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Black Hole

A black hole is a region of space from which nothing, including light, can escape. It is called "black" because it absorbs all the light that hits it, reflecting nothing.

The theory of relativity says that this must be the case and happens as the result of the deformation ofspacetime by a very compact mass. Therefore the black hole is not thought of as a 'hole' at all... it is a concentration of very dense matter.

Around a black hole there is an undetectable surface which marks the point of no return, called an event horizon. beyond that horizon no information gets back out.

  • How can we 'see' a black hole?

A black hole can onlybe observed through its interaction with other matter. It has a very strong gravitational pull on matter. If you track the movement of a group of stars you can see this effect of the black hole . Alsoy, when interstellar gas gets pulled into a stellar black hole from a companion star, the gas spirals inward, heating to very high temperatures and emitting large amounts of radiation that can be detected by telescopes.

  • Is there a black hole at the centre of every galaxy?

Astronomers have found evidence of really big black holes at the center of galaxies. After observing the motion of nearby stars for 16 years, in 2008 astronomers found compelling evidence that a supermassive black hole of more than 4 million solar masses is located in the center of the Milky Way galaxy. (See BBC news report)

(A  solar mass (M☉) =  1.98892×1030 kg. It is a unit of mass in astronomy. It is equal to the mass of the Sun, about two 'nonillion' kilograms and is used to express the masses of stars and galaxies.)