Glossary

Accretion Disc - Is the matter from a star which circles a black hole this can be easily detected from the radiation emmited from the heated matter.

Black Dwarf - The end stage of a small star, that has lost its energy and has died.

Black Hole - black holes form the stellar core from the remainder of the star that exploded as supernovae. If the core is greater than 3 solar masses then the core will contract to become a back hole. Black hole are described by there considerably strong gravity, it is so powerful that even light cannot escape. as a result of this, black holes are invisible. But they can be detected if they have a companion star. The gravity from the black hole pulls the gas from the star forming an accretion disc that circles the the black hole at great speeds, heating up and emmiting radiation. Soon after the matter from the star spirals to cross the event horizon therefore dissappearing from the visible Universe.

Hetrzsprung Russell Diagram - This is a graph in which stars can be plotted on. This includes the temperature, magnitude and spectral type.

Main Sequence - The stage in which a star has matured from being a protostar. In small stars this stage can last for billions of years, but only millions in massive stars.

Nebula(e) - This is a cloud of dust and gas inside a galaxy. Nebulae become visible when the gas begins to glow or if a nearby star is reflected against the cloud.

Neutron Star - Neutron stars are also the cores of the stars which have exploded as supernovae. This only happens when the core is between one and a half to three solar masses. They are normally 10 kilometers in diameter and consist mainly of sub-atomic particles called neutrons. These stars are so dense that a teaspoonful would weigh about a billion tonnes. Neutron stars are also observed as pulsars, they are so called because they rotate rapidly and emit two beams of radio waves, which are detected as short pulses.

Planetary Nebula - Only happens in small stars, when the helium core runs out the outer layers drift away from the core.

Protostars - Protostars are one of the first stages a star has to go through Protostars are formed from condensing matter within a cloud of dust and gas called nebulae.

Red Giant - Is an expanded small star, this happens because the helium is hot enough to convert into carbon, and the outer layers of the core begin to expand and shine less brightly.

Red Supergiant - Is the expanded massive star (see above for details).

Supernova(e) - Only happens in massive stars, it is when the supergiant collapses, sending shockwaves outwards from the star. This then forms a black hole or a neutron star.

White Dwarf - One of the final stages of a small star. it is the remainder of the of the core that slowly loses energy and dies.

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Glossary by Stuart O'Brien