Copyright © 2010 Pearson Education, Inc. Chapter 13 Neutron Stars
Copyright © 2010 Pearson Education, Inc. Chapter 13 Neutron Stars and Black Holes
Copyright © 2010 Pearson Education, Inc. Units of Chapter Neutron Stars Pulsars Neutron Star Binaries Gamma-Ray Bursts
Copyright © 2010 Pearson Education, Inc. After a Type I supernova, little or nothing remains of the original star. After a Type II supernova, part of the core may survive. It is very dense – as dense as an atomic nucleus – and is called a neutron star.supernova Neutron Stars
Copyright © 2010 Pearson Education, Inc. Discovery! In 1934 Walter Baade and Fritz Zwicky proposed the existence of the neutron star, only a year after the discovery of the neutron by Sir James Chadwick.
Copyright © 2010 Pearson Education, Inc. Neutron stars, although they have 1-3 solar masses, are so dense that they are very small. This image shows a 1-solar-mass neutron star, about 10 km in diameter, compared to Manhattan. Neutron Stars
Copyright © 2010 Pearson Education, Inc. White Dwarf A white dwarf of 1 solar mass is the size of Earth. 10,000 km Neutron Star White Dwarf and Neutron star have the same mass
Copyright © 2010 Pearson Education, Inc. Other important properties of neutron stars (beyond mass and size): Rotation – as the parent star collapses, the neutron core spins very rapidly, conserving angular momentum. Typical periods are fractions of a second. (Fastest 43,000 rpm) Magnetic field – again as a result of the collapse, the neutron star’s magnetic field becomes enormously strong. Neutron Stars
Copyright © 2010 Pearson Education, Inc. How To Gain Weight The gravitational field at a neutron star’s surface is about 2×10 11 times stronger than on Earth 200,000,000,000 one teaspoon (5 milliliters) of its material would have a mass over 5.5×10 12 kg
Copyright © 2010 Pearson Education, Inc. What’s Inside?
Copyright © 2010 Pearson Education, Inc. Quantum Physics Pauli exclusion principle. This principle states that no two neutrons (or any other fermionic particles) can occupy the same place and quantum state simultaneously. Wolfgang Pauli
Copyright © 2010 Pearson Education, Inc. What is a Neutron? Can be thought of as a proton which has merged with an electron. The positive charge of the proton plus the negative charge of an electron yields zero net charge.
Copyright © 2010 Pearson Education, Inc. Neutrons Neutrons have no electrical charge Neutrons do not need to overcome any Coulomb barrier 1.675×10 −27 kg Lifetime seconds
Copyright © 2010 Pearson Education, Inc. How Many and Where? About 2000 neutron stars in the Milky Way galaxy Often detected as radio pulsars Pulsars were discovered by Jocelyn Bell in 1967 Predicted by J. Robert Oppenheimer in 1938
Copyright © 2010 Pearson Education, Inc. The first pulsar was discovered in It emitted extraordinarily regular pulses; nothing like it had ever been seen before. After some initial confusion, it was realized that this was a neutron star, spinning very rapidly. Pulsars
Copyright © 2010 Pearson Education, Inc. a) extremely rapid rotation. b) high-temperature fusion reactions. c) a narrow regular pulse of radiation. d) high-speed motion through the galaxy. e) an intense magnetic field. Question 1 Pulsars usually show all of the following EXCEPT
Copyright © 2010 Pearson Education, Inc. Question 1 Pulsars usually show all of the following EXCEPT Pulsars are neutron stars no longer undergoing fusion in their cores. a) extremely rapid rotation. b) high-temperature fusion reactions. c) a narrow regular pulse of radiation. d) high-speed motion through the galaxy. e) all of the above.
Copyright © 2010 Pearson Education, Inc. But why would a neutron star flash on and off? This figure illustrates the lighthouse effect responsible. Strong jets of matter are emitted at the magnetic poles, as that is where they can escape. If the rotation axis is not the same as the magnetic axis, the two beams will sweep out circular paths. If Earth lies in one of those paths, we will see the star blinking on and off. Pulsars Pulsar Crab Nebula
Copyright © 2010 Pearson Education, Inc. a) pulsars can be used as interstellar navigation beacons. b) the period of pulsation increases as a neutron star collapses. c) pulsars have their rotation axis pointing toward Earth. d) a rotating neutron star generates an observable beam of light. Question 3 The lighthouse model explains how
Copyright © 2010 Pearson Education, Inc. Question 3 The lighthouse model explains how a) pulsars can be used as interstellar navigation beacons. b) the period of pulsation increases as a neutron star collapses. c) pulsars have their rotation axis pointing toward Earth. d) a rotating neutron star generates an observable beam of light.
