29:50 Modern Astronomy
Fall 2002
Lecture 20...October 28, 2002
Neutron Stars
(1) Predictions of our understanding of the end of the road for a massive star. 4 attributes.
(2) Neutron Stars...historical preliminaries.
(3) Discovery of Pulsating Radio Sources (Pulsars) in 1968.
Short interlude on radio astronomy...picture of Parkes radio telescope
Diagram showing observations.
Periods of pulsars are extremely precise. The period for the pulsar 0329+54 is listed as P=0.71451866398 seconds, and every one of those digits counts. The periods of pulsars are so precise that they can be used for high quality clocks.
(4) Only explanation that worked...rotating neutron star
See Figure 20.19 of textbook. The fact that neutron stars turned out to be these clock-like rotators, emitting brilliant beams of radio emission, was totally unanticipated. It is a good example of how nature usually turns out to be stranger than our imagination.
(5) The clincher...1969- discovery of the Crab Nebula pulsar. apod/ap010602.html...Crab Nebula pulsar, and pulsar with a period of 0.033 seconds.
(6) Pulsars today...the sky is filled with them. There are approximately 1500 cataloged. Each one is the result of the unbelievably violent collapse of a massive star, and the resultant gigantic explosion. The Sky in Pulsars.
(7) Amazing facts about pulsars...
(a) They have periods from 1.6 milliseconds to 5 seconds.
(b) All of them are observed to slow down over time. Manchester's P-Pdot diagram. We estimate they last about 10 million years from the time they are born to the time they reach the ``death line''.
You can see them in X-rays, too Neutron Star in Puppis A Supernova Remnant.
(8) In about 35 years, neutron stars went from extremely exotic predictions of theoretical physics to extremely common (although certainly bizarre) astronomical objects.
(9) ``Pollution of the Interstellar Medium''. Every time a supernova explodes, it blasts several solar masses worth of heavy elements back into the interstellar medium, the gas from which stars form. This has been going on for the 13-15 billion year history of the universe.
Question: How would we go about verifying this? Transparency.
(10) But wait...there's more. I described ``neutron degeneracy pressure'' as a ``hard floor'' that stops a massive star's core collapse. But look at Figure 20.17 in the book.
Question: What does it mean?
