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Chapter 13 The Bizarre Stellar Graveyard Chapter 13 The Bizarre Stellar Graveyard

White Dwarfs. . . n. . . are stellar remnants for low-mass stars. n. 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 B is a white dwarf star Sirius B is a white dwarf star

Sirius A And Sirius B In X-ray Sirius A Sirius B Sirius A And Sirius B In X-ray Sirius A Sirius B

Novas and Supernovas n Nova - a stellar explosion n Supernova - a stellar 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

Close Binary Systems and Mass Transfer Close Binary Systems and Mass Transfer

Nova March 1935 Herculis May 1935 Nova March 1935 Herculis May 1935

Diagram of nova process Diagram of nova process

A nova occurs when hydrogen fusion ignites on the surface of a white dwarf A nova occurs when hydrogen fusion ignites on the surface of a white dwarf star system Nova T Pyxidis (HST)

Light Curve of typical Nova Light Curve of typical Nova

Semidetached Binary System With White Dwarf Star (may result in a white dwarf (type 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 Type II Supernova n The star releases more energy in a just a few minutes than it did during its entire lifetime. » Example: SN 1987 A 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.

On July 4, 1054 astronomers in China witnessed a supernova within our own galaxy. On July 4, 1054 astronomers in China witnessed a supernova within our own galaxy. The remnant of this explosion is The Crab Nebula

Supernova 1987 a Supernova 1987 a

Type I and Type II Supernova Type I and Type II Supernova

Supernova Light Curves Supernova Light Curves

Hydrogen and Helium Burning Hydrogen and Helium Burning

Carbon Burning and Helium Capture Carbon Burning and Helium Capture

Still heavier elements are created in the final stages of life of massive stars 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. Alpha Process – Helium Capture produces heavier elements up to Fe and Ni.

Elements beyond Fe and Ni involve neutron capture. This forms unstable nuclei which then Elements beyond Fe and Ni involve neutron capture. This forms unstable nuclei which then decay into stable nuclei of other elements Formation of Elements beyond Iron occurs very rapidly as the star approaches supernova.

n The supernova explosion then distributes the newly formed matter throughout the interstellar space 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. . . 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. 4 M )

Relative Sizes Earth White Dwarf Neutron Star Relative Sizes Earth White Dwarf Neutron Star

Pulsars n n The first pulsar observed was originally thought to be signals from Pulsars n n The first pulsar observed was originally thought to be signals from extraterrestrials. (LGM-Little Green Men was their first designation) Period = 1. 337301 seconds exact! ~ 20 seconds of Jocelyn Bell’s data- the first pulsar discovered

n It was later shown to be unlikely that the pulsar signal originated from 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 Pulsars n The pulsing star inside the Crab Nebula was a pulsar. n Pulsars are rotating, magnetized neutron stars.

The Crab Nebula The Crab Nebula

The Crab Pulsar Period = 0. 033 seconds = 33 milliseconds The Crab Pulsar Period = 0. 033 seconds = 33 milliseconds

Light House Model – Beams of radiation emanate from the magnetic poles. – As 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.

Rotating Neutron Star Rotating Neutron Star

Light House model of neutron star emission accounts for many properties of observed Pulsars Light House model of neutron star emission accounts for many properties of observed Pulsars

Artistic rendering of the light house model Artistic rendering of the light house model

Rotation Rates of Pulsars n The neutron stars that appear to us as pulsars 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

Neutron –Star Binaries Neutron –Star Binaries

Mass Limits n Low mass stars – Less than 8 M on Main Sequence 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. 4 M < 3 M ) » Neutron Degeneracy Pressure

Black Holes n. . . are stellar remnants for high-mass stars. – i. e. 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 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 In general Relativity, space, time and mass are all interconnected

Space-Time No mass Distortion caused by mass Space-Time No mass Distortion caused by mass

Predictions of General Relativity n Advance of Mercury’s perihelion n Bending of starlight Predictions of General Relativity n Advance of Mercury’s perihelion n Bending of starlight

Advance of Mercury’s Perihelion 43” per century not due to perturbations from other planets Advance of Mercury’s Perihelion 43” per century not due to perturbations from other planets

Bending of Starlight 1. 75” Apparent position of the star Sun Light from star Bending of Starlight 1. 75” Apparent position of the star Sun Light from star bent by the gravity of the Sun

Schwarzschild Black Hole Event Horizon Rs = 3(Mass) + Rs Singularity Mass Rs 3 Schwarzschild Black Hole Event Horizon Rs = 3(Mass) + Rs Singularity Mass Rs 3 M 9 km 5 15 10 30

Near a Black Hole Near a Black Hole

What Can We Know? n Mass – gravity n Charge – Electric Fields n What Can We Know? n Mass – gravity n Charge – Electric Fields n Rotation Rate – Co-rotation

How Can We Find Them? n Look for X-ray sources – Must come from How Can We Find Them? n Look for X-ray sources – Must come from compact source » White Dwarf » Neutron Star » Black Hole – Differentiate by Mass » WD - < 1. 4 M » NS - between 1. 4 and 3 M » BH - > 3 M

Cygnus X-1 Cygnus X-1

End of Chapters End of Chapters

End of Section. End of Section.

Nucleosynthesis Evolutionary Time Scales for a 15 M Star Nucleosynthesis Evolutionary Time Scales for a 15 M Star

Energy Budget H He C Fusion Stages Fe Energy Budget H He C Fusion Stages Fe

Anazasi Pictographs Anazasi Pictographs

Supernova 1998 S in NGC 3877 Supernova 1998 S in NGC 3877

Supernova Remnants Tycho’s SNR - 1572 Supernova Remnants Tycho’s SNR - 1572

PSR 0628 -28 PSR 0628 -28

LGM? n Several more found at widely different places in the galaxy n Power LGM? n Several more found at widely different places in the galaxy n Power of a power equals total power potential output of the Earth n No Doppler shifts PULSARS

Light Time Argument n An object which varies its light can be no larger Light Time Argument n An object which varies its light can be no larger than the distance light can travel in the shortest period of variation.

To Darken the Sun Time Delay = Radius/c 500, 000 km/300, 000 km/s = To Darken the Sun Time Delay = Radius/c 500, 000 km/300, 000 km/s = 1. 67 sec

Only candidates: White Dwarfs, Neutron Stars Only candidates: White Dwarfs, Neutron Stars

Pulse Mechanisms F Binary Stars - How quickly can two stars orbit? 3 Two Pulse Mechanisms F Binary Stars - How quickly can two stars orbit? 3 Two WD about 1 m 3 Two NS about 1 s. 3 Neutron Stars in orbit should emit gravity waves which should be detectable. F Oscillations - Depends only on density 3 WD about ten seconds 3 NS about. 001 s Little variation permitted. F Rotation - Until the object begins to break up. 3 WD about 1 s 3 NS about. 001 s with large variation.

SS 433 SS 433

Synchrotron Radiation Magnetic lines of force Electron Synchrotron Radiation Magnetic lines of force Electron

Glitches Glitches