The Size and Structure of the Milky Way Galaxy

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The Size and Structure of the Milky Way Galaxy

We live in a new class of astronomical object

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First… an advertisement for 29:52 “Exploration of the Solar System”

The other half of astronomy

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Observations indicate the shape and size of the Milky Way Galaxy

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Structure of the Milky Way

Disk

Bulge

Galactic center

Galactic halo

Question: what simple observation

Is consistent with a part of this picture?

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A view of the Milky Way with an artist’s touch

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Next topic: the motion of the Sun in the Milky Way (leads to something extremely interesting)

How does the Sun move in the Milky Way?

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Next topic: the motion of the Sun in the Milky Way (leads to something extremely interesting)

How does the Sun move in the Milky Way?

V=220 km/sec

The sun moves in response to the gravitational force of

All the rest of the mass in the galaxy

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How is the mass distributed?

How could we tell?

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Force of Gravity acts on the Sun and all objects in the Galaxy

Gravity has magnitude and direction

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Sun responds to net force by moving on circular path around the galactic center

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Mass distributions like 1,2, and 3 give circular orbits with V(R)

A plot of V versus R is called a rotation curve

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The Observed Case for the Milky Way

No sign of the “root-R falloff”

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Significance of the Rotation Curve for the Milky Way

Rotation curve stays high outside the bulk of the stars

Mass indicated by the rotation curve exceeds that in stars

Most of the mass of the Milky Way is in an unknown form of “Dark Matter”

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