Chapter 25:Our Galaxy

Physics of Astronomy – week 6 – May 2006

RR Lyrae variables

Q: Why are they all about 100 Lsun?

A: Horizontal branch pulsators:

heating and compressing at roughly

constant luminosity (T↑ and R↓)

The winding dilemma – if star motion caused spiral arms, structures would disappear in just a few hundred million years

Galactic density wave causes traffic jams in interstellar medium

Black hole at the center of MW

Orbits of nearby stars show that SagA* has about 3.7 million Msun – very massive

X-ray flares detected by Chandra last only 10 minutes, indicating a size of only 1.2 AU – very compact

Looking ahead• Monday: no HW due, no presentations

• Tuesday: Bring your finished PowerPoint pages

• 3:00 workshop Tues: PowerPoint → Posters

• Thursday: bring everything to class - we’ll walk to the van together and leave at 3:00

• Summary: Maxwell’s equations → speed of light “greatest synthesis …more important than the civil war”