1. On-line grades updated to include GP1.
“Physics is like sex: sure, it may give some practical results, but that’s not why we do it.”
Richard Feynman
Test 2 on Friday
On-line grades updated to include GP1.

2. MASS HR Diagram The difference between this star and this star is Blue
Red

3. Evolutionary Stage HR Diagram The difference between this star and
this star is
Evolutionary Stage
Blue
Red

4. Evolution of stars with >8 solar masses.
(2% of all stars)
Gravity
Fusion H to He
M< M>8
Fusion Other (He,C,...Si)
Gravity: Implosion
M<25<M
Neutron degeneracy pressure.
Gravity: Nothing

5. Eventually, all black holes evaporate.
Hawking Radiation:
Eventually, all black holes evaporate.

6. This will be an in-class assignment worth 15 points.
Q&A Time!
This will be an in-class assignment worth 15 points.
Group up into groups of 3-4.
One piece of paper for the group.

7. Q&A Time! 1) What supplies the energy to support a main sequence star?
2) What is the size (event horizon) of a 30 solar mass black hole?
3) What causes a horizontal branch star to stop being a horizontal branch star?
4) Which is brighter, a 2 solar mass main sequence star or a 3 solar mass main sequence star?
5) By how much is it brighter?

8. Q&A Time! What stage of evolution is the each arrow pointing to?6 8 7 9

9. 12) How do we determine masses for stars?
10) Two stars in a cluster appear to be equally bright. Star A is yellow and Star B is red. What else do I know?
11) The last solar minimum (minimum sun spots) occurred in When can we expect the next one?
12) How do we determine masses for stars?
13) Sirius is a white star and Betelguese is a red star. Which star is hotter?

10. 14) What provides the support for a neutron star?
Q&A Time!
14) What provides the support for a neutron star?
15) Which is larger in radius, a 0.4 solar mass white dwarf or a 0.8 solar mass white dwarf?
16) What created the iron in your chairs?

11. 17) What is the difference between these 2 stars?
HR Diagram
17) What is the difference between these 2 stars?
Blue
Red

12. We will use your clickers
Answer Time!
We will use your clickers

13. 1) What supplies the energy to support a main sequence star?
Answer Time!
1) What supplies the energy to support a main sequence star?
A) Fusion of H → He
B) Fusion of He → C
C) Gravity
D) Nothing.

14. 2) What is the size (event horizon) of a 30 solar mass black hole?
Answer Time!
2) What is the size (event horizon) of a 30 solar mass black hole?
A) 30 km.
B) 90 km.
C) 900 km.
D) infinitely small.

15. B) It runs out of H in the core. C) It runs out of He in the core.
Answer Time!
3) What causes a horizontal branch star to stop being a horizontal branch star?
A) It collapses.
B) It runs out of H in the core.
C) It runs out of He in the core.
D) It explodes.

16. C) They are the same brightness D) There is no way to tell.
Answer Time!
4) Which is brighter, a 2 solar mass main sequence star or a 3 solar mass main sequence star?
A) 2
B) 3
C) They are the same brightness
D) There is no way to tell.

17. 5) By how much is it brighter?
Answer Time!
Which is brighter, a 2 solar mass main sequence star or a 3 solar mass main sequence star?
5) By how much is it brighter?
A) 2 times brighter
B) 4 times brighter
C) 8 times brighter
D) 16 times brighter

18. Q&A Time! What stage of evolution is the each arrow pointing to?
A) Main sequence
B) Red giant
C) Horizontal Branch
D) AGB
E) Planetary Nebula
F) White Dwarf 6 8 7 9

19. 10) Two stars in a cluster appear to be equally bright
10) Two stars in a cluster appear to be equally bright. Star A is yellow and Star B is red. What else do I know?
A) A is larger
B) B is larger
C) A is closer
D) B is closer

20. 11) The last solar minimum (minimum sun spots) occurred in 2008
11) The last solar minimum (minimum sun spots) occurred in When can we expect the next one?
A) It happened in 2009
B) It happened in 2015
C) 2019
D) 2030

21. 12) How do we determine masses for stars? A) With a scale
B) Using where it is on the HR diagram.
C) From stars in binaries.
D) There is no way to tell.

