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Charles Hakes Fort Lewis College 1 Charles Hakes Fort Lewis College 2 Chapter 12 Stellar Evolution/ Supernovae Charles Hakes Fort Lewis College 3 Outline • Test 3 Wednesday • Death of Low-mass Stars • Death of High-mass Stars Charles Hakes Fort Lewis College 4 Current Events • http://apod.nasa.gov/apod/ap111109.html • http://www.youtube.com/watch?feature=pla yer_embedded&v=vtEvuz_oQ5o • http://www.space.com/scienceastronomy/g reen-brown-dwarf-star-spotted101110.html • http://news.discovery.com/space/top-5space-spirals.html Charles Hakes Fort Lewis College 5 Figure 12.10 White Dwarf on H–R Diagram 12 - For 1 solar mass stars, that is all that will fuse. • (need 600 million K for the next reactions to occur.) • The outer shell gets “blown off” by the hot, dense, core. • Result is a planetary nebula around a white dwarf (13). Charles Hakes Fort Lewis College 6 Figure 12.9 Planetary Nebulae Charles Hakes Fort Lewis College 7 Figure 12.12 Distant White Dwarfs - globular cluster M4 Charles Hakes Fort Lewis College 8 Figure 12.11 Sirius Binary System - nearby example of a white dwarf Charles Hakes Fort Lewis College 9 Figure 12.14 Close Binary System Charles Hakes Fort Lewis College 10 Figure 12.13ab Nova • • Charles Hakes Fort Lewis College 11 A nova forms when the temperature in the accretion disk reaches 107 K (H fusion). Such a star might “go nova” dozens (if not hundreds) of times. Figure 12.13c Nova Charles Hakes Fort Lewis College 12 Figure 12.15 Nova Matter Ejection Charles Hakes Fort Lewis College 13 High Mass Stars Charles Hakes Fort Lewis College 14 Figure 12.16 High-Mass Evolutionary Tracks • • Charles Hakes Fort Lewis College 15 Intermediate mass (~4 Msun) stars fuse carbon, but end up as white dwarfs. High mass (>10 Msun) stars evolve rapidly. Helium (and other) fusion begins before the star ever gets to the Red Supergiant stage. Figure 12.16 High-Mass Evolutionary Tracks Charles Hakes Fort Lewis College 16 • Wolf Rayet stars (are really big ones) have very strong winds. • http://upload.wikimedia.org/wi kipedia/commons/4/49/Crescen thunter.jpg When fusion is happening in the core of a star, the core is A) heating and shrinking B) heating and expanding C) cooling and expanding D) in equilibrium Charles Hakes Fort Lewis College 17 When fusion is happening in the core of a star, the core is A) heating and shrinking B) heating and expanding C) cooling and expanding D) in equilibrium Charles Hakes Fort Lewis College 18 When fusion stops in the core of a star, the core is A) heating and shrinking B) heating and expanding C) cooling and expanding D) in equilibrium Charles Hakes Fort Lewis College 19 When fusion stops in the core of a star, the core is A) heating and shrinking B) heating and expanding C) cooling and expanding D) in equilibrium Charles Hakes Fort Lewis College 20 Figure 12.17 Heavy Element Fusion • Each stage is faster than the stage before. • • • • • Charles Hakes Fort Lewis College 21 H - 10 million years He - 1 million years C - 1000 years O - 1 year Si - 1 week Figure 12.17 Heavy Element Fusion • Charles Hakes Fort Lewis College 22 Fusion of iron does not produce energy! Core-Collapse • The iron core shrinks and heats. • Photons are energetic enough to photodissociate iron nuclei. • Iron converted back to protons and neutrons. • This uses up energy - reduces pressure • Collapse accelerates! Charles Hakes Fort Lewis College 23 Core-Collapse • Protons and electrons combine to form neutrons releasing neutrinos. • Collapse continues until neutrons are in contact with each other. • Core “rebounds” and a shock wave throws off the outer layers of the star (mostly H and He.) Charles Hakes Fort Lewis College 24 Core-Collapse • Protons and electrons combine to form neutrons releasing neutrinos. • Collapse continues until neutrons are in contact with each other. • Core “rebounds” and a shock wave throws off the outer layers of the star (mostly H and He.) • This collapse takes about 1 second! Charles Hakes Fort Lewis College 25 Figure 12.18 Supernova 1987A Charles Hakes Fort Lewis College 26 Recent Supernovae Charles Hakes Fort Lewis College 27 Recent Supernovae Charles Hakes Fort Lewis College 28 Figure 12.19 Supernova Light Curves Charles Hakes Fort Lewis College 29 Figure 12.20 Two Types of Supernova Charles Hakes Fort Lewis College 30 Carbon Detonation (Type I) Supernova • Recall the accretion around a white dwarf star. • When the star reaches 1.4 Msun, the density and temperature allow carbon to finally fuse. • It fuses everywhere simultaneously. • Almost no hydrogen observed in the spectrum of Type I supernova. Charles Hakes Fort Lewis College 31 Figure 12.21 Supernova Remnants Charles Hakes Fort Lewis College 32 Formation of Heavy Elements • Elements heavier than iron require energy input for creation. • Supernovae provide the energy source. • The expanding cloud contains primarily H and He, but is enriched in heavy elements. • The Sun was created from “enriched” interstellar gas and dust. Charles Hakes Fort Lewis College 33 More Precisely 12-1 The Cycle of Stellar Evolution Charles Hakes Fort Lewis College 34 Three Minute Paper • Write 1-3 sentences. • What was the most important thing you learned today? • What questions do you still have about today’s topics? Charles Hakes Fort Lewis College 35