| Beta Particles (Beta Decay):
High-energy, high-speed electrons or positrons (antielectrons) emitted by some types of radioactive decay, when an unstable atomic nucleus with an excess of neutrons or protonsundergoes beta decay (a process mediated by the weak nuclear force). The particles emitted are a form of ionizing radiation, also known as beta rays.
Big Bang:
The huge “explosion” 13.7 billion years ago in which theuniverse (including all space, time and energy) is thought to have been created. According to this theory, the universe began in a super-dense, super-hot state and has been expanding and cooling ever since. The phrase was coined by Fred Hoyle during a 1949 radio broadcast.
Big Crunch:
One possible scenario for the ultimate fate of the universe, in which the gravity of the matter in the universe (providing that there is in fact a “critical mass”) will one day halt and reverse the universe’s expansion in a mirror image of the Big Bang, causing it to collapse into a black hole singularity. However, in the light of recent evidence for an accelerating universe, this is no longer considered the most likely outcome.
Black Body:
An idealized object that absorbs all electromagnetic radiationthat falls on it, without passing through and without reflection. The radiation emitted from a black body is mostly infrared lightat room temperature, but as the temperature increases it starts to emit visible wavelengths, from red through to blue, and then ultraviolet light at very high temperatures.
Black Hole:
The warped space-time remaining after the gravity of a massive body has caused it to shrink down to a point. It is a region of empty space with a point-like singularity at the centre and anevent horizon at the outer edge. It is so dense that no normalmatter or radiation can escape its gravitational field, so that nothing - not even light - can ever leave (hence its blackness). It is thought that most galaxies have a supermassive black hole at their heart.
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