View
214
Download
0
Tags:
Embed Size (px)
Citation preview
Via Lactia
The band forms a complete ring We seem to be in the center of a disk of
stars
Clouds of gas and dust block our view so it
is hard to see beyond our local region
Discovering The Galaxy In the early part of the century Harlow Shapley
found the distance to globular clusters using Cepheid variables
Globular clusters
Unlike stars in the disk, we can see distant globulars Cepheid variables
If we can find luminosity and flux we can get distance (F = L/4d2)
The Center
Shapley found the distance to the globulars and plotted their positions
He found:
We are not at the center of the galaxy
and the disk extends out much further than we can easily see
How Do We Learn About The Milky Way?
Optical observations
Radio observations
Infrared observations
Observing other galaxies Since we are in the middle of the Milky Way
we can’t get an overview of it
Structure of the Milky Way
Disk
Nucleus
Halo Spherical distribution of old stars and
globular clusters around disk and bulge
The Disk The disk is very thin
Younger stars and star forming regions near the center, older stars above and below
Disk exhibits differential rotation (inner parts rotating faster than outer)
Spiral Structure We know that other galaxies have spiral
structure, but it is harder to see the Milky Way’s
We find spiral arms by tracing:
They are not uniformly distributed but
are found in a loose spiral structure How do spiral arms form?
Density Waves Spiral arms are like traffic jams
This can trigger star formation in the arms
The clouds eventually move out the other side
The spiral arm material changes, only the pattern stays the same
At the Core
The nucleus is the hardest part of the galaxy to observe due to all the gas and dust
One, Sagittarius A* (Sgr A*), may be the center of the galactic core What is it?
Properties of the Core
Stars near the core are very close together and moving very fast
Sgr A* is emitting enormous amounts of energy
A black hole
Massive Black Holes Sgr A* does not move and may have
jets and and accretion disk
Mass of ~1 million solar masses?
Our own is very hard to observe
The Halo The halo are stars orbiting in a large
sphere around the galaxy The halo is composed of old stars
Halo stars -- Population II -- metal poor Disk stars -- Population I -- metal rich
Halo stars formed formed early from relatively unprocessed material
Globular Clusters
Size: Shape: Contents:
Globulars are in elliptical orbits around the galactic center
Unlike open clusters in the disk, globular clusters are very tightly gravitationally bound
History of the Milky Way How did the galaxy form?
Basic theory has Milky way forming from large
spinning cloud of gas Halo formed first, and so is older and more metal
poor Disk is denser and so keeps forming stars and
building up metals