Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Cold fusion wikipedia , lookup
Nuclear fusion–fission hybrid wikipedia , lookup
Inertial confinement fusion wikipedia , lookup
Nuclear binding energy wikipedia , lookup
Muon-catalyzed fusion wikipedia , lookup
Inertial electrostatic confinement wikipedia , lookup
Atomic nucleus wikipedia , lookup
Stellar Evolution Bret Betz, Nick Jones, Calvin Schildknecht Formation of a Star • Begins with a Nebula- cloud of gas and dust http://ftp.seds.org/pub/images/hst/M16WF2.jpg • the density of one region of gas becomes great enough it begins to contract into a ball under the force of gravity. • Gravitational energy is converted into thermal energy. • As mass increases in one region the ball of gases begins to rotate. Formation of a Star (cont.) • Temperature and pressure increase and as mass accretion begins (mass falling to center) a protostar is formed. • Protostar- infant quasistar which glows in infrared spectrum and is on the fringe of the H.-R. diagram. Hertzsprung - Russell Diagram • Hertzsprung - Russell Diagram – graph of absolute luminosity (J/s) v. surface temperature (K) • Main sequence is where 90% of stars fall on the H.-R. diagram. Luminosity versus Brightness • Hertzsprung - Russell Diagram – graph of absolute luminosity (J/s) v. surface temperature (K) • Main sequence is where 90% of stars fall on the H.-R. diagram. Fusion in a Newborn Star • (Back to the protostar)… mass accretion stops and a “core” is formed. • When kinetic energy is sufficiently high, coulomb repulsion that keeps the hydrogen nuclei apart can be overcome and nuclear fusion can take place. • Hydrostatic equilibrium (outward force of fusion balances gravitational inward force) occurs—a star is born. Fusion in Our Sun • Proton-proton cycle: four protons fuse to form a 42He nucleus with the release of g rays and neutrinos. • Requires temperature of 107 K • When most of the H has been fused into He in the core, there is no longer sufficient energy to prevent gravitational forces from causing the core to heat up and contract. • The core contracts while outer regions are pushed out and a red giant is formed. • http://zebu.uoregon.edu/textbook/images1/pms. gif Fusion in Our Sun (cont.) • When the temperature in a red giant reaches 108 K (due to the core contracting) He nuclei begin to undergo fusion themselves. • 3 42He 126C • This is known as nucleosynthesis • The star moves to the horizontal branch of the H.-R. diagram. Fusion and Nucleosynthesis • Nucleosynthesis – the formation of heavy nuclei from lighter ones by means of fusion. • Cannot fuse nuclei heavier than 5626Fe and 56 Ni…yet. 28 • The star fuses the remaining elements and cools to become a white dwarf. What Else Can Happen to a Red Giant? • If more massive stars, more elements can be fused (C-Ne-O-Si–Fe) , red giant becomes larger. • Fe core is formed and when the temperature gets hot enough, photodisintegration (nuclei break up) occurs, and the core collapses. • 1s = core the size of earth to 10km radius of neutrons. Inverse beta decay- P + e- = n (gravity) • Outer layers, strike core, rebounds = supernova explosion. After Supernova - Heavier elements are created. - Large fraction of star is disbursed, enriching the universe. - Most known elements are created. Remnants of Supernova • After supernova, depending on mass: • Neutron Star- theoretical object neutrons, which has large B-field, very high mass. • Black Hole- (discussed earlier) Bibliography • http://zebu.uoregon.edu/textbook/images1/ pms.gif • http://ftp.seds.org/pub/images/hst/M16WF 2.jpg