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Astronomers who are using the
Hubble telescope have found unexpected mysteries. The
black hole photo on this page and the 800 light year
wide spiral shaped disk of dust feeding it, are slightly
offset from the center of the host galaxy NGC 4261. Most
astronomers call a black hole black because light cannot
escape from it. A black hole's escape velocity is
greater than the speed of light. Escape velocity is the
velocity that an object, for example a space ship or a
planet needs to escape from the gravitational pull of
another more massive object such as a planet, a star or
a galaxy. Eventhough no light or energy can escape from a
black hole, these bizarre objects can still be powerful sources of energy in the
universe. If a black hole with the mass of 10 suns is surrounded by a cloud of
interstellar gas and dust, the parts of the matter will be far enough from the
black hole that it will either escape its gravitational pull or merely go into
orbit around it. The Schwarzschild radius is more commonly called the event
horizon.The horizon on Earth is the limit of our range of vision caused by the
curvature of the Earth's surface. We cannot see what is happening beyond the
horizon, in case of the black hole the curvature is of space time itself. In the
past years we learned more and more about black holes. They really exist in the
universe and in our Milky Way galaxy.
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A common type of black hole is the type produced by some dying stars. A star
with a mass of about 10 - 20 times the mass of our Sun may produce a black
hole at the end of its life. In the normal life of a star there is a
constant tug of war between gravity pulling in and pressure pushing out.
Nuclear reactions in the core of the star produce enough energy to push
outward. For most of a star's life, gravity and pressure balance each other
exactly and so the star is stable. However, when a star runs out of nuclear
fuel, gravity gets the upper hand and the material in the core is compressed
even further. The more massive the core of the star, the greater the force
of gravity that compresses the material, collapsing it under its own weight.
Astronomers found with accuracy an immense black hole in the milky way
galaxy with a mass of more than 2 Million Suns. |
