GalaxiesPart 2

Dr. Bill Pezzaglia

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Updated: Nov 27, 2012

Messier Catalog 2

Charles Messier (1730-1817) was hunting for comets. People kept reporting the same fuzzy blobs that were NOT comets, so from 1758-1782 he made a catalog of about 100 of these fuzzy things to “ignore”.

In fact, these 110 objects are nebulae, star clusters and galaxies, which are the best things to look for in an amateur telescope!

e.g. “M31” is the Andromeda Galaxy

Some Galaxies in Messier Catalog 3 William Herschel 4

• 1785 Catalog of 1000 objects• 1788 another 1000 objects• 1802 another 500 objects

Classifies objects into star clusters and nebulae. The “types” were:

1. Bright Nebulae 2. Faint Nebulae 3. Very faint Nebulae 4. Planetary Nebulae 5. Very large Nebulae 6. Very compressed and rich star clusters 7. Compressed clusters of small and large (i.e.,

faint and bright) stars 8. Coarsely scattered clusters of stars

Herschel sees more (galaxies) 5 NGC: New Galactic Catalog 6

• 1864 Herschel’s son John publishes the “GC”, Galactic Catalog of 5079 objects.

• 1888 J. L. E. Dreyer publishes the “New Galactic Catalog” for use in Lord Rosse’sobservatory (the 72” Leviathan Telescope). It will take 45 years for people to realize the “spiral nebulae” seen by Lord Rosse are in fact galaxies.

C. Galaxy Structure & Evolution 7

1. Hubble Classification

2. Active Galaxies

3. Galactic Evolution

Edwin Hubble (1889-1953) 8

• 1919 invited to Mount Wilson Observatory

• 1925 publishes work that supports idea of existence of galaxies.

• Develops classification scheme for galaxy types• Elliptical• Spiral• Irregular

C1a. Hubble’s Tuning Fork 9 C1b. Elliptical Galaxies 10

M87 Type E0Giant Elliptical in Virgo

M87, Elliptical in Virgo Cluster 11 M87 Giant Elliptical (Virgo) 12

Type: E0, perhaps 3 trillion stars! (largest known)

No spiral arms, so no new star formation!

C1c. Spiral Galaxies 13

NormalSpirals

BarredSpirals

M74 (NGC 628, Pisces) 14

“Grand Design” spiral

NGC 4414 (Coma Berenices) 15

Flocculent (“wooly”) spiral galaxies are opposite of “grand design”. The arms are not very distinct.

M61 (Virgo) 16

Type Sb

Andromeda Galaxy (M31)

2.5 million light years away!

Type: Normal Spiral Sb

17 NGC 1300 (Eridanus)Type: Barred Spiral (Hubble SBc)21 MPC away (discovered by Herschel 1835)

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Seyfert Galaxy NGC 7742Spiral with Ring (Black Hole in center?)

19 Galaxies in Leo 20

Two Clusters

M95 & M96 (Leo) 21

Two spirals, 34 million light years away

M95 (Leo) 22

Barred Spiral

M66 (Leo) 23

Part of Leo Triplet (M65, M66, NGC 3628)

The spiral structure of M66 is interesting as it sh ows strong deformations through gravitational interaction with neighboring galaxies, especially M65. This is particularly noticeable in the western spir al arm (top in this image) which appears to be separated and rising above the main galaxy.

M104: Sombrero Galaxy 24

Type: Sa

25M104: Sombrero Galaxy

1990: motion of stars near center imply a billion solar mass black hole!

C1e. Edge-On Spirals 26

Edge on Spirals show usthere is a lot of dust/gasin the galactic planes

NGC 5866 (Type S0 Edge-on) 27

Spindle Galaxy

Galaxies in Ursa Major 28

29M81 Bode’s GalaxyGrand Design Spiral Galaxy type Sa in Ursa Major

M101 Pinwheel (Ursa Major) 30

Type Sc, “Grand Design” spiral

2. Active Galaxies 31

a) Starburst Galaxiesb) Radio Galaxies

c) Quasars

Cigar Galaxy (M82), LMC and SMC are examples of Irregular Galaxies. Only 3 % of galaxies are of type Irr

C2a1. Irregular Galaxy M82

Type: Irr (pec)“peculiar”StarbustGalaxy

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While M81 & M82 seem separate,

actually they are connected by H gas.

M81’s gravity disrupted M82

causing a starburst formation

C2a2. Galaxies are Connected 33 C2b1. M87, a Giant E0 (pec) 34

The radio jet coming out of M87 is probably due to a supermassiveblack hole

C2b2. Centaurus A an “active”radio galaxy

35 C2c1. Quasars (Quasi Stellar Object) 36

• First one discovered was 3C273• Very big redshift, hence far away, hence VERY

BRIGHT, but mystery was its very small in size• Recent Chandra data shows X-Ray jet of material,

consistent with Black Hole• Model: early form of galaxy, with black hole formi ng.

http://chandra.harvard.edu/photo/2000/0131/

C2c2. Quasars/Radio Galaxies same? 37 3. Galaxy Evolution 38

a) Galactic Birthb) Collisions

c) Mergers

C3a. Galactic Formation: a mystery! 39 I Zwicky 18: A young galaxy 40

An Irregular galaxy only 45 million light years away, appearsTo be only 500 million years old!

C3b1. The Antennae

Generically classified as “Rat Tail Galaxies”

41 C3b3. Galaxy Collisions 42

“Rat Tail” galaxies are probably formed by collisions

AM 0644-741

Probably collision punched out the center of the galaxy

C3b2. Ring Galaxies 43 Hoag's Object (Ring Galaxy) 44

M64 Blackeye Galaxy 45

In Coma Berenices groupC3c. Black Eye Galaxy M64

Type Sb (pec)The dark gas is revolving in the opposite direction as the stars. This is possibly due to the galaxy gobbling up a smaller satellite galaxy 1 billion years ago.

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M51 Whirlpool Galaxy 47

The blob on the right is a small galaxy that collided

References/Notes 48

•Quasar: http://en.wikipedia.org/wiki/3C_273•http://www.skyimagelab.com/galaxies.html•http://en.wikipedia.org/wiki/List_of_galaxies

Things to do 49

•More on local group of galaxies•Need to add “radio astronomy” here, active galaxies•More on lookback time•In 1944, Hendrik van de Hulst predicted microwave radiation at a wavelength of 21 cm, resulting from interstellar atomic hydrogen gas; this radiation was observed in 1951

•How BIG is a supermassive black hole?