1. Extreme Stars
Our Sun is more massive than about what percentage of stars?
How many orders of magnitude less metals does the record holder, HE , have than the Sun?
3. What is the temperature of the coolest white dwarf found so far?
In what constellation can you find Polaris?
The spectral type of Polaris A, B, and C all have the letter …
How far above the horizon is Polaris, as seen from Atlanta?

2. Extreme Stars
Our Sun is more massive than about what percentage of stars?
90%
How many orders of magnitude less metals does the record holder, HE , have than the Sun?
1/250,000 = 5 orders of magnitude
3. What is the temperature of the coolest white dwarf found so far?
4300 K, cooling for 8-9 Gyr
In what constellation can you find Polaris?
Ursa Minor
The spectral type of Polaris A, B, and C all have the letter … F
B. How far above the horizon is Polaris, as seen from Atlanta?
33.5 ± 1 degrees

3. Neutron Stars
Progenitor single: one massive (> 8 Msun) star with Fe core
double: one star + white dwarf … mass slurping
Process 1. p+ and e– crushed together into n and neutrinos
2. BOUNCE = SN EXPLOSION
3. shock wave blows star apart
4. neutron degeneracy pressure stabilizes core
shock wave not centered so some of central core survives bounce

4. Neutron Stars

5. Neutron Stars
Progenitor single: one massive (> 8 Msun) star with Fe core
double: one star + white dwarf … mass slurping
Process 1. p+ and e– crushed together into n and neutrinos
2. BOUNCE = SN EXPLOSION
3. shock wave blows star apart
4. neutron degeneracy pressure stabilizes core
Observe radio pulses … pulsar for millions of years
regularity … ROTATION
narrowness … SMALL OBJECT
Notes not really a “star”
1.4 Msun … 20 km in diameter
intense magnetic fields … not all neutron stars are pulsars
shock wave not centered so some of central core survives bounce

6. Neutron Stars
Chandra picture + Hubble picture

7. Millisecond Pulsar

8. Black Holes
Progenitor single: one massive (> 20 Msun) star with Fe core
double: one star + neutron star … mass slurping
Process 1. core more than 3 Msun
2. neutrons can’t hold against gravity!
3. matter “crushed” into no size
4. gravity so intense, not even light can escape …
Observe nothing (directly) … in binary systems
X-ray source … ENERGETIC
large star tossed … MASSIVE
gas flowing … BINARY
no object seen … DARK
variability … TINY
shock wave not centered so some of central core survives bounce

9. Cygnus X-1

10. Black Holes Notes black holes ARE NOT vacuum cleaners
black holes ARE heaters and eaters
Special nothing goes faster than light
Relativity

11. Special Relativity

12. Black Holes Notes black holes ARE NOT vacuum cleaners
black holes ARE heaters and eaters
Special nothing goes faster than light
Relativity
General light is affected by gravity

13. General Relativity
General Relativity

14. Light Affected by Gravity?!
photon signals from spacecraft may have tortured trajectories

15. Black Holes General light is affected by gravity Relativity
photons use energy to dig their way out of black hole
 redshift as we see them
 photon frequency as clock ticks … time dilation

16. Schwarzchild Radius PE = KE GMBHmph/R = (1/2)mphv2 R = 2GMBH/c2
imagine a photon at the “event horizon” --- same as the “Schwarzchild radius”
PE = KE
GMBHmph/R = (1/2)mphv2
of course, v = c
R = 2GMBH/c2
(this is the classical derivation, but the relativistic derivation yields the same result)
Sun ~ 3 km
Earth ~ 9 mm

17. Black Holes

18. Cluster Evolution
“banana peel”

19. Open Clusters Examples Pleiades and Hyades in Taurus
Characteristics 1. in Milky Way
2. loose aggregate
3. few hundred stars
4. young … less than 500 million yrs
5. massive stars still present
6. gas and dust
7. heavy metals

20. Hyades
use IC2391 ???

21. Globular Cluster M80

22. Globular Clusters Examples M13 in Hercules, Omega Centauri
Characteristics 1. outside of Milky Way
2. tight ball
3. few hundred THOUSAND stars
4. old … more than 10 billion yrs
5. G, K, M stars, red giants, white dwarfs present
6. no gas and dust
7. few metals

23. Globular Cluster: Mult Main Seq
Bedin et al. 2004
 Centauri with HST
observe:
double main sequence
multiple turnoffs
multiple subgiant branches
deduce:
different He content?
two star formation epochs?
star cluster/tidal tail behind?

24. …………………………………..

25. Calculate the densities in grams/cubic centimeter (g/cm3) of
Densities of the Stars
Calculate the densities in grams/cubic centimeter (g/cm3) of
A. our Sun today Msun Rsun
B. Sirius Msun Rsun
C. Proxima Centauri Msun Rsun
D. Betelgeuse (red supergiant) Msun Rsun
E. future Sun (white dwarf) Msun Rsun