CLASSIFYING GALAXIES
By: Mary Lange
EDWIN HUBBLE November 20, 1889 – September 28, 1953 An American astronomer Confirmed other galaxies existed The first to categorize galaxies
HUBBLE’S GALAXY CLASSIFICATIONThe 3 Major Galaxy Classifications
Spirals Elliptical Irregulars
SPIRAL GALAXIES Flattened galactic
disk Spiral arms
Central galactic bulge Dense nucleus
Extended halo Faint, Old stars
Newer Stars
Example: Milky Way Galaxy Andromeda
ELLIPTICAL GALAXIES No galactic disk
No spiral arms
Little or no bulge Dense central
nucleus
No halo
Less evidence for young stars
IRREGULAR GALAXIES Do not fit into any
other category!
Rich in interstellar matter
Young Blue Stars
Lack Regular Structure
THE TUNING FORK OF HUBBLE SEQUENCE
This image shows how similar in appearance the galaxies appear to be.
E0- E7 are elliptical galaxies SO are between the elliptical and spiral S and SB are spiral galaxies
Sa – Sc are spiral galaxies SBa – SBc are barred-spiral
Elliptical Galaxies
No Disk- stars distributed though ellipsoidal volume
Contain only old stars, no significant star formation in last 10 billion years
Early type galaxies
Stars have random orbits
Spiral Galaxies
Flattened disk of stars and gas, contains spiral arms
Contains young and old stars with Ongoing star formation
Late type galaxies
Stars move in circular orbit around galactic center
BRIGHT GALAXIES Seyfert Galaxy
Discovered by Carl Seyfert in 1943. Resemble the “Normal Galaxy” All Energy is emitted from the galactic nucleus. 10,000 times brighter than our galaxy.
BRIGHT GALAXIES Radio Galaxy
Radio galaxies are in the elliptical family. Emits energy from it’s lobes. Differs from the Seyfert Galaxies
The wavelengths at which they radiate Appearance Emitting regions (Radio portion of the electromagnetic
spectrum)
BRIGHT GALAXY Quasar Galaxy
Date back to much earlier periods of galaxy formation and evolution than other galaxies.
Share many properties of Seyferts and Radio Galaxies Most energy is emitted in infrared spectrum Jets and extended emissions
REFERENCES Ewert, Michael. Astronomy 162. N.p.: University of Tennesse,
n.d. N. pag. Web. 6 Dec. 2011. <http://csep10.phys.utk.edu/astr162/lect/index.html>.
McMillan, Steve, and Eric Chaisson. Astronomy: A beginner's guide to the universe. sixth ed. San Francisco: Addison-Wesley, 2010. 404-29. Print.
Ventrudo, Brian. One Minute Astronomer. N.p.: Brian Ventrudo, Ph.D., 2011. Web. 6 Dec. 2011. <http://www.oneminuteastronomer.com>.
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