“Politics is the art of looking for trouble, finding it everywhere, diagnosing it incorrectly, and applying the wrong remedies.” Groucho Marx Test 2 on Friday

What supplies the energy to support a main sequence star? Q&A Time! What supplies the energy to support a main sequence star?

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.

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?

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)

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. 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.

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?

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.

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

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

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?

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.

Q&A Time! The last solar minimum (minimum sun spots) occurred in 2008. When can we expect the next one?

Q&A Time! The last solar minimum (minimum sun spots) occurred in 2008. When can we expect the next one? The sunspot cycle is 11 years, so the next minimum will be in 2019. (22 years for a complete solar cycle to get the magnetic field back the same way.)

How do we determine masses for stars? Q&A Time! How do we determine masses for stars?

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.

Q&A Time! Sirius is a white star and Betelguese is a red star. Which star is hotter?

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. 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.

What provides the support for a neutron star? Q&A Time! What provides the support for a neutron star?

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

Q&A Time! Which is larger in radius, a 0.4 solar mass white dwarf or a 0.8 solar mass white dwarf?

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.

What created the iron in your chairs? Q&A Time! What created the iron in your chairs?

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.

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

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

Wormholes

The Graviton: A gravity analogy to the photon

Wormhole Ingredients Be able to control gravitons Make anti-gravitons Bend space using (anti-)gravitons. Connect both pieces of space using (anti- )gravitons Hold hole open using anti-gravitons

How to build a time machine.

Time machine ingredients 1) Build 2 black holes. 2) Connect the black holes with a wormhole. 3) Move one of the black holes near the speed of light for a very long time (let's say 0.9c for 200 years) 4) Travel through the still wormhole to the moving one. (You've gone back 113 years!)

A thought experiment Imagine what we could do if we could control the graviton (gravitational fields) the same way we can control the photon, or the electron (electric fields).

Back to

Stellar Populations Right now, our Sun has about 2% 'metals'. When it dies, the nebula will have 3-4% 'metals'. The star before our Sun was created with ~1% 'metals'. What if we keep going backwards?

Stellar Populations As stars recycle heavier material back into space, newly formed stars incorporate this material. Thus newer stars have more “metals” then old stars. This gives us populations: I: Stars like our Sun- they have the most metals (2%) II: Metal-poor stars- formed in the galaxy before our Sun: have some, but little metals (<0.1%) III: No metals at all: made only of H and He. The first stars.

Stars form in groups or clusters

They contain O and B type (Pop I) stars (plus all other types too). OB Associations are 10-100s of stars, not gravitationally bound that formed at the same time (within a few million years). They contain O and B type (Pop I) stars (plus all other types too).

Open clusters are also a group of unbound stars, but without O and B stars. They can appear richer as stars have had more time to form. They have Pop I stars.

They have Population II stars Globular clusters contain up to millions of stars. They are gravitationally bound together and are very old, with only low mass stars remaining. They have Population II stars

A nearby supernova caused our pre-solar cloud to collapse. Our Sun was most likely formed within an open cluster that has since dissipated. A nearby supernova caused our pre-solar cloud to collapse.

Take aways Stars form in groups. Most groups are not gravitationally bound, but the rich ones (globular clusters) are.

Stars within 10pc (32.4ly)