Lecture 13-Chapter 21-Galaxy Evolution

36 views3 pages
Chapter 21 ± Galaxy Evolution
x Models for galaxy formation:
x Hydrogen and helium filled all of space more or less uniformly when the universe was
very young
x The distribution of matter in the universe was not perfectly uniform ± some regions
denser than the others.
Why Galaxies Differ
x Protogalactic Spin: a galax\¶VW\SHPLJKWEHGHWHUPLQHGE\WKHVSLQRIWKH
protogalactic cloud from which it formed.
x If the original cloud had a significant amount of angular momentum, it would have
rotated quickly as it collapsed, resulting in a spiral galaxy.
x If the protogalactic cloud had little or no angular momentum, its gas might not have
formed a disk at all, resulting in an elliptical galaxy.
x Protogalactic density: DJDOD[\¶VW\SHPLJKWEHGHWHUPLQHGE\WKHGHQVLW\RIWKe
protogalactic cloud from which it formed.
x With high gas density would have radiated energy more effectively and cooled more
quickly, allowing more rapid star formation.
x If the star formation proceeded fast enough, all the gas could have been turned into
stars before any of it had time to settle into a disk, resulting in lacking a disk, making
it an elliptical galaxy.
x A lower-density cloud would have formed stars more slowly, leaving gas to form disk
of a spiral galaxy.
Galactic Collisions
x Galaxies rarely evolve in perfect isolation.
x Collisions between galaxies are constantly occurring, in which a collision between two
spiral galaxies can create an elliptical galaxy.
x Tremendous tidal forces between the colliding galaxies tear apart the two disks,
randomizing the orbits of their stars.
Galaxies in Clusters
x Elliptical galaxies dominate the galaxy populations at the cores of dense clusters of
galaxies.
x Central dominant galaxies are gigantic elliptical galaxies that apparently grew to a
huge size by consuming other galaxies through collisions.
x They contain tightly bound clumps of stars, the center of an individual galaxy that was
swallowed by the giant.
x The process of galactic cannibalism can create central dominant galaxies more than 10
times as massive as the Milky Way.
x When a spiral galaxy cruises through the center of a galaxy with very hot gas, the hot
JDVH[HUWVGUDJIRUFHVWKDWVORZWKHJDOD[\VJDVEXWQRWLWVVWDUV
x Its disk will eventually fade, while its bulge and halo will remain prominent.
x If the disk has already formed a large number of stars when its gas is stripped, the
remaining galaxy will look like a spiral galaxy without its gaseous disk, a lenticular
galaxy.
www.notesolution.com
Unlock document

This preview shows page 1 of the document.
Unlock all 3 pages and 3 million more documents.

Already have an account? Log in

Document Summary

N hydrogen and helium filled all of space more or less uniformly when the universe was. N the distribution of matter in the universe was not perfectly uniform  some regions denser than the others. If the original cloud had a significant amount of angular momentum, it would have rotated quickly as it collapsed, resulting in a spiral galaxy. If the protogalactic cloud had little or no angular momentum, its gas might not have formed a disk at all, resulting in an elliptical galaxy. N protogalactic density: ,,,895029-0/0907230/-90/0389419e protogalactic cloud from which it formed. N with high gas density would have radiated energy more effectively and cooled more. If the star formation proceeded fast enough, all the gas could have been turned into stars before any of it had time to settle into a disk, resulting in lacking a disk, making it an elliptical galaxy.

Get access

Grade+
$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
Booster Classes
Class+
$8 USD/m
Billed $96 USD annually
Homework Help
Class Notes
Textbook Notes
30 Verified Answers
Study Guides
Booster Classes