MadSci Network: Astronomy
Query:

Re: Why do pictures of galaxies resemble hurricanes?

Date: Mon Oct 9 23:11:36 2000
Posted By: Ken Rines, Grad student, Astronomy, Harvard-Smithsonian Center for Astrophysics
Area of science: Astronomy
ID: 969506084.As
Message:

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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