Spiral Galaxies

Elliptical Galaxies

Irregular Galaxies

Classification of Galaxies

Properties of Galaxies SpiralsEllipticalsIrregulars Mass [typical; range] (solar masses) ; ; ; Size (pc) ColorBlue arms, reddish bulge reddishbluish Luminosity Stellar PopulationsPops I & IIPop IIPop I (Pop II) Interstellar mediumYesVery littleStill some RotationYes (disk)noNot a lot Fraction30%20%50% Other galaxy types : Peculiar, Interacting, Ring, Starburst, Dwarf, Luminous Infrared, Active Nuclei, Damped Lyman-alpha

Stephan’s Quintet – Colliding galaxies

The “Anntenae” Galaxies – a case study

Ring Galaxies – the “splash” Head-on collisions can produce a “ripple” of star formation that expands outwards.

Galactic Superwinds

The Magellanic Clouds Large Magellanic Cloud Small Magellanic Cloud Southern Hemisphere only These are the nearest irregular galaxies. There are others even closer, being torn apart by our Galaxy (last discovery: 2003 in Canis Major).

Our Immediate Galactic Neighborhood

Members of the Local Group

M31 vs Milky Way Before the Sun dies, we may collide and merge with the Andromeda Galaxy… (not quite sure yet about this)

Collisional Aftermath

And outward…

Galaxy Clusters Virgo Coma Notice the giant ellipticals at the centers of many clusters. These are an example of “galactic cannibalism”.

Galactic Cannibals – Central CD Ellipticals At the heart of rich clusters, galaxies pass through the center and are disrupted and collected.

Making a CD galaxy

The Core of M87 (at the center of Virgo)

Giant Radio Lobes Many such jets are seen. If they last long enough, they can blast out of the galaxy for millions of light years: the largest single coherent objects in the universe.

Seyfert Galaxies Increasing exposure times…. Some galaxies have unusually bright nuclei…

Quasars (Quasi-stellar Objects) QSO Star Strange “stars” were found with spectral lines that turned out to be normal lines but at extremely high red Doppler shifts. The expansion of the Universe means that they must be VERY far away, yet they were not too faint. Even Seyfert nuclei would not be bright enough. The energy output would have to be up to 100’s of times that from a whole normal galaxy, but the source was point-like.

Host Galaxies of Quasars Finally, we were able to obtain deep images of quasars, and show that indeed they are extremely bright galactic nuclei. The only power source that is adequate is a supermassive black hole, eating up to several solar masses per year.

Supermassive Black Holes You know the Milky Way has a 3 million solar mass BH at its center. Are they common? Bigger? Centaurus A Luminosities seem to require them. How could we prove the theory? A billion solar-mass black hole is still only the size of the solar system.

Measuring the Monster’s Mass

Images of Active Galaxy disks Recently, the theory of AGN has received spectacular visual confirmation from the Hubble Space Telescope.

Unification of Active Galactic Nuclei Depending on what the viewing angle is, what we see can be rather different. This is now sorted out.

into the Universe…

Large Scale Structure On the largest scales (100 million ly) the Universe takes on a “foamy” appearance, with great filaments and walls of galaxies and clusters, surrounding great “voids” that are relatively empty.