megavideolinks
Joined: 19 Nov 2011
Posts: 273
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 Posted: Wed Dec 14, 2011 12:45 pm Post subject: Black Holes as Intergalactic Gas Heaters |
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Galaxies such as our Milky Way
are certainly not unique. They
have merged to form large groups,
which, in the case of a rich cluster,
may contain as many as several thousand members. Close to the centre of
virtually every large cluster is a giant
galaxy. The space between galaxies is
not completely empty, as appears to be
the case in pictures of the visible spectrum. To the contrary, this space is
filled with a tenuous gas. However, as
it has a temperature of many million
degrees, it only radiates in X-ray light
- something which is difficult to observe, as the earth’s atmosphere absorbs this high-energy radiation. The
discovery of this intergalactic gas in
the seventies led ten years later to a
theory which, to this day, remains hotly disputed: at that time, British astrophysicists came to the conclusion that
the gas first flows into the central area
of the cluster, where the massive
galaxy with its strong gravitational
field dominates its surroundings. Here
it cools down over a period of about a
billion years and “condenses” into new
stars. The specialists used the term
“cooling flows”. From the data available at the time, the scientists estimated that in this way, in extreme cases,
more than a thousand new stars might
form in the cooling flows every year.
An unbelievably high rate in comparison to the average spiral galaxy like
the Milky Way in which roughly one
new star lights up annually. So this
hypothetical process would contribute
significantly to the formation of
galaxy clusters.
However, this sensational theory had a
snag: neither the cool gas itself nor the
young stars formed within it could be
observed. So advocates of the theory
were keen to invent new hypotheses to
explain the discrepancy between theory and observation. For example, it
was believed that the formation of
stars in the cooling flows happens differently from the process with which
we are familiar in our Milky Way and
other galaxies. It was believed in particular that it was essentially only lowmass stars that form, which, from a
great distance, cannot be distinguished
from an old star population, such as
that existing in the central galaxy. This
was, however, in contrast to all previous experience
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