Galaxies
Galaxy Classification Spiral (S) Elliptical (E) Irregulars (Irr)
Normal Spirals Sa, Sb, Sc From a to c Bulge becomes smaller Arms less tightly wound
Barred Spirals SBa, SBb, SBc A to b to c similar to normal spirals. Arms at end of a bar passing though bulge.
Elliptical Galaxies E0, E1, E2, E3, E4, E5, E6, E7 From E0 to E7 Get more elliptical in shape Get fuzzy
Elliptical Galaxies Two types of elliptical galaxies, ‘ Dwarf elliptical galaxies orbiting M31 Giant elliptical galaxy at core of a galaxy cluster. Two types of elliptical galaxies, dwarfs and giants.
Irregular Galaxies Small size No defined shape fuzzy
Irregular Galaxies LMC SMC SMC and LMC are irregular galaxies orbiting the Milky Way.
Hubble Tuning Fork Diagram There is no observational evidence that this diagram shows galaxy evolution. NOTE: S0’s are spirals without arms.
S0 Class Look like E0’s Contain dust and gas like spiral galaxies. Therefore, they were named as S0’s.
Galaxy Clusters Galaxies tend to congregate into groups called galaxy These clusters can be small containing tens of galaxies or large containing hundreds or thousands of galaxies.
Galaxy Clusters The Local Group Small cluster to which the Milky Way belongs. ~ 1,000,000 pc in diameter. Contains ~45 members. Andromeda Galaxy ~2.2 million LY away.
Galaxy Clusters The Virgo Cluster 18 Mpc 2500 galaxies M87, the central galaxy (giant elliptical) Local Group may be like an appendage to the Virgo Cluster. Super Clusters
Active Galactic Nuclei (AGN’s) ~20-25% of bright galaxies are not normal (do not fit Hubble classifications.) Among the most energetic object in the universe. Have bright nucleus NGC 7742 looks like a fried egg.
Types of AGN’s Seyfert Galaxies Radio Galaxies Quasars
Seyfert Galaxies Very bright central nucleus Faint spiral arms Variable in brightness
Seyfert Galaxies Nucleus changes brightness Time scales of weeks, months, and years. PEGA at GSU has observed AGN microvariblility on time scales of minutes.
Radio Galaxies Large radio emitting lobes Lobes extend out 10X larger than Milky Way or ~ size of The Local Group.
Radio Galaxies
M87
Cygnus A Colliding Galaxies
M86 Also near center of Virgo Cluster Core-dominated radio galaxy
Quasars Tiny blue stellar looking objects with large radio emission similar to radio galaxies. Highly red shifted spectra. ~ 50,000 km/s or more.
Quasars Quasar means quasi-stellar object. Distances from 240 Mpc to 9000 Mpc They are the brightest thing in universe but appear faint
Quasars They share characteristics of Seyfert galaxies and radio galaxies. Over 30,000 known
AGN Model Super massive black hole at center. Accretion disk Intense magneitc field Jets of high speed particles.
AGN Model
AGN Model Viewing angle determines type of energy seen. Viewing angle determines the type of AGN seen, Seyfert, radio galaxy, etc.
Possible Galaxy Evolution
Resources Chaisson & McMillan, (2002, 2004). Astronomy Today (5th Ed.)