MadSci Network: Astronomy |
Hi Keith,
You're right. Many pictures of spiral galaxies
resemble those of hurricanes on Earth. There is a fundamental connection between
the two. Galaxies and hurricanes, like everything else in the universe,
obey the same laws of physics. One of these laws is that angular momentum
is always cons
erved. Hurricanes
get their angular momentum from the atmosphere. Spiral galaxies get their
angular momentum from their local surroundings which happen to have a net
angular momentum in some direction. (Since most astronomers believe the
universe has no net angular momentum, an equally large amount of mass
elsewhere must have net
angular momentum in the opposite direction, or, more precisely, the
direction in which the angular momentum is pointed is random.) As the
galaxy collapses by gravitation, it spins faster, much like an ice skater
who brings her arms in close to her body.
The rotation speed of gas and stars in a spiral galaxy is related to the
amount of matter in the galaxy. This simple relation
has convinced many astronomers that spiral galaxies contain large amounts
of dark
matter.
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