1	Astro 1050 Fri., Nov. 8, 2002 Today: Articles End Ch. 12, The Milky Way Start Ch. 13, Galaxies
2	M51: The Whirlpool Galaxy
3	Density Wave Theory SPIRAL WAVE rotates with galaxy, but slower than individual stars Like moving traffic jam after an accident has been cleared Gas (and stars) catch up with wave, move through it, eventually reach front Just like cars catching up with moving traffic jam, eventually get through it Gas is more crowded in wave – clouds collapse to form new stars More collisions in the traffic jam There are slightly more old stars in the arm too, because they speed up slightly coming into it and slow down slightly moving out of it. But the best tracers are the things that mark recent cloud collapses: O,B stars, etc.
4	M51: The Whirlpool Galaxy
5	Self Sustaining Star Formation Cloud collapse Þ New stars New stars Þ Supernova after few million years Supernova Þ Shock Waves Shock Waves Þ Nearby clouds collapse Differential Rotation twists pattern into spiral
6	Two limiting cases of spirals Grand Design: Density Wave Flocculent: Self Sust. Star Form. + Diff. Rot. In most Galaxies you have some combination of the two
7	The Sun in the Milky Way
8	Milky Way Reconstruction
9	The Nucleus of the Galaxy Likely Black hole High velocities Large energy generation At a=275 AU P=2.8 yr Þ 2.7 million solar masses Radio image of Sgr A about 3 pc across, with model of surrounding disk
10	A movie of stars at the core www.mpe.mpg.de/www_ir/GC Very cool, brand new, and worth a look! This is the best evidence to date for a massive black hole at the Galactic core. Now essentially “proven.”
11	Review Chapter 12: Milky Way The discovery of the Galaxy Variable stars as distance indicators Globular clusters The size and overall structure of the Galaxy 21 cm Hydrogen emission Motions in the galaxy The Halo The Disk population Spiral Arms The Nuclear Bulge The Rotation curve and the Galaxy’s mass The origin of the galaxy The Galactic Center
12	Chapter 13: Galaxies Family of Galaxies Classification Properties of Galaxies Distance; The Hubble Law Size and Luminosity Mass (including Dark Matter) Evolution of Galaxies Clusters Mergers
13	The Hubble Deep Field
14	Types of Galaxies (pg. 254-255) Spirals Sa Sb Sc (large nuclei Þ small nuclei) (little gas,dust Þ lots of gas, dust) SBa SBb SBc (as above, with BARS) Ellipticals E0 E1 E2 E3 E4 E5 E6 E7 (spherical) (highly elliptical) Irregulars
15	Spiral types The nuclear bulge is population II (old objects) So the Sa – Sc sequence is consistent with little gas Þ more gas
16	Properties of Galaxies Distance Use Cepheid Variables for close objects Other objects for which Absolute Magnitude is know: Supernova Planetary nebula in certain emission lines Use “Hubble Law” for more distant objects (Correlation of distance with radial velocity) Diameter and Luminosity Obtain from angular size and magnitude, combined with distance Mass Rotation curves Velocity dispersion 90 to 99% of mass is “dark matter”
17	The Hubble Law using galaxies with visible Cepheid variables.
18	The Hubble Law using galaxies with visible Cepheid variables.
19	Hubble Law Example v_r = H₀ d with H₀=0.5 (mile/hr)/mile
20	Hubble Law Example v_r = H₀ d with H₀=0.5 (mile/hr)/mile
21	Hubble Law Example v_r = H₀ d with H₀=0.5 (mile/hr)/mile
22	Hubble Law Example using relative v_r and relative d
23	The Hubble Law using secondary distance indicators H_o = 72 ±8 km/s/Mpc
24	The Local Group of Galaxies Galaxies live in clusters Rich clusters: thousands of galaxies Poor clusters: Few than a thousand
25	The Coma Cluster
26	Evolution of Galaxies Galaxies live in clusters Rich clusters: thousands of galaxies Poor clusters: Few than a thousand Fundamental difference between stars and galaxies: Stars live isolated lives: They are much smaller than distance between them They virtually never collide Galaxies are not isolated They are only slightly smaller than the distances between them The can (and do) collide, and interact with gas within clusters
27	Effects of Collisions Stars pass “through” each other, but orbits around galaxy disrupted Gas clouds collide Gas stripped away from stars Collisions cause bursts of star formation Ellipticals may be those galaxies which have suffered collisions Spirals may be those galaxies which have not suffered collisions