ASTRON 1F03 Lecture Notes - Lecture 23: Spiral Galaxy, Galaxy Merger, Gravitational Lens
18 Dec 2015
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Document Summary
The stars and gas in the galaxy orbit in the overall gravitational field. Elliptical galaxies; stars orbit in many different directions, maintaining the elliptical shape. Spiral galaxies have a thin disk: orbits are circular and all nearly in the same direction. Stars in the central bulge of a spiral galaxy also have orbits in many directions (like an elliptical galaxy). Spirals: large, lots of gas and net rotation. Ellipticals: large or small, not much gas, little net rotation. Not in isolation spirals probably stay spirals, etc. Colliding spirals is probably one way to make ellipticals. iclicker: what physically collides in a galaxy merger: stars, dark matter, gas, all of the above, nothing. The milky way and andromeda may collide like this. Orbital speeds of stars and gas depend on total amount of mass in the galaxy. Luminous matter (normal matter) cannot produce all the gravity in a galaxy. Gm ( r) r2 v constant = > m (< r) r.
