The Online Library of Knowledge


Black holes

A spiral galaxy with a black hole at its centreA spiral galaxy with a black hole at its centreClick to play videoBlack holes are tiny regions of space with a force of gravity so strong that nothing, not even light, can escape from them. All bodies in space have a gravitational pull, the force that attracts other things towards them. The greater an object, the stronger its pull and the harder it is to escape from it. A rocket must go faster than 40,000 km/h (25,000 mph) to escape Earth’s gravity. It would have to exceed 2 million km/h to escape from the Sun, which is a far more massive object than Earth. What if an object were so massive, something would need to travel faster than the speed of light to escape its pull? But we know that nothing can travel faster than light, so light itself could never escape. That object is a black hole.

A supernova remnant with a dead star at its centreA supernova remnant with a dead star at its centre

Super-dense bodies

Where might such a massive object be found? Very large stars, some with more than 10 times the mass of the Sun, burn up their fuel in a much shorter time—a few million years, compared to the Sun’s 10 billion years. They swell into massive supergiants before blasting apart in incredibly powerful explosions called supernovas. A supernova’s core compresses in seconds down to a tiny, super-dense body called a neutron star. Its gravitational pull is so strong that even light rays would be pulled back in towards it, so the object is invisible: a black hole.

Quasars are among the most luminous, powerful and energetic objects known in the Universe. About the same size as the Solar System, they may give off up to a thousand times the energy of the Milky Way Galaxy.

© 2020 Q-files Ltd. All rights reserved. Switch to Mobile