Slide 1

Andromeda galaxy M31 Milky Way galaxy similar to M31

Slide 2 Fig. 15-10a, p.299

Model of Milky Way, diameter 100,000 lyCentral bulge radius 6,000 ly. Thickness of spiral arms 2,000 ly

Sun location is in spiral arm, 2/3 from the center to the edge

Nebula Globular cluster

Open cluster

Slide 3

Milky Way GalaxyMilky Way Galaxy• Size: diameter 100,000 ly, thickness of spiral arms

2,000 ly (2%). Radius of bulge ~ 5,000 ly• Contains 2 × 1011 stars. Mass 4 × 1011 M.• Nebula (~25% by mass), open clusters in spiral arms,

135 globular clusters in the galactic halo, central black hole has 2.6 × 106 solar masses.

• Velocity of rotation about 220 km/sec. • About half the mass is dark matter (matter that exerts

gravity, but is invisible).• Location of the Sun about 2/3 from center to edge in

spiral arm. Halfway in the thickness part of spiral arm.

Slide 4

GALAXIES

TYPES OF GALAXIES1. Spiral (Spiral Bar) 10%

Mass 0.1 to 10 times Milky Way

2. Elliptical 80%; Mass 0.001 to 50 Milky Way

3. Irregular 5% Mass < 0.01 Milky Way

4. Peculiar (active) – Radio galaxy, quasar, etc.

Slide 5

1. Elliptical galaxies: E0 to E7. E0 is spherical and E7 highly elliptical in shape. Contains very old, relatively less massive stars and have very little gas and dust. Most common galactic type.

2. Spiral galaxies: have central bulge and spiral arms. Have lots of gas and dust, mostly in the spiral arms. Spiral bar SB have a bar attached to central bulge.

3. Irregular galaxies: no particular shape but has lots of gas and dust. Typically smaller in mass than spiral galaxies. About few per cent of galaxies are irregular.

4. Active (peculiar) galaxies, such as quasars. Few in numbers.

Slide 6

Active (peculiar) Galaxies:Radio galaxies: Radio galaxies emit enormous amount of radio waves,

typically much farther than the corresponding optical galaxy. Radio galaxies usually are double lobed and have jets of particles emitted from the nucleus of the galaxy. When the jet of particles interacts with intergalactic matter, radio waves are created.

Quasars: Quasars are near the edge of the Universe. Very bright.Large redshift z > 0.1; small in size. Some give out enormous amount of radio waves.

Seyfert galaxies are somewhat between quasars and normal galaxies.Distance distribution of quasars tells us that the universe has an edge.From gravitational lensing of quasars by an in-between galaxy in our

line of sight, distances can be estimated and quasars are indeed very far away.

Most galaxies have supermassive black holes in their center. The larger the mass of the black hole, the larger is the central bulge

of the galaxy.

Slide 7 Fig. 17-2, p.344Radio galaxy Cygnus A Optical ^

Slide 8 Fig. 17-3, p.344

Slide 9 Fig. 17-4a, p.344Centaurus An elliptical galaxy-strong radio source

Slide 10 p.342

Quasar redshift z=0.17

Redshiftz = Δλ/λ

Slide 11 Fig. 17-4b, p.344

Centaurus A in X-ray

Slide 12 Fig. 17-13, p.350

Quasars – Size is small ~ 0.1 ly.

A large object can’t appear to fluctuate in brightness as rapidly as a smaller object. For example an object

abruptly brightens at one instant. The wave emitted from the edge of the object takes longer to reach the

observer than light from the near side of the object, because it has to travel farther. We don’t see the full

variation until waves from all parts of the object reach us.

Slide 13 Fig. 17-6, p.346

Four quasars. Quasars appeared star like (i.e. points) but withvery large Doppler shift. With bigger telescopes many quasarsnow have structure, such as spiral arms.

Slide 14 Fig. 17-11a, p.348

Next to most distant Quasar.Now largestz = 10

Slide 15 Fig. 17-14, p.351

Slide 16 Fig. 17-19, p.353

Quasar overexposedshows galaxy structure

Slide 17 Fig. 17-20a, p.353

Sloan Digital Sky Survey 2° FieldUniverse has an edge!

Slide 18 Fig. 17-20b, p.353

Universe has an edge.

Slide 19 Fig. 17-21, p.354

Interacting and colliding quasars

Slide 20 Fig. 17-23, p.355

NGC 4258has verybright center. A black hole

Slide 21 Fig. 17-24a, p.356

HST of M87.Galaxy nucleus is on top

Slide 22

M87Has a3×109M

Black Holein the center

Slide 23 Fig. 17-24b, p.356

M87 nucleus

Slide 24 Fig. 17-26b, p.357

Sagittarius A center of Milky WayVery small size and strong radio waves

Slide 25 Fig. 17-27, p.358The larger the central bulge, the more massive the black hole

Slide 26

Black Hole – mass 1 × 109 M

Slide 27 Fig. 17-30, p.360

Slide 28 Fig. 17-34, p.362

Slide 29 Fig. 17-33, p.361

Gravitational lensing of two quasars. Distance can be computed.

Slide 30 Fig. 17-33a, p.361

The two Quasarimagesare identical.Gravitationallensing.

Slide 31 Fig. 17-35a, p.362

Einstein ringfromgravitationallensing.

Slide 32

Summary

• Radio galaxies. Few in number, but enormous amount of radio energy emitted. The source of the radio waves is up to a million light years from the optical part.

• Quasars. Not all emit radio waves. Very compact (~0.1 ly), very bright compared to normal galaxies. Found near the edge of the Universe. Some have spiral arms.

• Seyferts. In between quasars and spiral galaxies.