Presentation on theme: "Chapter 13 The Bizarre Stellar Graveyard White Dwarfs... n...are stellar remnants for low-mass stars. n...are found in the centers of planetary nebula."— Presentation transcript:
White Dwarfs... n...are stellar remnants for low-mass stars. n...are found in the centers of planetary nebula. n...have diameters about the same as the Earth’s. n...have masses less than the Chandrasekhar mass.
Sirius A And Sirius B In X-ray Sirius B Sirius A
Novas and Supernovas n Nova - a stellar explosion n Supernova - a stellar explosion that marks the end of a star’s evolution n White Dwarf Supernova (Type I supernova)- occur in binary systems in which one is a white dwarf n Massive Star Supernova (Type II Supernova) - occur when a massive star’s iron core collapses
Semidetached Binary System With White Dwarf Star (may result in a white dwarf (type I ) supernova)
Type II Supernova n The star releases more energy in a just a few minutes than it did during its entire lifetime. »Example: SN 1987A n After the explosion of a massive star, a huge glowing cloud of stellar debris - a supernova remnant - steadily expands. »Example: Crab Nebula n After a supernova the exposed core is seen as a neutron star - or if the star is more than 3 solar masses the core becomes a black hole.
The remnant of this explosion is The Crab Nebula On July 4, 1054 astronomers in China witnessed a supernova within our own galaxy.
Still heavier elements are created in the final stages of life of massive stars
Alpha Process – Helium Capture produces heavier elements up to Fe and Ni.
Elements beyond Fe and Ni involve neutron capture. Formation of Elements beyond Iron occurs very rapidly as the star approaches supernova. This forms unstable nuclei which then decay into stable nuclei of other elements
n The supernova explosion then distributes the newly formed matter throughout the interstellar space (space between the stars). n This new matter goes into the formation of interstellar debris. n The remnant core is a dense solid core of neutrons – a neutron star!
Neutron Stars n...are stellar remnants for high-mass stars. n...are found in the centers of some type II supernova remnants. n...have diameters of about 6 miles. n...have masses greater than the Chandrasekhar mass. (1.4M n...have masses greater than the Chandrasekhar mass. (1.4M )
Pulsars n The first pulsar observed was originally thought to be signals from extraterrestrials. n (LGM-Little Green Men was their first designation) ~ 20 seconds of Jocelyn Bell’s data- the first pulsar discovered Period = 1.337301 seconds exact!
n It was later shown to be unlikely that the pulsar signal originated from extraterrestrial intelligence after many other pulsars were found all over the sky.
Pulsars n The pulsing star inside the Crab Nebula was a pulsar. n Pulsars are rotating, magnetized neutron stars.
The Crab Pulsar Period = 0.033 seconds = 33 milliseconds
Light House Model –Beams of radiation emanate from the magnetic poles. –As the neutron star rotates, the beams sweep around the sky. –If the Earth happens to lie in the path of the beams, we see a pulsar.
Rotation Rates of Pulsars n The neutron stars that appear to us as pulsars rotate about once every second or less. n Before a star collapses to a neutron star it probably rotates about once every 25 days. n Why is there such a big change in rotation rate? n Answer: Conservation of Angular Momentum
Mass Limits n Low mass stars –Less than 8 M on Main Sequence –Become White Dwarf (< 1.4 M ) »Electron Degeneracy Pressure n High Mass Stars –Less than 100 M on Main Sequence –Become Neutron Stars (1.4M < M < 3M ) »Neutron Degeneracy Pressure
Black Holes n...are stellar remnants for high-mass stars. –i.e. remnant cores with masses greater than 3 solar masses n …have a gravitational attraction that is so strong that light cannot escape from it. n …are found in some binary star systems and there may be super-massive black holes in the centers of some galaxies.
Supermassive Stars n If the stellar core has more than three solar masses after supernova, then no known force can halt the collapse Black Hole Black holes were first predicted by the General Theory of Relativity, which is theory of gravity that corrects for some of the short-falls of Newton’s Theory of Gravity.
In general Relativity, space, time and mass are all interconnected
Pulse Mechanisms F Binary Stars - How quickly can two stars orbit? 3Two WD about 1 m 3Two NS about 1 s. 3Neutron Stars in orbit should emit gravity waves which should be detectable. F Oscillations - Depends only on density 3WD about ten seconds 3NS about.001 s Little variation permitted. F Rotation - Until the object begins to break up. 3WD about 1 s 3NS about.001 s with large variation.