BLACK HOLES Black holes are often portrayed as portals to other universes in science fiction books and films. But a new theory by the famous physicist Stephen Hawking may put a damper on any cosmic travel plans.

Black holes are the burnt-out remnants of massive stars that were at least eight times larger than the Sun. It's impossible to see a black hole - not even light can escape their grasp. But we can see the stuff that is being sucked into them and torn apart by their immense gravitational forces.

Portal to another universe? I am sorry to disappoint science fiction fans. But if you jump into a black hole, your mass energy will be returned to our Universe but in a mangled form. Prof. Stephen Hawking

As debris gets closer to the mouth of a black hole, it speeds up and the bits smash together. They form a flat rotating disc that spirals into the hole. The collisions create heat and give off X-ray radiation we can detect on Earth.

Scientists, including Hawking, originally thought that all information about an object was lost once it passed a boundary in space called the 'event horizon' on its journey into a black hole. However, Hawking now thinks that objects aren't completely destroyed.

Theory suggests that over long periods of time, black holes radiate energy and slowly shrink until they disappear. Previously Hawking thought that when a black hole disappeared, information about the objects inside also disappeared, perhaps to another universe. But now he has gone back on ideas he first put forward in the 1970s.

"I am sorry to disappoint science fiction fans. But if you jump into a black hole, your mass energy will be returned to our Universe but in a mangled form."