01:750:109 Chapter Notes - Chapter 11.2: Galaxy Formation And Evolution, Spiral Galaxy, Elliptical Galaxy
Why do galaxies differ?
●Galaxy evolution
is the formation and development of galaxies
●Early stages in formation of galaxies thought to be similar to the Milky Way
○Gravity pulling matter into a protogalactic cloud system that contracted and began to
from stars
○Blah blah spirals with gas-rich disks
○BUT galaxies like ellipticals lack disks
●Key issue: why some galaxies ended up with elliptical and others w spirals
●2 possibilities:
○Galaxies may have ended up looking diff bc they began w slightly diff birth conditions in
their protogalactic clouds
○Galaxies may have begun their lives similarly but later changed bc of interactions w
other galaxies
Birth Conditions
●Traces back to a galaxy's type back to the protogalactic clouds from which it formed
●2 factors may play a role:
○Galaxy's type determined by the rotation of the protogalactic cloud system from which
it formed
■If original system has sign. amount of angular momentum, it would have rotated
quickly as it collapsed
■Galaxy produced would therefore have tended to form a disk and
resulting galaxy would be a spiral galaxy
■If had no angular momentum, its gas might not have formed a disk at all, and
the resulting galaxy would be elliptical
○Galaxy's type determined by the density of the protogalactic clouds from which it
formed
■Protogalactic clouds w relatively high gas density would have radiated energy
more effectively and cooled more quickly --> allowing more rapid star formation
--> all the gas could have been turned into stars before any of it had time to
settle into a disk --> aka lack a disk, making it an elliptical galaxy
■Lower density clouds would have formed stars slower, leaving plenty of gas to
from a disk of a spiral galaxy
Later Interactions
●These prob not the whole story bc: galaxies rarely evolve in perfect isolation
●Collisions btwn two spiral galaxies can create an elliptical galaxy
Document Summary
Galaxy evolution is the formation and development of galaxies. Early stages in formation of galaxies thought to be similar to the milky way. Gravity pulling matter into a protogalactic cloud system that contracted and began to from stars. Key issue: why some galaxies ended up with elliptical and others w spirals. Galaxies may have ended up looking diff bc they began w slightly diff birth conditions in their protogalactic clouds. Galaxies may have begun their lives similarly but later changed bc of interactions w other galaxies. Traces back to a galaxy"s type back to the protogalactic clouds from which it formed. Galaxy"s type determined by the rotation of the protogalactic cloud system from which it formed. If original system has sign. amount of angular momentum, it would have rotated quickly as it collapsed. Galaxy produced would therefore have tended to form a disk and resulting galaxy would be a spiral galaxy.
