Spiral Galaxies
Ron Buta
University of Alabama
What are spiral galaxies?
Flattened systems of stars, gas, and dust stars seem to concentrate in spiral “arms” all bound by gravity into a single unit typical size:50,000-100,000 light years typical mass: 10billion-500billion suns often there is also a prominent bulge
Face-on spiral galaxy
Highly inclined spiral galaxy
Edge-on spiral galaxy
Edge-on Spiral Galaxy
Why are spirals interesting?
An intriguing morphology difficult to explain common and widespread thoughout the
Universe new stars tend to form in spirals but not in
other types of galaxies part of process of galaxy evolution and
interaction our Galaxy is a spiral
Discovery of Spirals
1845 William Parsons, Third Earl of Rosse, Ireland
72-inch reflector visually detected spiral arms in the
Whirlpool Nebula M51 many other “nebulae” found to be spirals
William Parsons, “Lord Rosse” 1800-1867
Discovery of spiral structure in M51
What causes spiral structure?
Natural phenomenon in flat, rotating stellar disks
possibly triggered by an interaction with another galaxy
or generated by bars “density waves”
Spiral galaxy research at UA
morphology sense of winding of spiral arms gravitational torques due to bars and spiral
arms star formation in galactic rings
The de Vaucouleurs Atlas of GalaxiesGerard de Vaucouleurs 1918-1995
The de Vaucouleurs Atlas: what is it?
Authors: R. J. Buta (U. Alabama) H. G. Corwin, Jr. (Caltech) S. C. Odewahn (U. Arizona) publisher: Cambridge Univ. Press Purpose: to illustrate the de Vaucouleurs
revised Hubble classification system with modern digital images
NGC 7457 SA(rs)0-
NGC 1553 SA( r )0
NGC 1291 (R)SB(s)0/a
NGC 2713 (R’)SB(rs)ab
NGC 4736 (R)SA( r )ab
NGC 5850 SB( r )b
NGC 4501 (M88) SA(rs)b
NGC 4321 (M100) SAB(s)bc
NGC 1566 SAB(s)bc
NGC 6643 SA(rs)c
NGC 7479 SB(s)c
NGC 6946 SAB(rs)cd
NGC 5585 SAB(s)d
NGC 4618 SB(rs)m
Sense of winding of spiral arms
Trailing arms: follow direction of rotation Leading arms: oppose direction of rotation most spiral arms trail but one galaxy has leading arms!
Trailing arm spiral M81
Leading arm spiral galaxy NGC 4622
Barred spiral galaxies
A bar-like pattern of old stars crosses the center
arms break from the ends of this bar 70% of spirals have a bar, including the
Milky Way
Barred spiral galaxy NGC 1365
Barred spiral NGC 1300
How stars move in presence of a bar
In solar system, planets follow elliptical paths with Sun at one focus
no torque on planet as it orbits in presence of a bar, star may follow a
centered elliptical orbit there is a torque on star as it orbits amount of torque is a measure of “bar
strength”
Rings of Star Formation
Real bar orbit “lit up” by new stars often not circular
Gallery of spirals from the Hubble Space Telescope
Typical spiral galaxy: NGC 4414
Starburst spiral galaxy NGC 3310
Ringed spiral galaxy NGC 7742
Superposed spiral galaxies NGC 3314
Edge-on spiral galaxy ESO 510-13
Edge-on spiral galaxy NGC 4013
Peculiar ring galaxy: Hoag’s Object
Barred spiral galaxy NGC 4319 with quasar
Polar ring galaxy NGC 4650A
Compact galaxy group
Colliding spiral galaxies: NGC 6745
The Spiral Menagerie: Visual Observations of Spirals from McDonald and Siding Spring
Observatories
1977-1984 photoelectric galaxy photometry runs McDonald 30, 36, 82, and 107-inch
telescopes Siding Spring 40-inch telescope
NGC 5194-5 (M51) - McDonald 30-inch
NGC 1566, SSO 40-inch
NGC 2403, McD 30-inch
NGC 3034 (M82), McD 36-inch
NGC 3893(36McD), 4449(36McD), 4676(107McD), 3646(36McD), and 5921(36McD)
NGC 4631 (left) and NGC 4565(right) (both 30McD)
M99, M100, M88, and M61 (all 30McD)
M77(36McD), NGC4535(30McD), NGC5394-5(36McD), NGC3395-6(36McD), NGC5426-7(36McD), NGC5247(36McD)
Thank you!