Lecture 11:Galaxies and Their

Nuclei

The Hubble Deep Field

Eye on a Dime

The Hubble Ultradeep Field

Brief Review of Galaxy Structure

Disks Prominent feature in spiral galaxies (like Milky Way)

Stars in nearly circular orbits

Analogies: Solar System, accretion disk

BulgesCoexist with disks in spirals (central bulge, halo)

Elliptical galaxies: whole galaxy is bulge

Stars in random orbits

Galaxy Disks

Artist’s Impression ofOur Galaxy’s Disk

Disk of theGalaxy NGC 1672

Galaxy Bulges

Sombrero Galaxy – Notethe Large Bulge

Galaxy Classification

Main Contents of Galaxies

• Dark Matter (~80% of halo, smaller proportion of disk)

• Stars– Large galaxy has 100 billion stars (range 107-1012 stars)– “Collisionless”, interact by gravitational forces

• Gas – > 10% of star mass– “Dissipative”, tends to form clouds, sink to center– Can fall in from outside or escape in wind

• Dust– About 1% of gas mass, follows gas motion– Obscuration

The Milky Way in Optical Light

The Milky Way in Infrared Light

The Galactic Center in the Near Infrared

Relative Stellar Densities

Routes to a Supermassive Black Hole

Infrared Image of Galactic Center

The Radio Source Sgr A*

The Radio Source Sgr A*

The red dotat the centeris Sgr A*

Stellar Motions Near Sgr A*

Chandra X-ray Image of Galactic Center

Chandra X-ray Image of Sgr A*

X-ray Flare from Sgr A*