Expert: Jayendra Upadhye - 7/4/2005

Question
I have studied about black holes.

But found some contradictory informations from google and other sources.

1..I want to ask whether this black hole really exists or not?
2.. If it exists really then what is the actual theory of "Stephen hawking" about black hole?
3.. How far is the black hole is from our planet?
4.. I can't understand the time in Astronomical units please explain those units with the original easy to understand units.

Thank you.
Usman Zafar Paracha.

Answer
Usman,
1 - There is a candidate known for quite a time, the
   x ray source cygnus x-1.
   At the core of our galaxy is a million solar mass black
   hole.
   There are suspected black holes in centers of huge
   elliptical galaxies too.
   And looking at the large scale structure of the
   universe, most galaxies in our vicinity are rushing
   headlong towards a "great attractor in the virgo super
   cluster of galaxies! This unseen mass is pulling many
   many galaxies including our local group towards the
   constellation virgo.
2 - I am not fully aware except hawking predicts that
   energy does manage to radiate away from black holes as
   hawking radiation.
3 - Usman, there is no particular "documented" black hole
   as such that one can say "hey that one is so far from
   earth!"
4 - Time in terms of "distance" is only by analogy.
   When you say "newyork is just 2 hours away" from such
   and such a place, you dont mean it is 2 hours behind or
   ahead in time! It is just a figure of speech ..a way of
   making the guy realise how far it is, when he is flying
   or driving.
   Since the speed of liht is an invariable constant all
   over the universe, one uses "years" in place of "hours
   to newyork" when conveying how far an object is.
   Saying it is one light year away, simply means "seconds
   1 year times 300,000 km" away.

   To best of my knowledge, "astronomical unit or AU" is a
   measure of pure distance, and is not ised in time -
   distance analogies.

Hope that is clear.
Jayen