22. 13) Sirius is a white star and Betelguese is a red star
13) Sirius is a white star and Betelguese is a red star. Which star is hotter?
A) Sirius
B) Betelguese
C) They are the same.

23. 14) What provides the support for a neutron star? A) Fusion H → He
Q&A Time!
14) What provides the support for a neutron star?
A) Fusion H → He
B) Fusion He → C
C) Gravity
D) Electron degeneracy pressure
E) Neutron degeneracy pressure

24. D) there is no way to tell.
Q&A Time!
15) Which is larger in radius, a 0.4 solar mass white dwarf or a 0.8 solar mass white dwarf?
A) 0.4 solar mass WD
B) 0.8 solar mass WD
C) They are the same
D) there is no way to tell.

25. 16) What created the iron in your chairs?
Q&A Time!
16) What created the iron in your chairs?
A) Planetary nebula
B) supernova
C) Both A & B
D) Protostars.

26. 17) What is the difference between those 2 stars?
Q&A Time!
17) What is the difference between those 2 stars?
A) Age
B) Mass
C) Composition
D) Nothing.

27. Make sure everyone’s name is on the paper and turn it in.

28. What supplies the energy to support a main sequence star?
Q&A Time!
What supplies the energy to support a main sequence star?
Fusion of H to He.

29. What is the size of a 30 solar mass black hole?
Q&A Time!
What is the size of a 30 solar mass black hole?
Tricky, tricky! The size of the black hole is a point! The size of the Schwarzchild radius (event horizon) is 3*M in km: 3*30=90km
(about 60 miles in radius)

30. The core runs out of He sufficiently hot to do fusion.
Q&A Time!
What causes a horizontal branch star to stop being a horizontal branch star?
The core runs out of He sufficiently hot to do fusion.

31. The 3 solar mass star is brighter.
Q&A Time!
Which is brighter, a 2 solar mass main sequence star or a 3 solar mass main sequence star? By how much is it brighter?
The 3 solar mass star is brighter.
L=M3.5: LM=2=11.3Lsun, LM=3=46.8Lsun
L3/L2 = 46.8/11.3 = 4.1 times brighter.

32. Q&A Time! What stage of evolution is the ___ arrow pointing to?
Horizontal branch
Red giant branch
White dwarfs
Main sequence

33. Q&A Time!
Two stars in a cluster appear to be equally bright. Star A is yellow and Star B is red. What else do I know?
In a cluster, distance is the same. Since they are equally bright and A is hotter, B must be larger.

34. Q&A Time!
The last solar minimum (minimum sun spots) occurred in When can we expect the next one?
The sunspot cycle is 11 years, so the next minimum will be in (22 years for a complete solar cycle to get the magnetic field back the same way.)

35. How do we determine masses for stars?
Q&A Time!
How do we determine masses for stars?
Only for stars in binaries, where we can determine their gravity.

36. Q&A Time!
Sirius is a white star and Betelguese is a red star. Which star is hotter?
Sirius is hotter.
Betelguese is only slightly fainter, even though it's farther away. How come?

37. Betelguese is a supergiant, Sirius is a main sequence star.
Q&A Time!
Sirius is a white star and Betelguese is a red star. Which star is hotter?
Sirius is hotter.
Betelguese is only slightly fainter, even though it's farther away. How come?
Betelguese is a supergiant, Sirius is a main sequence star.

38. What provides the support for a neutron star?
Q&A Time!
What provides the support for a neutron star?
Neutron degeneracy pressure

39. Q&A Time!
Which is larger in radius, a 0.4 solar mass white dwarf or a 0.8 solar mass white dwarf?
The 0.4 solar mass white dwarf. More massive white dwarfs (and neutron stars) are smaller.

40. What created the iron in your chairs?
Q&A Time!
What created the iron in your chairs?
Either a planetary nebula or a supernova. Both are capable.

41. 17) What is the difference between those 2 stars?
Q&A Time!
17) What is the difference between those 2 stars?
B) Mass
It is the main sequence