galaxies. galaxy classification spiral (s) elliptical (e) irregulars (irr)
TRANSCRIPT
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Galaxies
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Galaxy Classification
• Spiral (S)• Elliptical (E)• Irregulars (Irr)
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Normal Spirals
• Sa, Sb, Sc• From a to c
– Bulge becomes smaller– Arms less tightly wound
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Barred Spirals
• SBa, SBb, SBc• A to b to c similar to normal spirals.• Arms at end of a bar passing though bulge.
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Elliptical Galaxies
• E0, E1, E2, E3, E4, E5, E6, E7• From E0 to E7
– Get more elliptical in shape– Get fuzzy
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Elliptical Galaxies
Dwarf elliptical galaxies orbiting M31
Giant elliptical galaxy at core of a galaxy cluster.Two types of elliptical galaxies,
dwarfs and giants.
‘
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Irregular Galaxies
• Small size• No defined
shape• fuzzy
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Irregular Galaxies
SMC and LMC are irregular galaxies orbiting the Milky Way.
LMCSMC
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Hubble Tuning Fork Diagram
There is no observational evidence that this diagram shows galaxy evolution.
NOTE: S0’s are spirals without arms.
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S0 Class
• Look like E0’s• Contain dust
and gas like spiral galaxies.
• Therefore, they were named as S0’s.
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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.
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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.
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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
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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.
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Types of AGN’s
• Seyfert Galaxies
• Radio Galaxies
• Quasars
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Seyfert Galaxies
• Very bright central nucleus
• Faint spiral arms• Variable in brightness
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Seyfert Galaxies
• Nucleus changes brightness
• Time scales of weeks, months, and years.
PEGA at GSU has observedAGN microvariblility on time scales of minutes.
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Radio Galaxies
• Large radio emitting lobes• Lobes extend out 10X larger than Milky Way or
~ size of The Local Group.
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Radio Galaxies
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M87
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Cygnus AColliding Galaxies
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M86
• Also near center of Virgo Cluster
• Core-dominated radio galaxy
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Quasars
• Tiny blue stellar looking objects with large radio emission similar to radio galaxies.
• Highly red shifted spectra.
• ~ 50,000 km/s or more.
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Quasars
• Quasar means quasi-stellar object.
• Distances from 240 Mpc to 9000 Mpc
• They are the brightest thing in universe but appear faint
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Quasars
• They share characteristics of Seyfert galaxies and radio galaxies.
• Over 30,000 known
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AGN Model
• Super massive black hole at center.
• Accretion disk• Intense magneitc field• Jets of high speed
particles.
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AGN Model
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AGN Model
• Viewing angle determines type of energy seen.
• Viewing angle determines the type of AGN seen, Seyfert, radio galaxy, etc.
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Possible Galaxy Evolution
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Resources
Chaisson & McMillan, (2002, 2004). Astronomy Today (5th Ed.)