ASTR 1020 – April 11 . Final Problem Set Due Today Next Observatory Night April 17 Next Exam April 20 Website http://casa.colorado.edu/~wcash/APS1020/APS1020.html

M31 The Great Nebula in Andromeda

Our Region 15,000,000pc Local Group Virgo Cluster M81,82

Hubble Sequence (not an evolutionary sequence!)

Elliptical Galaxy

M87 in Virgo Cluster

Mass of Galaxies From Orbital Considerations Orbital velocity of stars binary galaxy orbital velocities clusters of galaxies They All Show Dark Matter

Rotation Curves Without Dark Matter Hydrogen emits a radio emission line at l = 21cm Doppler shift allows us to measure orbital velocity of gas clouds vs radius

Dark Matter Mass to Light Ratio: Mass in Solar Masses divided by Luminosity in Solar Luminosities Sun has M/L of 1 (by definition) Rigel M=20 L=2000 -- M/L = .01 Pros Cen M=.1 L = .001  M/L = 100 Galaxies typically have M/L of 7 to 10 Something like 85% of the mass is dark matter

Dark Matter Dark matter is in Ball  We can measure its distribution even though we don’t know what it is. Dark Matter Regular Matter

What is Dark Matter? WHAT IS DARK MATTER????? Some possibilities: Ionized Gas Small Stars Planets Baseballs Black Holes Neutrinos Neutralinos A flaw in Newton’s Laws MAssive Compact Halo Objects (Machos) Weakly Interacting Massive Particles (Wimps) Astronomers don’t know what most of the matter in the universe is!

Galaxies are Close Together Unlike stars, they run into each other. 30,000pc wide, but only 500,000pc apart Stars million miles wide but trillions apart

Bullseye!

Cluster of Galaxies

X-ray Clusters Over last 10 Billion years there have been many galaxy collisions in these crowded clusters. When two galaxies pass through each other stars will continue on their original path – more or less. Interstellar gas clouds collide and cannot pass through each other. They get stripped and pass into the gravitational well of the cluster. This fills with very hot shocked gas over time. So hot it emits x-rays. Shows matter distribution. (Mostly dark matter again.)

Coalescence After galaxies collide, on average, the friction causes them to drop down toward the center. Eventually they settle to the bottom.

CD Galaxy A Galactic Cannibal M87 has eaten 100 of its own.

Gravitational Lenses Einstein predicted light bends as it goes around massive objects. Just like an orbiting body.

The Distance Scale All the things astronomers have done to gain a handle on distance

Solar System Distances to 3AU Radar Measure time of flight of signal bouncing off planets Transit of Venus Captain Cook in Hawaii Time that Venus hits limb of Sun

Parallax to 100pc I year cycle

Main Sequence Fitting to 55,000pc Plot enough stars and the Main Sequence becomes clear. This works out to Magellanic Clouds. Beyond that, MS stars too faint

Cepheid Variables to 100Mpc

Period-Luminosity Relationship Cepheids are bright and can be seen at very large distances.

Type I Supernovae All Type Ia supernovae are the same brightness. That white dwarf that implodes and then explodes is always about the same. And they’re bright. You can see them at billions of parsecs! Apparent magnitude can be converted to distance.

Tully-Fisher Relation The brighter the galaxy is, the faster it rotates. Use radio spectrum to measure Doppler width. Not super accurate, but it works.

The Distance Scale

Redshift of Galaxies Hubble found that galaxies are redshifted. The absorption lines are those of the stars that make up the galaxy.

Hubble’s Law The more distant the galaxy, the greater the redshift. The more distant is the galaxy, the faster it is flying away from us. H0=70 km/s/Mps

Example Galaxy in Virgo Cluster is at 15Mpc will recede at v = 70 km/s/Mpc x 15Mpc = 1050km/s dl = l x v/c = 4000Å x 1050/300,000 = 14Å a 4000Å line will appear at 4014Å

Example 2 l0 = 1216Å but is observed at l = 1228Å dl = 12

A Modern Hubble Diagram

Galaxies are Flying Apart Galaxies remain same size. They just get farther apart. Effect is the same no matter which position you occupy

Expanding Universe Current Universe The volume of the universe is increasing. Early Universe

The Age of the Universe Notice: At time zero, d = 0 All galaxies are at zero distance! The universe has zero volume! when t=1/H

The Beginning Before 13 billion years ago, there was no before. Time and space started with the Big Bang We will return to this in a few more lectures

Galaxies are Moving Gravity attracts them to mass centers.

Redshift Survey Galaxies across the sky. Distance from redshift. “The Great Wall”

More Galaxies

The Texture of the Universe

Theory of Structure Structure grew out of minor fluctuations. Gravity causes density regions to enhance. The very origin of structure.

The Cosmic Web