X-ray Region of the
electromagnetic spectrum corresponding to radiation of high frequency
and short wavelengths, far outside the visible spectrum.
X-ray burster X-ray source that radiates thousands of
times more energy than our Sun, in short bursts that last only a few
seconds. A neutron star in a binary system accretes matter onto its
surface until temperatures reach the level needed for hydrogen fusion
to occur. The result is a sudden period of rapid nuclear burning
and release of energy.
zodiac The twelve constellations through which the Sun
moves as it follows its path on the ecliptic.
X
XMM/Newton The European Space Agency's large x-ray
observatory, launched on Dec 10, 1999, which is capable of sensitive
x-ray spectroscopic observations.
Y
Z
zero-age main sequence The region on the H-R diagram,
as predicted by theoretical models, where stars are located at the onset
of nuclear burning in their cores.