Lecture 13-Chapter 21-Galaxy Evolution

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University of Toronto St. George
Astronomy & Astrophysics
Stefan Mochnacki

Chapter 21 Galaxy Evolution N Models for galaxy formation: N Hydrogen and helium filled all of space more or less uniformly when the universe was very young N The distribution of matter in the universe was not perfectly uniform some regions denser than the others. Why Galaxies Differ N Protogalactic Spin: a galax89502LJK9-009072L30-9K085L3419K0 protogalactic cloud from which it formed. N If the original cloud had a significant amount of angular momentum, it would have rotated quickly as it collapsed, resulting in a spiral galaxy. N 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: ,J,O,[89502LJK9-009072L30-9K0038L9419Ke protogalactic cloud from which it formed. N With high gas density would have radiated energy more effectively and cooled more quickly, allowing more rapid star formation. N 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. N A lower-density cloud would have formed stars more slowly, leaving gas to form disk of a spiral galaxy. Ga
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