Announcements Homework #10: due today Solutions and study guides will be posted online. Final Exam scheduled for May 22nd @ 12:15. Bring a scantron form 882-EZ Need extra help? Come to SCI 242 on Thursday, 5/17, at either 10AM or 3PM.
Stellar Remnants: White Dwarfs, Neutron Stars, & Black Holes (Chp. 14)
Black Holes: • Progenitor mass: > 10-20 MSun • Schwarzscild Radius • Event Horizon • What is the event horizon for a 1 MSun object? • Observational Evidence for the existence of BH’s • X-Ray Binaries • Center of the Milky Way
Eclipsing X-Ray Binaries Accretion disk emits x-ray radiation
Mass of central object: 3 Million MSun!! Orbit of S2: P=15.2 years; a=900 AU Mass according to Kepler’s laws: 3.5x106 MSun! Luminosity: below detection threshold Closest approach: 17 light-hours
The Milky Way Galaxy (Chp. 15)
Looking up at the sky at night, we can see that the Sun is one of (at least) thousands of stars. We also see that the stars in the sky are not uniformly spread out.
Milky Way NGC 891
Angle between Solar System plane and Galactic plane 62 degrees
Disk • Distribution of stars, gas, and dust with a diameter of about 30 kpc (100,000 light-years) and plane tilted with respect to Earth’s orbit around Sun • Rotation with all objects circling in the same direction • High density of stars near center (10 million stars per cubic light-year) to low density farther out (0.003 stars per cubic light-year at Sun)
Halo • Roughly spherical region (disk embedded) • Contains mainly old stars, such as globular clusters • Bulge • Flattened collection of stars surrounding dense core of galaxy • About 1/3 the diameter of the galaxy
Milky Way: • Herschel’s star counts • Shapley’s work with globular clusters • size (50,000 pc across; 100-1000 pc thick) • location of Sun (8,000 pc from center) • Components: bulge, disk, halo • Motion • bulge versus disk • direction of Sun’s motion with respect to spiral arms • Angle between ecliptic and Milky Way • Spiral Structure • “traffic jam” • young stars found in spiral arms