Copyright © 2010 Pearson Education, Inc. Pulsars radiate their energy away quite rapidly; the radiation weakens and stops in a few tens of millions of years, making the neutron star virtually undetectable. Pulsars also will not be visible on Earth if their jets are not pointing our way. All Pulsars are neutron stars but not all neutron stars are pulsars. Pulsars
Copyright © 2010 Pearson Education, Inc. There is a pulsar at the center of the Crab Nebula; the images to the right show it in the “off” and “on” positions. Pulsars
Copyright © 2010 Pearson Education, Inc. The Crab pulsar also pulses in the gamma ray spectrum, as does the nearby Geminga pulsar. Pulsars
Copyright © 2010 Pearson Education, Inc. An isolated neutron star has been observed by the Hubble telescope; it is moving rapidly, has a surface temperature of 700,000 K, and is about 1 million years old. Pulsars
Copyright © 2010 Pearson Education, Inc. Bursts of X rays have been observed near the center of our Galaxy. A typical one appears at right, as imaged in the X-ray spectrum. Neutron Star Binaries
Copyright © 2010 Pearson Education, Inc. These X-ray bursts are thought to originate on neutron stars that have binary partners. The process is very similar to a nova, but much more energy is emitted due to the extremely strong gravitational field of the neutron star. Neutron Star Binaries
Copyright © 2010 Pearson Education, Inc. Most pulsars have periods between 0.03 and 0.3 seconds, but a new class of pulsar was discovered in the early 1980s: the millisecond pulsar. Neutron Star Binaries
Copyright © 2010 Pearson Education, Inc. Millisecond pulsars are thought to be “spun-up” by matter falling in from a companion. This globular cluster has been found to have 108 separate X-ray sources, about half of which are thought to be millisecond pulsars. Neutron Star Binaries X-ray Binary
Copyright © 2010 Pearson Education, Inc. Gamma-ray bursts also occur, and were first spotted by satellites looking for violations of nuclear test-ban treaties. This map of where the bursts have been observed shows no “clumping” of bursts anywhere, particularly not within the Milky Way. Therefore, the bursts must originate from outside our Galaxy. Gamma-Ray Bursts
Copyright © 2010 Pearson Education, Inc. These are some sample luminosity curves for gamma-ray bursts. Gamma-Ray Bursts
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The Guts
Copyright © 2010 Pearson Education, Inc. HESS Telescope High Energy Spectroscopic System
Copyright © 2010 Pearson Education, Inc. Light Cone
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Cosmic Rays Mostly protons colliding with nitrogen Creates masons, muons, pions, electrons
Copyright © 2010 Pearson Education, Inc. Spark Chamber +HV - HV Cosmic ray
Copyright © 2010 Pearson Education, Inc. Pierre Auger Observatory
Copyright © 2010 Pearson Education, Inc. Distance measurements of some gamma bursts show them to be very far away – 2 billion parsecs for the first one measured. Occasionally the spectrum of a burst can be measured, allowing distance determination. Gamma-Ray Bursts
Copyright © 2010 Pearson Education, Inc. Two models – merging neutron stars or a hypernova – have been proposed as the source of gamma-ray bursts. Colliding BinariesColliding Binaries Gamma-Ray Bursts
Copyright © 2010 Pearson Education, Inc. a) matter spiraling into a large black hole. b) the collision of neutron stars in a binary system. c) variations in the magnetic fields of a pulsar. d) repeated nova explosions. e) All of the above are possible. Question 4 One possible explanation for a gamma-ray burster is
Copyright © 2010 Pearson Education, Inc. a) matter spiraling into a large black hole. b) the collision of neutron stars in a binary system. c) variations in the magnetic fields of a pulsar. d) repeated nova explosions. e) All of the above are possible. Question 4 One possible explanation for a gamma-ray burster is Gamma-ray bursts vary in length, and the coalescence of two neutron stars seems to account for short bursts.
Copyright © 2010 Pearson Education, Inc. This burst looks very much like an exceptionally strong supernova, lending credence to the hypernova model. Gamma-Ray Bursts
Copyright © 2010 Pearson Education, Inc. Supernova may leave behind neutron star. Neutron stars are very dense, spin rapidly, and have intense magnetic fields. Neutron stars may appear as pulsars due to lighthouse effect. Neutron star in close binary may become X-ray burster or millisecond pulsar. Gamma-ray bursts probably are due to two neutron stars colliding, or to hypernova. Summary of Chapter 13