reaches the horizon, its light is infinitely redshifted. In the reference frame of the star's surface, as it just passes the horizon radius, it has emitted a finite number of photons just : outside of the horizon, and it is these that may escape to distant observers. The problem is that they are increasingly redshifted : as the surface emitting them gets closer to the event horizon. In the limit, the last photon is almost infinitely redshifted. Also, : gravitational time dilation occurs so that the interval between the emission of each photon lengthens dramatically as the event : horizon is approached, and the intensity of the light exponentially decreases in time. The net effect is that to the outside : observer, the surface of the star fades within a few seconds and its wavelength of peak emission shifts from X-ray to optical : energies, all the way out to infrared and radio wavelengths. X-ray astronomers recently discovered just this fading effect in the : X-ray light from a black hole a few thousand light years from Earth.

: The view is completely different from the reference frame fo the star. Nothing weird happens when the surface crosses the : event horizon radius. Even the view out into distant space may be unchanged except that incoming light get highly blueshifted as : it falls down the gravitational well of the black hole and passes the horizon. But, after passage, no light can escape the hole, and : furthermore, the mathematics show that no stable orbits are possible inside. Space-time itself is collapsing.

The only problem with this whole concept is the fact that (from the stars frame of reference) while observing the outside universe while approaching the horizon, time exponentially speeds up before our eyes till ultimately at the instant of entering the horizon the universe rapidly comes to its end! So, given this reasoning (from the stars reference point), how could anything ever enter a black hole within "our" time/space continuum? The whole concept of a black hole (starting at the event horizon) should realistically be explained that they do not and cannot exist within our dimension. And if you challenge this concept, keep in mind the fact that any mass entering into this gravity well is also exponentially time dilated to the point of infinity... Not just from our reference frame, but from the object falling as well.

• Re: Yes, but... - Paul_Rest/">Paul Rest - October 3, 1998 - 04:09 UTC
  • Time Dilation explained in illustratory fashion... - nåte/">nåte - October 6, 1998 - 05:51 UTC