Hubble Expansion

1
Hubble Expansion
2
Satellite Galaxies

• The Milky Way has 200 billion stars and a large
  gravitational force.
• The Magellanic Clouds are irregular galaxies that
  orbit the Milky Way.
• There are 9 dwarf galaxies within 500,000 ly.

3
Local Group

• The nearest large galaxy is M31 in Andromeda.
• Together with satellites the Milky Way, M31, and
  the Triangulum Galaxy make up the Local Group.
• This group is 10 million ly across with 700
  billion stars.

4
Virgo Cluster

• The Virgo Cluster includes more than 2000
  galaxies.
• They all exert gravity on each other.
• X-ray views show the collisions of gas and dust.

visible
x-ray
5
Supercluster

• The Local Group orbits the massive Virgo Cluster.
• Many clusters make up the Virgo Supercluster.

6
Hubbles Law

• Most all galaxies are moving away from us.
• Not expected 100 years ago
• Distant galaxies move fastest
• Hubble found a simple relationship between
  distance and velocity.
• Hubbles Law

• v H0 d Hubbles Law
• v recessional velocity
• d distance
• H0 1.5 to 3.1 ? 10-18 per sec
• Hubble constant

7
Galactic Luminosity

• The distribution of luminosity in galaxies in a
  cluster is relatively consistent.

8
Luminosity Fit

• An approximate analytical form is used to fit
  luminosities in a cluster.
• Density of galaxies F
• Range from L to LdL
• Normalization F
• There is a characteristic luminosity L where the
  slope changes rapidly.

9
Distant Light

• Some objects in deep space are visible, small,
  and have large redshifts.
• Hubbles law suggests that these objects are very
  distant.
• Some are billions of light years away.

larger wavelength
nearby galaxy
distant object
10
Expanding Universe

• Hubbles law suggests that the galaxies in the
  universe are spreading out over time.
• From Einsteins general relativity this happens
  as space itself expands.
• The dimensional scale increases as the universe
  expands.

11
Stretching Light

• As the universe expands the wavelength of light
  stretches.
• At the burst of light, 3000 K.
• Peak radiation was 1 micron.
• This is visible light.
• The universe is 1000 times larger.
• The temperature is 3 K.
• The peak radiation is 1 mm.
• These are microwaves.

1 wavelength, small universe
1 wavelength, expanded universe
12
Quasi-Stellar Objects

• Some distant objects were first observed as
  intense radio sources.
• They were star-sized, but too bright.
• They were named quasi-stellar radio
  sourcesquasars.

13
Distant Past

• Looking at a faraway object is equivalent to
  looking back in time.
• If a quasar is 5 billion ly away, we are seeing
  the universe 5 billion years ago.

Andromeda 2 million years ago
Earth
PKS 1127 4 billion years ago
14
Energy Release

• Quasars emit in all parts of the electromagnetic
  spectrum.
• Many shine with the light of 100 galaxies.
• Quasars can flare up to 10,000 times the light of
  a galaxy.

3C279, a quasar photographed in gamma rays
15
Disk and Jets

• Radio measurements show two giant jets of
  radiating gas.
• Visible light and x-rays see a disk of gas, dust
  and stars.
• The most intense radiation is from a small area
  at the center.

16
Jet Formation

• Quasars form from a supermassive black hole.
• The black hole draws stars and dust to its
  center.
• The material is accelerated to high velocity and
  ejected out either side.

17
Early Galaxies

• Supermassive black holes are observed in most
  galaxies.
• All quasars have large redshifts.
• Very far away
• Early universe
• Quasars may be consistent with early galaxies.

18
Active Nuclei

• Some nearby galaxies show jets of radiating gas.
• AGN Active galactic nuclei
• The jets are consistent with a supermassive black
  hole.

19
Radio Galaxies

• Visible elliptical galaxies have black holes in
  their center.
• The jets are only seen with radio telescopes.
• These are called radio galaxies.

20
Galactic Evolution

• Astronomers believe that large galaxies form
  quasars.
• As the early dust is used up the quasar fades.
• The galaxies are active as additional matter is
  consumed.

21
Colliding Black Holes

• The Chandra X-ray Observatory has observed two
  supermassive black holes in the same galaxy.
• The galaxy NGC 6240 is 400 million light years
  away.
• When the holes collide in a few hundred million
  years, the gravity waves will be felt on earth.