1	Astro 1050 Wed. Oct. 30, 2002 Today: Review Exam Start Ch. 11: Neutron Stars & Black Holes
2	Exam #2 Results Results posted on WebCT Mean was a 58. Curve is 17 points. Too long (esp. with the table questions)? Solar evolution on HR diagram important See me if you have questions about the grading Will be included on prelim grades Lab is 25% and will help grades
3	The Crab Nebula – Supernova from 1050 AD Can see expansion between 1973 and 2001 Kitt Peak National Observatory Images
4	What happens to the collapsing core? Neutron star (more in next chapter) Quantum rules also resist neutron packing Densities much higher than white dwarfs allowed R ~ 5 km r ~ 10¹⁴ gm/cm³ (similar to nucleus) M limit uncertain, ~2 or ~3 M_Sun before it collapses Spins very fast (by conservation of angular momentum) Trapped spinning magnetic field makes it: Act like a “lighthouse” beaming out E-M radiation (radio, light) pulsars Accelerates nearby charged particles
5	Spinning pulsar powers the Crab nebula Red: Ha Blue: “Synchrotron” emission from high speed electrons trapped in magnetic field
6	Another pic of the Crab, Pulsar
7	Why a “pulsar?”
8	“Lighthouse” Model for Pulsars
9	Another Neutron Star in a SNR
10	Other cool stuff about Neutron Stars Novel Dragon’s Egg by Robert L. Forward Short Story “Neutron Star” by Larry Niven Binary Pulsars Gamma Ray Bursts? Pulsar Planets
11	Black Holes -- basics Nothing we know of can stop collapse after neutron pressure fails Consider escape velocity from the surface at radius R: As R shrinks (but M is fixed), V_escape gets larger and larger At some point V_Escape= c (speed of light) Happens at Schwarzschild radius Not even light can escape from within this radius
12	Examples: The Schwarzschild Radius: Mass in solar masses R_s (km) 10 3 2 1 0.000003 (Earth)
13	Examples: The Schwarzschild Radius: Mass in solar masses R_s (km) 10 30 3 9 2 6 1 3 0.000003 (Earth) 0.9 cm
14	Black Holes -- details Remember – gravity is same as before, away from mass Black holes do NOT necessarily pull all nearby material in A planet orbiting a new black hole would just keep on orbiting as before (assuming the ejected material or radiated energy didn’t have an effect) Any mass can potentially be made into a black hole – if you can compress it to a size smaller than R_S = 2GM/c² 1 M_Sun: 3.0 km 10⁶ M_Sun 3´10⁶ km 1 M_Earth 8.9 mm If you do make material fall into a black hole, material will be falling at close to the speed of light when it reaches R_S If that falling gas collides with and heats other gas before it reaches R_S, then light from that hot material (outside R_S) can escape.
15	Black Holes – detection By definition – can’t see light from black hole itself Can see large amounts of energy released by falling material just before it crosses R_S Can see motion of nearby objects caused by gravity of black hole Example: Like White Dwarf accretion disk but w/ black hole instead Gas from red giant companion spills over towards black hole Gas spirals in toward black hole, through accretion disk Gas will be much hotter because it falls further, to very small R_S Gas will be moving at very high velocity Much faster than with white dwarf since much closer (P² µ a³) Signature of black hole: Very high energy release, very high velocity We will find MASSIVE black holes in centers of most galaxies
16	Cygnus X-1
17	More Cool Stuff About Black Holes Time Dilation – originally “Frozen Stars” Gravitational Redshift Wicked Tidal Forces Hawking Radiation