The Size and Structure of the Milky Way Galaxy

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The New View of the Milky Way

Dadark matter halo

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Dark Matter: A Major Problem for Contemporary Physics and Astronomy

Stars are a small fraction of the mass of major galaxies

The dark matter problem becomes more pronounced as you go out in the universe

The form of the dark matter is unknown; probably not what you studied in chemistry

Possibly/probably an unknown form of elementary particle

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At the Very Center

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What do we see at the galactic center (radio and infrared wavelengths?

Strong radio source (synchrotron radiation)

At infrared wavelengths, can see stars orbiting very vast around Sgr A

Ten years of observations speeded up

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The Orbit of Star S2

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Star S2 passes about as close to Sagittarius A* as the planet Pluto passes to the Sun. Indicates supermassive object in a very small region

Andrea Ghez paper