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Unformatted text preview: September 1, 2010 Reading assignment, Cosmic Catastrophes, Chapter 6 plus Section 5.1, Section 1.2.4 and Section 2.3 for background Last lecture posted as pdf on class web site Astronomy in the News? House threatens to cut funds for NASA science. 14 Nobel Prize winners, some astronauts, former NASA ofﬁcials, 30 total, signed a letter in favor of President Obama’s proposed space program, altering plans of previous administration. Pic of the Day – Earth and Moon from perspective of Messenger satellite orbiting Mercury Electronic version of Cosmic Catastrophes No limit to access through UT library by means of UT eid and password (go to UT library online, search for Cosmic Catastrophes, click on “electronic resource”) Downloads and printing are limited to 20% of the content. Quantum Pressure -- just depends on squeezing particles, electrons for white dwarf, to very high density -- depends on density only -- does not depend on temperature Important Implication: Normal Radiate energy, pressure tries to drop, star contracts and gets hotter (and higher pressure) White Dwarf Radiate energy, temperature does not matter, pressure, size, remain constant, star gets cooler Opposite behavior Normal Star Regulated White Dwarf Unregulated put in energy, star expands, cools put in energy, hotter, more nuclear burning -- explosion! Figure 1.3 A normal star can and will radiate away thermal energy and hence structural energy. A brick cannot radiate its structural energy, A white dwarf cannot radiate away its quantum energy. A normal star supported by thermal pressure regulates its temperature. If excess energy is lost, the star contracts and heats. If excess energy is gained, the star expands and cools. Feedback loop, akin to the furnace, thermostat in your house. A white dwarf, supported by the quantum pressure, cannot regulate its temperature. If excess energy is lost (the case for the vast majority of white dwarfs), they just get cooler. If Excess energy is gained, they heat up and can explode. Behavior of white dwarf, Quantum Pressure, worked out by S. Chandrasekhar in the 1930’s Limit to mass the Quantum Pressure of electrons can support Chandrasekhar limit ~ 1.4 M density ~ billion grams/cc ~ 1000 tons/cubic centimeter Maximum mass of white dwarf. If more mass is added, the white dwarf must collapse or explode! One Minute Exam If nuclear reactions start burning in an ordinary star like the Sun, what happens to the temperature? The temperature goes up The temperature remains constant The temperature goes down Insufﬁcient information to answer the question One Minute Exam If nuclear reactions start burning in a white dwarf, what happens to the temperature? The temperature goes up The temperature remains constant The temperature goes down Insufﬁcient information to answer the question SUPERNOVAE
Catastrophic explosions that end the lives of stars, Provide the heavy elements on which planets and life as we know it depends, Energize the interstellar gas to form new stars, Produce exotic compact objects, neutron stars and black holes, Provide yardsticks to measure the history and fate of the Universe. Reading: Chapter 6 Supernovae Also § 2.1, 2.2, 2.4 & 2.5 for background
Issues to look for in background: Why is it necessary for a thermonuclear fuel to get hot to burn - charge repulsion § 2.1 & 2.2 Core Collapse § 2.4 & 2.5 One type of supernova is powered by the collapse of the core of a massive star to produce a neutron star, or perhaps a black hole The mechanism of the explosion is still a mystery. The other type of supernovae (Type Ia) is thought to come from a white dwarf that grows to an explosive condition in a binary system. Chandra X-ray Observatory image Of Tycho’s supernova of 1572 These explode completely, like a stick of dynamite, and leave no compact object (neutron star or black hole) behind. Chapter 6 Supernovae
Historical Supernovae - in our Milky Way Galaxy observed with naked eye over 2000 years especially by Chinese (preserved records), but also Japanese, Koreans, Arabs, Native Americans, ﬁnally Europeans. SN 386 SN 1006 SN 1054 SN 1181 SN 1572 SN 1604 ~1680 SN 1987A Vela earliest record brightest Crab Nebula (Radio Source 3C58) Tycho Kepler Cas A nearby galaxy 10,000 years ago NS, jet? No NS NS, jets NS, jets No NS No NS NS? jets NS? jets NS, jets G11.2-0.3 = SN 386 65 ms pulsar axis structure X-ray image G11.2-0.3 = SN 386 X-ray image 65 ms pulsar Chandra axis structure Observatory X-ray image SN 1006 No evidence for neutron star SN 1181 = 3C58 66 ms pulsar axis/torus structure? X-ray image Crab Nebula
Remnant of “Chinese” Guest Star of 1054
Optical Image Chandra Observatory X-Ray Image Left-over jet Crab 33 ms pulsar axis/torus structure Kepler Tycho Chandra Observatory X-ray Image of Tycho’s Supernova of 1572 No evidence for neutron star SN 1006 Great Observatories composite of Kepler’s supernova 1604 No sign of neutron star “sideways” alignment? SN 1572 Tycho Cassiopeia A by Chandra X-ray Observatory
Jet Counter Jet Compact remnant ...
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This note was uploaded on 10/23/2010 for the course AST 47700 taught by Professor Wheeler during the Fall '10 term at University of Texas.
- Fall '10