AST101 The Evolution of Galaxies

Virgo Cluster

Collisions of Galaxies Outside of Clusters (the field), most galaxies are spiral or irregular In dense clusters, the most massive galaxies are ellipticals Spirals in clusters tend to inhabit the periphery

Formation of Galaxies Initially: masses ~ 10 6 M  Protogalaxies collided and merged to form larger galaxies. If there is a net angular momentum, a disk forms, giving a spiral galaxy

Arp 220 the Antennae

NGC 2207

Collisions Today The Sagittarius Dwarf galaxy

Active Galactic Nuclei The center of the Milky Way is a 2x10 6 M  black hole. Bigger galaxies have more massive central black holes (up to 10 9 M  ) Some just sit there Others are actively accreting matter (gas, stars)

Active Galactic Nuclei Accretion proceeds through a disk Accreting gas orbits near the Schwarzchild radius (event horizon) of the black hole The gas heats up as potential energy is converted to kinetic energy (heat) We see bright X-ray sources

M87 Virgo Cluster

Relativistic Jets Accreting black holes emit jets of radiation at velocities near the speed of light Radio Jet: M87

Radio Galaxies  Cygnus A  Centaurus A

Quasars In 1963 Martin Schmidt puzzled over the spectrum of a 12 th magnitude star- like radio source (a quasi-stellar object, or QSO)

3C 273 Redshift z = 0.16; Distance 2.4 x 10 9 ly It is one of the most luminous objects in the universe

Active Galactic Nuclei Quasars Blazars Liners Seyfert galaxies All involve matter infall into massive black holes.