The Fate of High-Mass Stars Chapter 11 The Fate of High-Mass Stars

11.1 Supernovas Nova - means “a new star” but are actually stellar explosions Supernova - a stellar explosion that marks the end of a star’s evolution Type I Supernovas - occur in binary systems in which one is a white dwarf

Type II Supernovas - occur when a massive star’s iron core collapses

Energy Budget Fe C He Energy H Fusion Stages

Type II Supernovae The star releases more energy in a just a few minutes than it did during its entire lifetime. Example: SN 1987A Brightness remains high for hundreds of days.

Supernova 1998S in NGC 3877

Type II Supernovae On July 4, 1054 astronomers in China witnessed a supernova within our own galaxy.

Type II Supernovae After the explosion of a massive star, a huge glowing cloud of stellar debris - a supernova remnant - steadily expands. Example: Crab Nebula

The Crab Nebula

Type II Supernovae 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.

Energy Output for Type I and Type II Type II Supernovae 1053 ergs total Of this 1051 ergs shows up at KE of the ejected shell and 1050 ergs as light. Most of the rest is in the escaping neutrinos! Type I supernovae are more energetic.

Relative sizes Earth White Dwarf Neutron Star

Neutron Stars ...are stellar remnants for medium-mass stars. ...are found in the centers of some type II supernova remnants. ...have diameters of about 6 miles. ...have masses greater than the Chandrasekhar mass.

The Crab Nebula

The Crab Pulsar

PSR 0628-28

Pulsars Pulsars are rotating, magnitized neutron stars. The pulsing star inside the Crab Nebula was a pulsar. 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

Pulsars The first pulsars observed was originally thought to be a signal from extraterrestrials. This was later shown to be unlikely after many other pulsars were found all over the sky. Also, it was found that each pulse had a total power output equal to that of all the resources of Earth.

Rotation Rates of Pulsars The neutron stars that appear to us as pulsars rotate about once every second. Before a star collapses to a neutron star it probably rotates about once every 25 days. Why is there such a big difference in rotation rates? Answer: Conservation of Angular Momentum

11.2.2 Rotation of Neutron Stars J = Angular Momentum I = Moment of Interia w = angular speed For a sphere...

Black Holes ...are stellar remnants for high-mass stars. i.e. those greater than 3 solar masses …have a gravitational attraction that is so strong that light cannot escape from it. …are found in some binary star systems and there may be super-massive black holes in the centers of some galaxies.

Cygnus X-1

End of Chapter 11

Supernova Remnants Tycho’s SNR - 1572

Core Remnant Too massive for electron degeneracy to halt collapse (> 1.4 M) Electromagnetic force Neutron Degeneracy can halt collapse M < 3 M Strong nuclear force Neutron Star

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

Glitches

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

SS 433