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>.