Supernovae

A supernova flares up until it is briefly brighter than the hundred billion fellow stars of its galaxy. The heavy atomic nuclei that it has synthesized at the end of its life are flung across space, mixing with the interstellar nebulae and forming raw materials for new planetary systems around new stars, whose formation may be triggered by the shock waves emanating from the supernova.

Remnants of supernova explosions can be seen as enormous rings and globe of gas. At the centre there may remain a fragment of the original star, with a mass similar to the Sun’s enormously compressed into a sphere perhaps 20Km across. Here electrons and atomic nuclei are crushed together to form a ball of neutrons (the uncharged particles found in the heart of all atoms). One teaspoon full of this neutron star, or pulsar, has a mass of 100 million tones. Beams of radiation jet from its poles generated by gas falling on to it and focused by the neutron star’s stars intense magnetic field. The star spins a few tens or hundreds of times a second, and if one of the radiation beams sweeps across the direction of the Earth, we observe it as pulsating radio source or pulsar.

When a star of around ten solar masses a supergiant dies, the remnant it leaves may be even denser than a neutron star, and becomes a black hole. The gravitation of such a body is so intense that it begins a collapse that continues for ever towards a geometric point ; the more it shrinks the stronger its gravity becomes Neither radiation nor matter can escape from within a sphere only a few kilometers across, the boundary of which is called the even horizon. Such matter has effectively left the universe.

But paradoxically black holes can be at the heart of intensely bright objects. Gas falling into a black hole- perhaps from a companion star- releases enormous amount of energy, much of it at very short X ray wave length.