Presentation on theme: "Slide 1 Andromeda galaxy M31Milky Way galaxy similar to M31."— Presentation transcript:
Slide 1 Andromeda galaxy M31Milky Way galaxy similar to M31
Slide 2Fig. 15-10a, p.299 Model of Milky Way, diameter 100,000 ly Central 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 Galaxy Size: diameter 100,000 ly, thickness of spiral arms 2,000 ly (2%). Radius of bulge ~ 5,000 ly Contains 2 × 10 11 stars. Mass 4 × 10 11 M . Nebula (~25% by mass), open clusters in spiral arms, 135 globular clusters in the galactic halo, central black hole has 2.6 × 10 6 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 GALAXIES 1.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 7Fig. 17-2, p.344 Radio galaxy Cygnus AOptical ^
Slide 12Fig. 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 13Fig. 17-6, p.346 Four quasars. Quasars appeared star like (i.e. points) but with very large Doppler shift. With bigger telescopes many quasars now have structure, such as spiral arms.
Slide 14Fig. 17-11a, p.348 Next to most distant Quasar. Now largest z = 10
Slide 29Fig. 17-33, p.361 Gravitational lensing of two quasars. Distance can be computed.
Slide 30Fig. 17-33a, p.361 The two Quasar images are identical. Gravitational lensing.
Slide 31Fig. 17-35a, p.362 Einstein ring from gravitational lensing.
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.