PHYS 005 Lecture Notes - Lecture 7: Weakly Interacting Massive Particles, Vera Rubin, Gravitational Lens
5 Jul 2018
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4/16 Session 7
Ch. 23 Sect. 4
Tess is looking for worlds that are similar to ours in the galaxy
The Rotating Galaxy
Hydrogen is the most abundant element in the Universe- 75%
●At some time, the 1 electrons flips
-> emits light- radio emission-> EVERYWHERE
●In the disk
of the milky way
Doppler effect has to do with sound
●Blue, red
●Towards you- HIGHER FREQUENCY
●Away fr you- LOWER FREQUENCY
Use doppler shift to determine which hydrogen blobs are moving away/toward us
●Disk is rotating
●Also w. CO in galaxy
○4 spiral arms coming fr. center
■Stars gas, and dust all follow rotation
●NEEDS TO STAY ROTATING, or it would collapse into black hole of milky
way
●Mass creates gravity
●More mass, more gravity,
●Gravity pulls things toward it
○Sun has the most mass in the solar system, why don’t planets fall to sun?
■Planets don’t fall into sun because of CENTRIPETAL FORCE
●Orbital speed of planets
○Closer you are to the sun, the faster you need to be going to not
fall in
■Mercury almost 50 km/s
■Earth- 30 km/s
How does the Milky Way Spin?
** outermost stars don’t move the fastest- move slower, lags behind
●Galaxy does not rotate as a solid disc
○Each part moves @ a different speed
***wait so how does sun rotate around milky way? I thought it was inside the milky way...
EQUATION- Period for circular motion
1. P=(2pi(r))/v
a. **unnecessary to change units
b. Period for circular motion- how long you take to make a full circle (time)
c. Period is in seconds
d. r= radius
