Types of Galaxies

Barred Spiral

Elliptical Irregular

LenticularSpiral

Deep Sky Catalogs• Messier Catalog

• Charles Messier, 1781• 110 objects (40 galaxies)

• New General Catalog (NGC)• JLE Dreyer, 1888• 7840 objects

Messier Objects

Spiral Galaxies(face on)

NGC 1357 M81Bode’s Galaxy NGC 4321

Sa ScSb

Spiral Galaxies(edge on)

M104Sombrero Galaxy NGC 891 NGC 4631

Herring Galaxy

Sa ScSb

Spiral Galaxiesvariety of spiral arms

M74

Poorly defined spiral arms

M33Triangulum Galaxy

Well defined spiral arms

The Winding Dilemma

Density Waves

Barred Spiral Galaxies

NGC 4650 M83Southern Pinwheel

Galaxy

NGC 1365

SBa SBcSBb

Lenticular Galaxieslack spiral arms

M102

S0

Elliptical Galaxies

M105 M49

E1 E5E4

M59

Elliptical Galaxies

Virgo clusterM84 (right) and M86 (left)over 2 million ly diameter

Giant Elliptical Galaxies Dwarf Elliptical Galaxy

Leo I(type E4)

3000 ly diameter

Hubble’s Classification Scheme

Irregular Galaxies

Large Magellanic Cloud(LMC)

NGC 4485 (top)NGC 4490 (bottom)

Structure in the Universe

Galaxy Clusters

Virgo cluster Fornax cluster

Galaxy Clusters

Hercules cluster

The Local Group

Galactic Collisions

NGC 4676“The Mice” BGC 2207 and IC 2163

Galactic Collisions

M81

M82

NGC 3077

visible radio

Simulated collisions

animation

The redshifts of remote superclusters indicate that the

universe is expanding• During the 1920s, Edwin Hubble and Milton

Humanson were studying galaxy spectra• They found that galaxy spectral lines were

redshifted• They measured the distance to galaxies by

finding Cepheid variables and using the period-luminosity relationship

• They found that the most distant galaxies had the largest redshifts

• This is called the HUBBLE FLOW.

Hubble’s Law

slope = 75 km/s/Mpc called Hubble’s

Constant

Astronomers measure distances to distant galaxies using supernovae

and the Tully-Fisher relation• Standard candle method

• If you know how bright something really is and compare that to how bright it looks, then the distance can be determined

• Supernovae• All Type Ia supernovae have the same luminosity (M=-

19)• Tully-Fischer Relation

• The broader the spectral line, the faster it is rotating and the more luminous the galaxy.

Methods of estimating distance

• Parallax (up to 150 pc)• Spectroscopic Parallax (40pc-10kpc)• RR Lyrae variable stars (5-100 kpc)• Cepheid variables (1kpc-30Mpc)• Tully-Fisher relation (700kpc-150Mpc)• Type Ia supernovae (1 to 1000 Mpc)

Quasars look like stars but have huge redshifts• object with a spectrum

much like a dim star• highly red shifted• enormous recessional

velocity• huge distance (ala Hubble’s

Law)• must be enormously bright

to be visible at such a great distance

• Quasi-stellar object• QSO or Quasar

Active Galaxies bridge the energy gap between ordinary galaxies and

quasars• peculiar galaxies (pec)

• appear to be blowing themselves apart• Seyfert galaxies

• luminous, star-like nuclei with strong emission lines

• BL Lacertae objects (BL Lacs)• featureless spectrum with a brightness

that can vary by a factor of 15 times in a few months.

Radio image of Cygnus A showing a small but very bright radio galaxy in the

middle of the 320,000 ly wide lobes

Active galaxies lie at the center of double radio sources

Supermassive black holes lurk at the centers of some

galaxies• High resolution spectroscopy allows

astronomers to peak at the motion of gas near centers of galaxies

• Some galaxies exhibit high-velocity jets of material leaving the center

• Observations suggest that the centers of some galaxies are incredibly massive

• All of this suggests the existence of supermassive black holes

Galaxy (which is

actually quite large)

Intergalactic gas jet

Giant Gas Clouds

(surrounding the galaxy)

Jets of matter ejected from around a black hole may explain quasars and

active galaxies

Jets of matter ejected from around a black hole may explain quasars and

active galaxies

From where you observe it might make all the difference ...

TONIGHT:Telescope observations

• 8:45 pm Tuesday, May 20, after night class (telescopes on the roof)

• Weather permitting (looks good!)• Attendance not required, but

strongly recommended and will be for credit

• If you can’t make it, see me for an alternate assignment

Class Websitehttp://www.hartnell.edu/faculty/kjordahl

All lectures from the semester will be available by next week (as HTML and PowerPoint)

Catch up on your reading in the textbook!