What lies at the very centre
of our galaxy?
Clue: it's 4 million times as massive as our
Sun, but fits into a space smaller than our Solar System.
Any ideas? There's only one thing that scientists know of that
can be so small and yet so massive - a black hole.
Black holes are one of the great mysteries of our universe.
Scientists think that black holes can be smaller than an atom or a
billion times more massive than our Sun.
A black hole is a place in space where the gravitational pull is
so strong that not even light can get out. Their huge gravitational
pull can rip stars apart. Have a look at this animation of a black
hole destroying a star:
When a black hole destroys a star, it tears matter from the
star's surface and drags it into orbit around the black hole. This
matter gets superheated and starts to spin around the mouth of the
black hole. Huge jets of radiation fire from the core of the black
hole, which can be seen across the cosmos.
 nasa_473x355.jpg)
Two blacks holes emitting
radiation at the centre of galaxies (c) NASA
Because no light can get out, people can't see black holes -
they are invisible. So how do we find them? Scientists can see how
the huge gravitational pull affects the stars and gas around the
black hole. They can also detect the enormous jets of radiation
emitting from the centre of the black hole.
At the mouth of the black hole is the event
horizon. At this point, even light can't escape the
gravitational pull of the black hole.
The centre of a black hole is called the
singularity. Even though we can see radiation
escaping from a black hole, its centre is a mystery. What is
happening there? No one knows. That's for the next generation of
physicists - you - to work out.
Find a black hole! Explore the night sky with the Hubble
telescope and see if you can find a black hole:
http://hubblesite.org/explore_astronomy/black_holes/modules.html
Main image (c) NASA/JPL-CalTech