SOLAR
SYSTEM
STARS
BLACK HOLES
METEORS
AND METEORITES
ASTEROIDS
COMETS
GALAXIES
NEBULAE
GLOSSARY
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Black
Holes
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"A
region of space-time in which there is such an immense concentration
of material within a small volume that space-time curves over on
itself and matter and energy cannot escape".
The variable possible evolutionary
paths that stars follow in their life span are still under theoretical
investigations. Some calculations show that under certain conditions,
stars with mass, greater that specific value, in their last stages
of evolution, collapse very rapidly. Their densities increase to
even greater than those ascribed to be Neutron
Stars. As the density of such stars increase, so does their
gravity. A stage comes when the gravitational pull of such a star
would permit neither matter nor light to escape from the star and
it would become a Black Hole - a little universe in itself. Such
Black Holes are now the subject of much research.
If light cannot escape, then how can astronomers ever hope to detect
a Black Hole? Increased use of satellites have permitted astronomers
to study objects in the Universe that produce x-rays. X-rays are
very energetic forms of radiant energy that are blocked by out atmosphere.
One of the source of x-rays is special type of binary system of
super giant star and Black Hole. Cases from the super giant star
spill over and fall into the companion Black Hole. These gases are
heated to tremendous temperatures during their fall towards the
Black Hole and before reaching the point of no return, x-rays are
emitted into space. Therefore the existence of Black Holes can only
be determined by observations of its influence on matter and space
around it.
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CONTACT: Ray Villard, STScI Wednesday,
May 25, 1994
(410) 338-4514
PRESS RELEASE NO.: STScI-PR94-23
Dr. Holland Ford, STScI/JHU
(410) 338-4803
(410) 516-8653
HUBBLE CONFIRMS EXISTENCE OF MASSIVE BLACK
HOLE AT HEART OF
ACTIVE GALAXY
CLICK
HERE FOR PRESS RELEASE TEXT
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Black Holes till today have
not yet been fully investigated and hence what happens to the matter
which enters a Black Hole is not completely known. It is said that
in the constellation Cygnus, there is a Black Hole we call it Cygnus
X-1. It is also predicted that at the center of our Milky Way Galaxy
there lies a super massive Black Hole. The White Dwarf , the Neutron
Star and the Black Hole are now considered the ends of three main
paths of evolution that stars of various masses can take once they
have passed the Helium burning stage of their lives. What conditions
cause a star to evolve one way or the other at this point is not
fully understood. But surely it all depends on the initial mass
and the composition of the star's evolutionary progress upto this
point, together with the specific environment including the existence
of any binary companion, etc.
If theoretically, a Black Hole is the penultimate residue of a massive
star, then what happens to an average star such as the Sun, once
it has exhausted all its nuclear fuel?
It will finally become a White Dwarf. But there are atleast another
four billion years for the Sun to reach such a stage and four billion
is next to eternity for us humans on Earth!! Black Holes are formed
when matter reaches sufficiently high density. Light from a star
of low density, such as a Red Giant, is, scarcely deflected by the
gravitational field. A White Dwarf, which has a density of one tonne
per cubic cm, also does not trap light, although the light rays
are appreciably curved.
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