Galaxies

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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
f

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
LMC
SMC
SMC and LMC are irregular galaxies orbiting the
Milky Way.
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Hubble Tuning Fork Diagram
There is no observational evidence that this
diagram shows galaxy evolution. NOTE S0s are
spirals without arms.
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S0 Class

• Look like E0s
• Contain dust and gas like spiral galaxies.
• Therefore, they were named as S0s.

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Galaxy Clusters
Galaxies tend to congregate into groups called
galaxy clusters. These clusters can be
small containing 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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What is our place in the universe?
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Active Galactic Nuclei (AGNs)

• 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 AGNs

• 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 observed AGN 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.)