ASTR 1020 – April 13 . Final Problem Set Due Today Next Observatory Night April 17 Next Exam April 20 Review Session Wednesday 19th Website http://casa.colorado.edu/~wcash/APS1020/APS1020.html

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

Cluster of Galaxies

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

Active Galactic Nuclei Seyfert Galaxies 1948 Radio Galaxies 1954 Quasars 1962 BL Lac’s 1968 Blazars 1980 They’re all manifestations of the same thing.

Seyfert Galaxies

Quasar QUAsi Stellar Radio source  Quasar (Sometimes QSO) Completely enigmatic 1960-1980

Huge Redshifts The Brightest Objects in the Universe

Quasar Spectrum Originally found from radio But not all have radio. Broad spectral output from radio to gamma-ray

In a Galaxy Far, Far Away Long, Long Ago

The Most Distant Quasar z=5

Host Galaxies Quasars are in host galaxies Mostly just outshine the entire galaxy

The AGN Model The Nucleus of the Galaxy is the Clot of Stars around the giant black hole that’s fallen to the bottom of the galaxy gravitational well. As more material falls in, the black hole grows and the nucleus can get very bright. I think all major galaxies have a BBH (big black hole) in the center. This is yet to be proven. Certainly a substantial fraction do.

Feeding a Quasar Accretion disk is formed of stars and clouds that wander too near the big black hole. Tidal forces rip them apart. They settle into an accretion disk. When there’s no material falling in, the quasar goes quiet.

Spectrum Width of line implies velocities of 30,000km/s ! High Orbital Speed implies deep gravitational well.

AGN Accretion Disk Simulations @ 0.1as Courtesy of Phil Armitage, U. Colorado and C. Reynolds, U. Maryland

Jets

Jets

Fields Twist to Make Narrow Jet

Radio Galaxies Very Large Array Very Large Baseline Array

Cygnus A

Radio Lobes Lobes contain 1053 Joules of energy in relativistic electrons. Mass energy equivalent of a million stars!

Wind Blows Jets

Full Model

Superluminal Expansion Radio interferometers see blobs emitted by AGN’s from base of jet. Watch them expand. Know distance, so can measure speed. v = 900,000km/s v = 3c Superluminal ! ? Is Einstein’s ghost worried?

Phase Velocity Point of impact can move v > c Nothing traveling that fast.

Better Explanation Blob moves close to speed of light toward us. Its closer later. Makes sideways motion appear speeded up.