* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Neutron Stars
Survey
Document related concepts
Aquarius (constellation) wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
X-ray astronomy wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Observational astronomy wikipedia , lookup
Gamma-ray burst wikipedia , lookup
Corvus (constellation) wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Timeline of astronomy wikipedia , lookup
H II region wikipedia , lookup
Star catalogue wikipedia , lookup
Future of an expanding universe wikipedia , lookup
Type II supernova wikipedia , lookup
Astrophysical X-ray source wikipedia , lookup
Astronomical spectroscopy wikipedia , lookup
Stellar kinematics wikipedia , lookup
Transcript
Neutron Stars Pulsars Neutron Stars In 1967, it was believed (by some) that the first intelligent signal from outer space had been discovered. A graduate student by the name of Jocelyn Bell observed highly periodic, well defined pulsations of electromagnetic energy. The pulses lasted 0.01 sec, and repeated regularly with a period of 1.34 sec. WOW Neutron Stars Bell’s thesis advisor, Anthony Hewish, explained the observation as being related to a small, rotating, radiating object. The object had to be undergoing regular rotation to explain the well-defined periodicity. The object had to be small in order to explain the sharpness of the emission (a large radiating object would would produce the radiation over a longer time). Neutron Stars The best current model explains the pulsations as being produced by a rotating neutron star. Neutron Stars The remnant of a type II supernova is a remarkably compact Neutron Star. Property Observation Nuclear Reactions Ceased Pressure Neutron Degeneracy Pressure Diameter About 20 km Density 1017 - 1018 Kg/m3 Note: density of an atomic nucleus is approximately 1017 Kg/m3 Neutron Stars The Pulsar Neutron Stars The Pulsar Neutron Stars Neutron Stars Lighthouse Model – the periodic emission of radiation as the pole of the neutron star rotates periodically into the view of the earth. Note: The reception of the pulsating radiation requires that the radiating “hot spot” be directed toward the earth. Otherwise, the pulsations will not be seen. Neutron Stars Some properties: * High velocities can be observed * Short period pulsations for some pulsars * X-ray bursters Neutron Stars High Speeds Doppler shift measurements show that many neutron stars are moving at very high speeds. Explanation: The KABLOOEY of the outer shells in the SN event exert a force back on the neutron core (Newton’s Third Law – For every action there is an equal and opposite reaction. Neutron Stars High Speeds Newton’s Third Law – For every action there is an equal and opposite reaction. Symmetric explosion The action reaction pair will not cause the star to move Neutron Stars High Speeds Newton’s Third Law – For every action there is an equal and opposite reaction. asymmetric explosion The action reaction pair will cause the star to move Neutron Stars High Speeds Newton’s Third Law – For every action there is an equal and opposite reaction. asymmetric explosion Velocity of ejected neutron star The action reaction pair will cause the star to move Neutron Stars Some properties: * High velocities can be observed * Short period pulsations for some pulsars * X-ray bursters Neutron Stars Millisecond Pulsar – a pulsar with a period an the order of a millisecond. 1 millisecond = 0.001 seconds In order for the pulsar of pulse at a period of 0.001 seconds, the neutron star must be rotating a thousand times a second ! Neutron Stars Explanation: Conservation of Angular Momentum: The angular momentum of a collapsing core must be conserved. For a rotating sphere, the angular momentum is given by L = I = 2/5 MR2 Where L is the angular momentum I = 2/5 MR2 is called the moment of inertia = 2R/T is the angular speed in radians/second or revolutions/second Neutron Stars Explanation: Conservation of Angular Momentum: The angular momentum of a collapsing core must be conserved. L = I = 2/5 MR2 = constant If R decreases as the core collapses, must increase Neutron Stars Neutron Stars Example: A star is rotating with = 1 rev/sec. If the core begins wit ha radius equal to the radius of the sun, and collapses to a final radius of 0.01 R, what will its final angular speed become after the collapse? Assume the mass stays a constant. Solution: use proportions L = I = 2/5 MR2 = constant Ri 2 i = Rf 2 f f = Ri Rf ( ) 2 i = (1/1000)i = 0.0001 rev/sec Neutron Stars Note: The shortest period pulsar is around 0.001 seconds (millisecond pulsar). Periods shorter than this do not exist (such as in the previous calculation) because the object would have to rotate so fast it would overcome gravity and fly apart. Neutron Stars Some properties: * High velocities can be observed * Short period pulsations for some pulsars * X-ray bursters Neutron Stars X-Ray Burster – Neutron star that experiences a large increase in luminosity, emitting radiation in the X-ray region of the electromagnetic spectrum. Explanation: The mechanism is basically the same as that of a nova. A neutron star that is part of a binary system will accrete material from the companion. Once enough material is accumulated o nthe surface of the neutron star, hydrogen fusion will occur. Neutron Stars X-Ray Burster – Neutron star that experiences a large increase in luminosity, emitting radiation in the X-ray region of the electromagnetic spectrum. Explanation: Because the gravity is so strong at the surface of the neutron star, compression will happen rapidly, and the fusion will occur violently, producing high energy photons. Recall E = hf, so high energy photons will have a very high frequency. Electromagnetic Wave Basics The Electromagnetic Spectrum Wavelength in meters 10000 1 .0001 10-8 IR Radio Microwave 10-12 X-Ray UV