Lecture 21: Active Galaxies and Quasers- Beacons of High Energy

"Long ago, in a galaxy far away..."
Star Wars

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Date: April 18, 1995
Reading Assignment: pp. 566-590

Description : Quasars, AGN, and active galaxies

Objectives

be able describe why active galaxies are considered different from normal galaxies

be able to describe Seyfert, Core-Halo, and Lobe radio galaxies

be able to describe the central regions of a radio galaxy where most of the energy is being produced

be able to compare the differences and similarities between radio galaxies and quasars

Lecture Outline

Slide # 1: Active Galaxies Slide # 2: Today's Lecture

normal galaxy review

classes and star formation

distance ladder

hubble's law

active galaxies

observations

models

quasars

Slide # 3: Cepheid Variables

very high luminosity stars

found in globular clusters

by measuring the period, you can find the luminosity

from the luminosity and the brightness, you can calculate the distance

Slide # 4: The Hubble Classification Scheme

spirals

barred spirals

ellipticals

irregulars

Slide # 5: Hubble Types (GRAPHICS)

Hubble classification scheme

Slide # 6: Star Formation and Galaxies

spirals and barred spirals have moderate rates of star formation

ellipticals and S0's have essentially no on-going star formation

irregulars have variable amounts of star formation

may be very high or very low

Slide # 7: Star Formation Rate

the number of stars forming at any given time

depends on the type of galaxy

Slide # 8: Star Formation Rates (GRAPHICS)

elliptical, spiral, and irregular galaxies

Slide # 9: Evolution of Galaxies

do spirals evolve from ellipticals?

do spirals arms and bulges change?

what are irregular galaxies?

Slide # 10: The Distance Ladder

to measure the distance to galaxies, you need to use several steps

you cannot measure distances to galaxies directly

Slide # 11: Standard Candles

used in many stages of the distance ladder

assumes that something has a known absolute magnitude

Slide # 12: Cepheid Variables

bright variable stars

period of pulsation is related to absolute magnitude

a bright standard candle which is easy to identify

can be used for globular clusters and nearby galaxies

Slide # 13: Type Ia Supernova Explosions

very bright explosions

can be identified from spectra and light curve

luminosity, so they work as a standard candle

Slide # 14: The Tully-Fisher Relationship

rotation speed related to mass

mass related to luminosity

so--- rotation speed related to luminosity

galaxies can be used as "standard candles"

Slide # 15: The Distance Ladder

radar

parallax

spectroscopic parallax

Cepheid variables

type I supernova, Tully-Fisher

Slide # 16: Hubble's Law

1912- Slipher discovered most spiral nebula are receding from us

1920's- Hubble discovered that the speed of recession is proportional to the d

Slide # 17: Hubble's Law (GRAPHICS)

distant galaxies receed rapidly

the greater the distance, the more rapid the recession

Slide # 18: Hubble's Law (GRAPHICS)

recessional velocity vs distance

Slide # 19: Hubble's Law (GRAPHICS)

H is the Hubble constant

H = 80 km/s/Mpc

Slide # 20: The Hubble Constant - H

very difficult to accurately determine

current values range from 50 to 100 km/s/Mpc

determining H is one of the main missions of Hubble Space Telescope

Slide # 21: What does it mean?

Hubble's law was discovered with observational data

not a theoretical prediction

it can be used to determine the distance to galaxies

measure the recessional velocity, and calculate distance

Slide # 22: Constellation Corner (GRAPHICS)

Constellation De Jour

Slide # 23: Northern VA Astronomy Club

3rd Wed of the Month - 7:30 pm

Arlington Planetarium

Slide # 24: Scorpius (GRAPHICS)

July 4 - 11pm - South - 4.0

Slide # 25: Scorpius (GRAPHICS)

July 4 - 11pm - South - 4.0

Slide # 26: Star Maps (GRAPHICS)

April 18- midnight- 4.0

Slide # 27: Hercules (GRAPHICS)

April 18- Midnight- W - 4.0

Slide # 28: Hercules (GRAPHICS)

April 18- Midnight- W - 4.0

Slide # 29: Leo (GRAPHICS)

April 18 - Midnight - West - 4.0

Slide # 30: Leo (GRAPHICS)

April 18 - Midnight - West - 4.0

Slide # 31: Clusters of Galaxies (GRAPHICS)

center of the Virgo Cluster

Slide # 32: Active Galaxies

the centers of some galaxies are producing HUGE amounts of energy

about 5% of galaxies

these are active galaxies

they contain active galactic nuclei

Slide # 33: Spectra of Active Galaxies (GRAPHICS)

active galaxies emit much more radio energy

Slide # 34: Energy Output

Milky Way Galaxy = 1044 erg/s

Most energetic normal galaxy = 1045 erg/s

Active Galaxies = 1043 to 1049 erg/s

up to 100,00 times more luminosity than the Milky Way!

Slide # 35: Types of Active Galaxies

Seyfert Galaxies

Radio Galaxies

Radio Lobe

Core-Halo Galaxies

Slide # 36: Seyfert Galaxies

spiral galaxies with very bright nuclei

appear to be normal in longer exposures

the nuclei vary in brightness

brightness changes by factor of two in a few months

Seyfert spectral lines are unusual

strong emission lines from ionized heavy elements

very broad lines indicating high temp or rapid rotation

Slide # 37: Rapid Variation (GRAPHICS)

time it takes for brightness to vary is related to its size

Slide # 38: Rapid Variation

if something varies it brightness in a few months, it must be less than a few

Seyfert nuclei are MUCH smaller than galaxies

Slide # 39: Radio Galaxies

core-halo galaxies

radio lobe galaxies

Slide # 40: Core-Halo Galaxies (GRAPHICS)

most radio energy in the core

some in a surrounding radio halo

Slide # 41: Radio Lobe Galaxies (GRAPHICS)

most energy in "lobes" of radio energy around the core

energy = 10 times more than the Milky Way

Slide # 42: Summary of Observations

very high luminosity

nonstellar spectra

highly variable over short time periods

often have jet-like structures

emissions lines are very broad

Slide # 43: Interpretation

lots of energy created in a small area

can't be stars- wrong spectra

must be strong gravity

spectral lines are broad indicating rapid rotation

jets may be from an accretion disk

Slide # 44: Accretion Disks (GRAPHICS)

material falling on a compact object emits energy from its accretion disk

Slide # 45: Big Accretion Disks

AGN's are powered by accretion disk

like a binary star, but MUCH bigger

the center is probably a supermassive black hole

108 to 1010 solar masses!!!!

Slide # 46: Supermassive Black Holes

fits all the observations

new evidence from Hubble Space Telescope

very rapid rotation within a few parsecs of the nucleus

using Newtonian gravity, it can only be a black hole

Slide # 47: Quasars

QUAsi-Stellar Radio Source

optical object associated with a strong radio source

star-like objects with unusual spectra

1960's - found QSO have very large redshifts

Slide # 48: Quasars- observations

very high large redshift

very small angular size

varies in brightness in a few weeks

evidence for gravitational lensing in a few cases

duplicate images of the "same" quasar

Slide # 49: Large Redshift

Hubble's law implies these are VERY far away

10 billion light years

look-back time says these were more common in the early universe

few billion years after big bang

quasars are VERY luminous

Slide # 50: A New Debate

what is the nature of Gamma-Ray bursts

are they inside or outside our Galaxy?

A Debate on April 22 at the Natural Hisotry Museum

Lamb vs Paczynski