Lecture 6 – February 5
1. Disk Population: A group of stars that orbit the galactic
center, in a disk shape. (flat) (consists of stars made after
the gas in the protogalactic cloud settled into a rotating
2. Protogalactic Cloud: When clouds were formed in the
early universe ( 70% hydrogen, 30% Helium) These
clouds form galaxies.
REMEMBER THIS: Gas back in time was equally
distributed, but than that gas started to move in the
most dense areas, which than became a center- (the
gas is called Protogalactic cloud) The center is what
you call a galaxy.
3. Spheroidal Population: A more random design of
orbiting. (random oriented orbits) (Consists of stars that
were brown before it’s galaxies rotation)
4. WHY ARE GALAXIES DIFFERENT?
There are 2 hypothesis for this condition:
a) The galaxies differ because their protogalactic clouds had
slightly different conditions.
b) Galaxies may have started similarly to the other galaxies, but later changed
because they interacted with other galaxies.
5. SPIRAL GALAXIES HAVE GAS-RICH DISKS , ELLIPTICAL
GALAXIES DO NOT:Why ? Either because of a
Protogalactic spin , or the Protogalactic Density.
6. What is a Protogalactic Spin, and Protogalactic
Density? Protogalactic Spin: Well it is basically Protogalactic spin is
when the angular momentum, defines the type of orbit it
will be, Elliptical/ Spiral. Etc. For example, if the cloud has
a certain number of angular momentum it would rotate
quickly than collapse, this would result into a spiral . If
the protogalactic cloud had little or no angular
momentum, than it would result in having no disk, thus
resulting in a elliptical galaxy.
Protogalactic Density: High gas density- radiates more
energy than low gas density . (opposite)