The Milky Way (Spiral Galaxies)

Spiral Galaxies

• Thin Disk (~30 kpc in diameter and ~1 kpc thick) of stars, gas, and dust: open clusters, young stars. Sun is located 8 kpc away from the Galactic Center

• Thick Halo of stars with little gas or dust: globular clusters, old stars

• The Bulge (~1 kpc) is the center of the galaxy where the inner halo & the disk merge together: a supermassive (>106 solar mass) black hole in the center.

Edge-on view

Face-on view

3D view of the Milky Way

The Problem of Absorption

• Interstellar space is filled with gas and dust • This dust absorbs and scatters starlight passing

through it, • This makes more distant objects look fainter

than they otherwise would be if there were no interstellar dust.

• Blocks out light from distant stars.