galaxies. galaxy classification spiral (s) elliptical (e) irregulars (irr)
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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
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
SMC and LMC are irregular galaxies orbiting the Milky Way.
LMCSMC
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 congregateinto groups called galaxy clusters.
These clusters can be smallcontaining tens of galaxies or large containing hundreds or thousands of galaxies.
Galaxy ClustersThe 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 ClustersThe 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 observedAGN 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 AColliding 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.)