More than just a candy bar. The Milky Way More than just a candy bar.

Goals Structure of our Galaxy. Its size and shape. How do stars and things move through it? The Galactic Center. How does the Milky Way compare to other galaxies?

The Milky Way Stars Dust Gaseous Nebulae Open Clusters Globular Clusters Pulsars Black Holes How do they all fit together to make our galaxy?

Optical emission from stars and nebulae

Near-Infrared emission from stars – copyright E. L. Wright and COBE

Far-Infrared dust emission – copyright E. L. Wright and COBE

Radio emission from neutral hydrogen – copyright J. Dickey

Near-Infrared stellar emission – copyright E. L. Wright and COBE

John P. Gleason M51 - Copyright HST

Where are We? Not at the center of the Milky Way. Where is the center? Globular Clusters point the way. M10 – copyright Credner and Kohle

You Are Here

Concept Test If the Earth were located at the center of the galaxy, we would see: Globular clusters in only one direction. Globular clusters in all directions. Many more supernovae than we do now. Many more stars being formed than we do now. None of the above.

30 kpc 8.0 kpc 1 kpc

The Sun’s “age” We define our age by trips around the Sun. How many trips of Sun around Milky Way? R = 8.5 kpc V = 220km/s P = 2.5x108 yrs 20 trips. R V

The Heart of the Galaxy Because of all the dust in the Galaxy, we can’t see its center in visible light. Can use IR and radio to pierce the dust.

200 pc 5 pc Sagittarius A* - Sgr A*

Supermassive Black Hole Infrared images of stars in the Galactic Center over 8 years. The “+” is the radio source Sgr A* Conclusion: Must be over one million solar masses within less than 1/5 of a light year! Event Horizon ~ 0.02 AU! D = 7.94 +/- 0.42 kpc. Copyright Eckart & Genzel

Copyright – FORS1 VLTI, European Southern Observatory

Hubble Tuning Fork

Ellipticals

Ellipticals Huge No gas. No dust. No young stars. Nothing but old stars. Random orbits.

M 87 Copyright – Anglo-Australian Telescope Board Copyright - HST

Hubble Tuning Fork

Copyright – Adam Block, KPNO

Spirals

Spirals Like Milky Way. Disks and bulge. Young stars and old. Gas and dust. Stars forming. Stars dying. M81 and M82 – Copyright R. Gendler

M63 Copyright – S. Miyazaki, Suburu

NGC1365 Copyright – VLT

M33 – Copyright NOAO

John P. Gleason M51 - Copyright HST

NGC 4314

NGC 891 – Copyright WIYN NGC 891 – Copyright J.C. Barentine, NOAO

Sombrero Galaxy – Copyright P. Barthel VLT M10 – copyright Credner and Kohle Sombrero Galaxy – Copyright P. Barthel VLT

NGC 4526

Irregulars

Homework #16 For Wednesday: Read: Bennett Ch12 Do Quiz 12