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Lecture 4

PCS 181 Lecture Notes - Lecture 4: Galaxy Zoo, Globular Cluster, Horse Length

Course Code
PCS 181
Margaret Buckby

of 5
Class 7
Globular Clusters
A globular cluster is a spherical distribution of ~105 to 106 stars.
Typically only a few hundred light years across….
Density is 0.4stars/pc3 to 1000 stars/pc3
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.
H0 = 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, nLo,
Then, a rough estimate of its mass is n times the mass of the Sun, nMo.
The Milky Way is estimated to have a luminosity of LMW ~ 1 x 1011 Lo.
Provide a rough estimate of its mass
MMW ~ (1 x 1011) (1.99 x 1030 kg)
MMW ~ 2 x 1041 kg
**need to know multiply luminosity of galaxy to mass of the sun
Mass range of galaxies
Galaxy masses range from ~1 x 105 Mo to ~1 x 1013 Mo.
Our galaxy, the Milky Way, has a mass of ~5.8 x 1011 Mo
=1.2 x 1042 Mo
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
massive galaxy.
Obvious spirals have NOT undergone major collisions.
Morphology of Ellipticals
Ellipticals rotate more slowly than spirals.
Born in a quiet environment???
Ellipticals contracted faster and triggered early star formation that used up their dust and gas.
When two galaxies collide, the spiral arm is destroyed and turns into giant ellipticals when
everything settles down
Galactic Cannibalism: mergers of galaxies produce a giant elliptical at the ~center of a group of
Quasars = quasi-stellar objects = qso’s
~1960 Spectra were obtained for
Two blue star-like objects: 3C48 and 3C273
Their spectral lines could not be identified….until….
~1963 Maarten Schmidt identified the EXTREMELY red-shifted Hydrogen lines
= large delta lamda
Because Vr is proportional to delta lamda, the radial velocity of Quasars is large.
Because Vr is proportional to d, the distance to the Quasars is great.