AST101 The Evolution of Galaxies. Virgo Cluster Collisions of Galaxies Outside of Clusters (the field), most galaxies are spiral or irregular In dense.

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 ~ 106 M

• Protogalaxies collided and merged to form larger galaxies.

• If there is a net angular momentum, a disk forms, giving a spiral galaxy

Arp 220the Antennae

NGC 2207

Collisions Today

The Sagittarius Dwarf galaxy

Active Galactic Nuclei

• The center of the Milky Way is a 2x106 M black hole.

• Bigger galaxies have more massive central black holes (up to 109 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

M87Virgo 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 12th magnitude star-like radio source (a quasi-stellar object, or QSO)

3C 273• Redshift z = 0.16; Distance 2.4 x 109 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.