Galaxy Tutorial

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Slide 1

The Milky Way Galaxy

James Binney

Oxford University

Slide 2

Outline

Why it’s important

Components of the Galaxy

Nearby stars

Interstellar gas

The bar

The Galactic centre

Globular clusters

Star streams

The dark halo

Slide 3

Slide 4

Why bother?

It’s home!

It can be studied in unique detail

It’s a highly typical galaxy

Slide 5

Slide 6

Galaxy luminosity function

Few galaxies L>L*

Most light from galaxies with L~L*

No accident that L~L*?

Slide 7

Bulges and disks

We live at edge of disk

Disadvantage: structure obscured by “dust”

Advantage: can study motions of nearby stars

Slide 8

COBE Near IR View

Slide 9

Dimensions

Radius stellar disk 12 kpc=37000 light years

Distance Sun to centre 8kpc=24000 l.y.

Half-mass radius ~40kpc?

Thickness stellar disk ~400pc=1200 l.y.

Stellar mass ~5£1010 M¯

Gas mass ~5£109 M¯

Slide 10

The gas layer

At Sun surface density ~1020 atoms / cm2

Gas layer ~300 light years (3 1020cm) thick, so n~0.3 atoms / cm3

Density of air ~1020 atoms / cm3

So squashed to density air layer ~1 cm thick

Can see ~1kpc; when squashed could see only ~ 10cm through it

Yuk!

Slide 11

Star formation

Stars form at rate few / yr

Trifid nebula

Spitzer space telescope (IR)

Slide 12

Stars near the Sun

Stars born on nearly circular orbits

Stars have random velocities

Spiral structure increases random velocities over time

Derive age of solar neighbourhood: 12.2Gyr

Hipparcos data

Slide 13

Spiral structure

Local Standard of Rest (LSR) on circular orbit around GC

Shifts stars radially