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Q: What is at the end of a Black Hole? What is the distance of a Black Holes gravity? What would happen if a Black Hole swallowed a star?
-- Don

A: Black holes evaporate slowly by radiation. This takes very long for solar mass black holes, but for very small black holes it can be very quick. Gravity has an infinite range. Black holes are not any different in terms of their gravity than any other stars of the same mass. The star will be torn apart by tidal forces, and the gravitational energy will be released as a burst of radiation.

Q: What's the current understanding of the conditions required for a supernovae? How are elements heavier than iron formed in supernovae..what are some typical reactions? Any idea where the supernovae was located that supplied the elements for our sun and earth?
-- Robert E. Barry, Ann Arbor, MI

A: Supernovae form either from the cores of massive stars which collapse, when the cores are coposed of iron (and reach temperatures of about 10^10 Kelvin), or from white dwarfs which grow in mass beyond the critical limit of 1.4 Msun. The heavy elements are formed by nuclear reactions under explosive conditions, when neutron captures proceed faster than radioactive beta decays. We do not know which supernova trigerred the formation of the solarsystem, although some speculations about the Geminga pulsar were made.

Q: After watching a PBS program some years ago entitled 'A Brief History of Time', featuring Steven Hawking, I was amazed that such a respected scientist could admit that he had made mistake about his views on the Big Bang, and the beginning of time. Is this common among cosmologists? Also, if all of our physics become meaningless at the beginning of a black hole, then isn't it somewhat discouraging to scientists who are pursuing an understanding of them?
-- Reginald Wilson

A: The way scientific progress is achieved is by constructing theories which can explain the presently available observations and experiments. When new observations which contradict the existing models are made, the models are modified to be consistent with all the available data. From the point of view of an outside observer, black holes are only seen to their event horizon. All of that is perfectly describabale in terms of the physics we know. Only when we look from the inside at the singularity, things become more complicated, but even there, progress is being made.

Q: In the program about stars and black holes they mentioned that they believe the matter pulled into a black hole might leave this universe and enter another. If that is so why is there still a gravitational effect from a black hole if the matter is no longer in this universe?
-- Anonymous

A: From the point of view of an outside observer, the matter that goes in never crosses the event horizon (although it gets nearer and nearer), so the gravitational force always remains.

Q: If we use the Schwarzschild radius as a criteria, the universe is a "BLACK HOLE"!! By the way, is there an acceptable abbreviation for "Schwarzschild"?
-- Bill Jjones, Sierra Vista, AZ

A: No, abbreviations are not used.

Q: Dear Deepspace: I am looking for a complete list of the 4000 or so known stars within a 20 Parsec radius of Sol, Names, ID's, available facts about them, exact positions and if a 3d Map exists. Please let me know if a place, RL or WWW, exists where I can get this information. If it does not exist, could you suggest references so I can accumulate and compose it? Thanks.
-- Wesley Miley

A: Probably the best source for this would be the: Gliese Catalogue.

Q: I am aware of the experimental evidence supporting Einstein's theory explaining the bending of starlight as it traverses the sun's gravitational field. But, conceptually I have great difficulty accepting the idea of the theory, e.g, the warping of space surrounding the sun due to its intense gravitational field. But, my instinctive response always is how can you warp what is there? What is being warped?

Was the possibilty of weak interactions between gravitational and photon fields ever considered? Would this alternative approach necessarily violate the relativistic requirement that only particles of zero mass move at "c" velocities.? And. therefore, forbids the existence of such interactions.

Can you shed any light on my dilemma?
-- Tony Immarco

A: Even if you do not think in terms of warped space, you can convince yourself quite easily that photon energies are effected by gravity (redshifted), otherwise we could get infinite amounts of energy by just emitting photons up and down a gravitational potential and converting them to particles. Gravitational lenses have now become so common, that there is no doubt about how light is affected by gravity.

Q: Is there anything to lead us to theorize there might be an opposite object? A point expelling matter out into the Universe.
-- Vernon Pierce

A: "White holes" (which would do what you suggest) are possible solutions of the field equations, however, there is no observational evidence for such objects.

Q: How or what do the scientists featured in the programs think about quantum physics? According to that theory nothing around us is static, but the outcome of observations and measurements depends on the interaction with an observer. In that case consider the following, quoted from the book "Parallel Universes" by Fred Alan Wolf. "When the universe first began, no attempt was made to differentiate one possible evolving universe from another. All possible universes existed in a superimposed state acting as a single universe, according to the parallel worlds concept. Nothing was defined. The universe at that time did not possess a well-defined radius. But then a mysterious interaction occurred. The universe split into several, perhaps an infinite number of parallel outcomes, each specifying a radius for its universe. How did this happen? In order for this to have happened there had to be an observer, but who, at that time?
-- Conny Jensen, Greeley, Colorado

A: The "many world interpretation" of quantum mechanics is only one way to deal with the idea that there are only probabilities, and what we see is only one of many possibilities. It is very difficult to distinguish between such an interpretation and one which merely discusses probabilities. In any case the idea is that interactions are needed to make certain states happen, these can be with particles, they don't require humans.

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