1. Astronomy 1020-H Stellar Astronomy Spring_2015 Day-36

3. Course Announcements Dark night Alternative exercise is posted. Reports are due TODAY Solar Rotation Project due Mon. Apr. 27 Final Exam (and Exam-4) is (are) scheduled for Thursday, May 7, 1:30-3:30pm. IF there is consensus, this could be moved to a different (more convenient) time.

4. Star Formation & Lifetimes Lecture Tutorial pg. 119 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on and write complete thoughts into your LT. If you get stuck or are not sure of your answer, ask another group.

5.  Core collapses, central temperature rises.  Photodisintegration, neutrino cooling reduces pressure, collapse accelerates.  Electron degeneracy cannot help.

6.  Collapses until it reaches nuclear densities.  At these high densities, nuclear forces repel atoms.  Core stops, bounces back, driving a shock wave through star.

7.  Shock wave takes a mere few hours to rip through the star.  Outer layers blow off in tremendous explosion (Type II supernova).  Dense core remains.

8.  Light energy emitted is about 1 billion Suns.  Kinetic energy of blown-off outer parts: 100x.  This kinetic energy is transferred to the interstellar medium (ISM), heating it.  Neutrinos carry off an energy of 100 times larger still!

9.  Shock wave heats and pushes the ISM.  New elements created in the explosion (nucleosynthesis).  Most atoms heavier than iron are made in supernova explosions.

11.  If the star is not too massive, the Type II supernova leaves behind a neutron- degenerate core: neutron star.  Mass between 1.4 and 3 M , radius ~ 10 km.  Some neutron stars are found in X-ray binaries, and give off strong X-rays.

12.  Neutron stars are incredibly dense and therefore have very high surface gravity and escape velocities.  Surface gravity:  Escape velocity: MATH TOOLS 17.2

13.  Others are found as pulsars (rapidly rotating neutron stars).  Highly magnetized.  Beam of radiation sweeps by Earth like a lighthouse beam.

14.  The Crab Nebula is the remnant of a Type II supernova first witnessed by the Chinese in 1054 CE and recorded as a “guest star,” lasting in the sky for over three weeks.  Its glow is powered by a pulsar.

16. Concept Quiz—Supernova What type of star makes a Type II supernova? A.a neutron star in a mass-transfer binary B.a black hole C.a pulsar D.a single massive star

17.  Star clusters are bound groups of stars, all made at the same time from the same material.  Globular clusters are very dense with up to millions of stars.  Open clusters are looser, with a few dozen to a few thousand stars.

18.  H-R diagrams of open and globular clusters look very different due to stellar evolution since the stars in them all formed around the same time: snapshots of evolution.

19. Star Clusters and Stellar Evolution  Young clusters still have massive stars on MS.  In older clusters, massive stars have died.  Location of main-sequence turnoff gives cluster age.

20. Star Clusters and Stellar Evolution  Star clusters have different colors relating to the abundances of stars in them.  Reflects the idea of stellar populations: groups of stars with similar ages and other shared characteristics.  Young stars have more massive elements in them than older stars, and their clusters are bluer.  Supernovae seed the universe with massive elements.  Earth could not have the elements it has were it not for prior supernovae.

21. Concept Quiz—Ages Here is a table of the temperatures of stars at the main- sequence turnoff in four clusters. Which cluster is the oldest? ClusterNameTemp (K) AOrion22,000 BNGC 188 9,000 C47 Tuc 5,000 DM 67 7,000

22. Stellar Evolution Lecture Tutorial pg. 133 Work with a partner! Read the instructions and questions carefully. Discuss the concepts and your answers with one another. Take time to understand it now!!!! Come to a consensus answer you both agree on and write complete thoughts into your LT. If you get stuck or are not sure of your answer, ask another group.

24.  If the mass of a neutron star exceeds 3 M , it will collapse into a black hole.  Not even light can escape the gravitational pull of a black hole.  Can form directly from Type II supernova (if massive enough) or from accretion by a neutron star in a binary system.  Makes us question our assumptions about the nature of space and time.

25.  An event describes something that happens at a specific location and specific time.  Special relativity describes the relationship between events in space and time.  Combines those two aspects into a four- dimensional spacetime.  Something that must be analyzed using special relativity is called relativistic.  Newton’s laws don’t apply to the universe, but they are not wrong; they are contained in special relativity.