A globular cluster is a spherical distribution of ~10 to 10 stars.
Typically only a few hundred light years across….
Density is 0.4stars/pc to 1000 stars/pc 3
Formed early in the life of a galaxy and contain the oldest stars known.
Follow RANDOM paths through their home galaxy = do NOT move ~ circularly in the plane (disk)
of the galaxy as most stars do.
They are found above, below and within their galaxy.
H 0 V/d
The Hubble Classification System
- Spiral (S)
- Barred Spiral (SB)
- Ellipticals (E)
- Irregulars (Irr)
- See handout for characteristics of each type
You can assist the SLOAN Galaxy Survey
Galaxy Zoo: Hubble
Color of Galaxies
- The color of galaxy is the sum of color contributions from its stars
- Ellipticals: reddish-orange from old stars
- Spirals: central bulge is reddish-orange from old stars there.
- Spiral arms are blue from the presence of hot young stars (forming from the gas and
dust in the arms) - Irregulars: contain largest amounts of dust/gas are the blue-est galaxies known and
support the most active star birth
What are the blue-est galaxies? Irregulars test question
***Know the handout for the Midterm test #1***
30 multiple choice questions 25 conceptual and 5 math questions
Luminosity = L = Total energy emitted each second
Equation for L is on formula sheet
R is radius
T is temperature
Approximate Mass of a Galaxy
In the luminosity, L, of a galaxy is n times the luminosity of the Sun, nL
Then, a rough estimate of its mass is n times the mass of the Sun, nM o
The Milky Way is estimated to have a luminosity of L MW ~ 1 x 10 L o
Provide a rough estimate of its mass
M MW ~ (1 x 10 ) (1.99 x 10 kg)
M MW ~ 2 x 10 kg
**need to know multiply luminosity of galaxy to mass of the sun
Mass range of galaxies
Galaxy masses range from ~1 x 10 M to o1 x 10 M . o
Our galaxy, the Milky Way, has a mass of ~5.8 x 10 M1 o
=1.2 x 10 M o Morphology of Spirals
Spirals spin faster than ellipticals ->
Higher angular momentum, L = mvr.
Born in a turbulent environment???
Spirals form/contract slowly and have gas/dust to support ongoing star birth.
Spiral structure is extremely delicate and would be destroyed in a collision with another
Obvious spirals have NOT undergone major collisions.
Morphology of Ellipticals
Ellipticals rotate more slowly than spirals.
Born in a quiet environment???
Ellipticals contracted fast