Finding the Milky Way in the Galaxy

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Slide 69

The Galactic Center

Center of the Milky Way

Stars orbiting the black hole

X-ray flares from the black hole

Slide 70

Fish eye MW

Slide 71

Radio image, central 3 ly

Center is the red ellipse at the center

Called Sgr A*

Slide 72

Infrared image, central 3 ly

Sgr A* does not appear.

There are about 1,000,000 stars in the area covered by this image.

Stars are only 1000 AU apart.

Slide 73

Stellar Orbits in the Galactic Center

Slide 74

Mass of Sgr A* can be measured using stellar orbits

Fastest moving star moves at 2% of the speed of light, 5000 km/s

Mass is about 3 million solar masses

Emits radio and X-rays

Almost certainly a black hole

Slide 75

X-ray image, central 3 ly

Sgr A* is the bright object in the center of the image.

Makes flares in X-rays.

Movie.

Slide 76

Observations of nearby star orbits in IR

Radio observations of accretion disk

Orbit of stars in spiral arms [Kepler’s 3rd law]

X-ray observations of coronal gas

Dark matter studies using rotation curves

The best estimate of the mass of the black hole at the galactic center was made using:

Slide 77

Review Questions

What properties of a star’s orbit around the Galaxy enable one to measure the mass inside its orbit?

What is the shape of the rotation curve of the Milky Way and why is was it unexpected?

What lies at the center of the Milky Way?