In 1997 and 1999 a team including researchers from the "Institut
d'astrophysique de Paris" (Paris Institute
of Astrophysics) detected visible deuterium lines belonging to
the "Balmer series" using the Canada-France-Hawaii Telescope
(CFHT). In July 2000 observations from the Very Large Telescope (VLT)
confirmed this discovery.
Hydrogen
represents 90% of the atoms in the universe, and ordinarily it consists
of one proton and one electron. A much less abundant form of hydrogen,
called deuterium, also contains a neutron in the nucleus. The conditions
required for the formation of deuterium are very particular, and probably
only occurred for a few minutes after the Big Bang. At this time the
first atomic nuclei were formed by fusion. A proton could therefore
fuse with a neutron to form a deuterium nucleus and then heavier elements.
However, the subsequent expansion of the universe prevented the fusion
of all deuterium nuclei, so the traces of deuterium which remain are
in effect fossils dating from the Big Bang.
However,
deuterium is continually destroyed by the fusion processes inside
stars which produce heavier elements, so the abundance of deuterium
in regions at various stages of evolution provides information concerning
the chemical evolution of galaxies. Thus, deuterium abundance is a
very critical parameter, and many observations are made to measure
it.
Abundance
measurements are performed by spectroscopy, which identifies elements'
characteristic spectral lines. The most frequently studied deuterium
lines are found in the ultraviolet range, which can only be observed
from space. Observation of Balmer lines, which are in the visible
spectrum, allows measurements from Earth-bound telescopes.
The
first observations from the CFHT detected a deuterium emission 5000
times weaker than the corresponding hydrogen emission. Subsequent
measurements from the VLT detected a dozen deuterium lines from the
Orion Nebula and other nebulae, and confirmed the existence of the
Balmer series. The next stage consists in the analysis of these data
to extract precise measurements of the abundance of deuterium.
