Dark Stuff

1
Dark Stuff an interlude

• Toby Burnett

2
How do we measure mass?

• Weigh?
• Count the number of atoms?
• Gravitational effect?

3
Can we weigh this?
4
Measuring mass of distant galaxies

• If know v and R, then useFma mv2/R
  GmM/R2
• to get Mv2R/G
• M is enclosed mass
• How do we measure R, v?

v
M
R
5
A typical rotation curve
DarkMatter!!
6
The enclosed mass around Sag A
7
Stirring up the stars

• If one looks at this region with big telescopes
  and near-infrared cameras one can see lots of
  stars. If one takes pictures every year it seems
  that some stars are moving very fast (up to 1500
  kilometers per second). The fastest stars are in
  the very center - the position marked by the
  radio nucleus Sagittarius A (cross).