Astronomy 1020-H Stellar Astronomy Spring_2015 Day-36

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.

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.

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

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

 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.

 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!

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

 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.

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

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

 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.

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

 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.

 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.

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.

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.

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

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.

 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.

 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.