AST201H1 Lecture Notes - Lecture 6: Bullet Cluster, Semi-Major And Semi-Minor Axes, Galactic Center

51 views3 pages
25 Aug 2016
AST201 Week 6
Our Galaxy: The Milky Way
- The center of the our galaxy has a mass of 4 billion solar masses
- Every galaxy has a supermassive black hole at the center and stars orbit around it
- From largest to smallest: universe, galaxy, solar system, star
- If you were in the center of a cluster of stars/ on a planter in the center of a symmetric
sphere of stars you would see the stars filling your sky roughly equally in all directions. If
you stood somewhere to one side of a disk of stars you would see the stars as a thin band
of light circling your sky
- The dark places are where dust is blocking starlight because visible light is easily blocked
by dust. Longer wavelengths of light are not. The wavelength of infrared light is larger
than the size of a dust particle. Dust tends to block visible light (short wavelength) but
allow infrared light (longer wavelength) to pass
- The Milky Way in visible light – you cannot see through most of the dust. The Milky
way in short wavelength infrared light – you can see through most of the dust. In long
wavelengths infrared light – you see the cool dust itself, not the hot stars
- We can determine the mass of the Milky Way from outside the Sun’s orbit from the orbit
of stars and gas clouds orbiting the galactic center at greater distances than the Sun
Properties of the Milky Way
- Out galaxy holds more than 100 billion stars.
- It is a spiral galaxy because of its spiral arms, which are part of a flat disk of stars found
in clusters that are of all ages, masses and colors
- The disk surrounds a bright central bulge.
- The entire disk is surrounded by a dimmer, rounder halo where most of the old stars
reside in. The most prominent stars in the halo are found in globular clusters of stars:
densely packed spheres of hundreds of thousands of very old stars, evenly distributed
around the galaxy
- Stars in the disk orbit in roughly circular paths that all go in the same direction in nearly
the same plane. Stars in the bulge and the halo soar high above and below the disk on
randomly oriented orbits
- Formed around the same time, relatively the same mass, yellow-orange hue.
oGiven their appearance, the rate of star formation in globular clusters compared to
the disk of the galaxy is low  blue stars are where the star formation is
find more resources at
find more resources at
Unlock document

This preview shows page 1 of the document.
Unlock all 3 pages and 3 million more documents.

Already have an account? Log in

Get access

$10 USD/m
Billed $120 USD annually
Homework Help
Class Notes
Textbook Notes
40 Verified Answers
Study Guides
1 Booster Class
$8 USD/m
Billed $96 USD annually
Homework Help
Class Notes
Textbook Notes
30 Verified Answers
Study Guides
1 Booster Class