Neutrino physics after the supernova.Neutrino neutrino (ntrē`nō) [Ital.,=little neutral (particle)], elementary particle with no electric charge and a very small mass emitted during the decay of certain other particles. physics after the supernova
Neutrinos from supernova 1987A arebeginning to change some of physicists' ideas about those elusive but important particles. The latest aspect of this is the attempt to determine whether the neutrino has mass by calculating from the time of flight between the Large Magellanic Cloud Noun 1. Large Magellanic Cloud - the larger of the two Magellanic Clouds visible from the southern hemisphere
Magellanic Cloud - either of two small galaxies orbiting the Milky Way; visible near the south celestial pole and the earth. What seems to be the first such calculation to be published--by John N. Bahcall John Norris Bahcall (December 30 1934 – August 17 2005) was an American astrophysicist. He is best known for his contributions to the solar neutrino problem and the development of the Hubble Space Telescope, and for his leadership and development of the Institute for Advanced of the Institute for Advanced Study in Princeton, N.J., and Sheldon L. Glashow of Harvard University--appears in the April 2 NATURE. When they first appeared in physics, neutrinos were not thought to have mass. More recently some theories have wanted them to have it. Now, from the supernova, it seems the original idea may have been right.
Supernova neutrinos may also helpchange astrophysicists' ideas of what happens in a supernova explosion. The usual theories propose that the core of the exploding star collapses--once--to become an ultradense object, either a neutron star neutron star, extremely small, extremely dense star, about double the sun's mass but only a few kilometers in radius, in the final stage of stellar evolution. Astronomers Baade and Zwicky predicted the existence of neutron stars in 1933. or a black hole. At the recent Heavenly Accelerators workshop, held at Johns Hopkins University Johns Hopkins University, mainly at Baltimore, Md. Johns Hopkins in 1867 had a group of his associates incorporated as the trustees of a university and a hospital, endowing each with $3.5 million. Daniel C. in Baltimore, Alvaro De Rujula of Boston University Boston University, at Boston, Mass.; coeducational; founded 1839, chartered 1869, first baccalaureate granted 1871. It is composed of 16 schools and colleges. proposed that instead of just one collapse there might be a series of such collapses in a single supernova, each leading to a denser state than the previous one.
The first observation of neutrinos fromthe supernova to be reported to be spoken of; to be mentioned, whether favorably or unfavorably.
See also: Report , which came from a European collaboration working with the NUSEX detector under Mt. Blanc on the French-Swiss border, seems not to fit the standing theory--the neutrinos appear much more energetic than they ought to be. The other two observations, simultaneous determinations by the Kamiokande detector at Kamioka, Japan, and the IMB IMB International Mission Board
IMB Irish Medicines Board
IMB International Maritime Bureau
IMB Institute for Molecular Bioscience (Brisbane, Australia)
IMB IndyMac Bank (Pasadena, CA) detector at Fairhaven, Ohio Fairhaven is an unincorporated community in eastern Israel Township, Preble County, Ohio, United States. It lies along State Route 177 at its intersection with Israel-Somers Road. , seem closer to theoretical expectations. Some commentators have suggested that the Mt. Blanc observation is mistaken; these neutrinos were not from the supernova. De Rujula supposes the Mt. Blanc observation is real and combines it with the two others to see what the combination might tell about what happens in a supernova.
The Mt. Blanc detector saw five pulsesof neutrinos in 7 seconds, and it saw them 4 hours 43 minutes before the simultaneous observations of Kamiokande and IMB. De Rujula makes a statistical argument to support the idea that Mt. Blanc saw something real, but then he has to explain why Kamiokande saw nothing at the time of the Mt. Blanc events. He can accomplish this by assuming that the energy of the neutrinos was somewhat less than observers have generally been postulating. Then, taking account of the characteristics of the detectors, he can make the different experiments compatible with one another. Thus he comes to the conclusion that there were two bursts of neutrinos from the supernova, 4 hours 43 minutes apart, and that leads to his suggestion of a double collapse.
Theory supposes that the collapse ofthe core of a star initiates a supernova explosion. During a star's life, heat produced by thermonuclear ther·mo·nu·cle·ar
1. Of, relating to, or derived from the fusion of atomic nuclei at high temperatures: thermonuclear reactions.
2. fusion processes holds it up, preventing it from collapsing under its own gravity. When a supernova begins, that support somehow fails and the core of the star collapses, producing either a neutron star or a black hole. An outward flying flux of neutrinos is a by-product by·prod·uct or by-prod·uct
1. Something produced in the making of something else.
2. A secondary result; a side effect.
1. of the collapse.
The core collapse also triggers a shockwave that propagates outward, blowing away the outer layers of the star. De Rujula calculates that it would take about 10 hours for the shock to cover the distance to the outermost out·er·most
Most distant from the center or inside; outmost.
furthest from the centre or middle
Adj. 1. layers of the star, and he proposes that--at least in the case of supernova 1987A--the shock didn't get all the way to the surface. A fizzling-out of the shock would have caused a second collapse of the core. The first collapse would have made a neutron star; the second would have made a denser object, a black hole. The experiments on earth would have received bursts of neutrinos from both collapses, separated by the 4 hours 43 minutes.
If this is really what happened, and ablack hole is now there, De Rujula says, there should now be a steady flux of neutrinos from matter accreting around the black hole drawn by its tremendous gravity. He pleads that the detectors be kept on to look for this steady flux. Unfortunately, Kamiokande has already been shut down for maintenance and improvements.
Neutrinos from the supernova shouldcome to us at the speed of light so long as they have no rest mass. Edward Kolb Edward W. Kolb, usually known as Rocky Kolb, is a cosmologist at Fermi National Accelerator Laboratory and a professor at the University of Chicago. He has worked on many aspects of the big bang cosmology, including baryogenesis, nucleosynthesis and dark matter. of Fermi National Accelerator Laboratory Fermi National Accelerator Laboratory (Fermilab), physical science research center located near Batavia, Ill., est. 1968 as the National Accelerator Laboratory, renamed 1974 in honor of Enrico Fermi. It was built on the site of the former village of Weston. in Batavia, Ill., speaking at the Heavenly Accelerators workshop, calculated the duration of the flight at about 5 trillion seconds (5.36 0.5210(12) seconds). If the neutrinos have a small rest mass, they cannot come quite at the speed of light. The flight time of a given neutrino will be a little longer than that, and those with higher energy will come fastest. The duration of the pulses as they arrive at earth will depend on the amount of this supposed neutrino rest mass.
When the existence of neutrinos wasfirst postulated, they were supposed to have exactly zero rest mass, and most experiments have been consistent with zero rest mass. The exceptions have been some experiments in the Soviet Union that persist in Verb 1. persist in - do something repeatedly and showing no intention to stop; "We continued our research into the cause of the illness"; "The landlord persists in asking us to move"
continue showing a neutrino rest mass of 30 or 40 electron-volts (eV). Some of the recent theories that are trying to unite all of particle physics particle physics
or high-energy physics
Study of the fundamental subatomic particles, including both matter (and antimatter) and the carrier particles of the fundamental interactions as described by quantum field theory. in a single framework need to have neutrinos with a small rest mass, and these theories have spurred both the Russian and other attempts to find one. In addition, if neutrinos have a small rest mass, cosmologists can say that large gangs of them floating through the universe would constitute the majority of the matter in the universe and would provide enough unseen matter to make the universe close on itself, a condition that many cosmological theories need to have.
Unfortunately for these people,Bahcall and Glashow state that their analysis of the supernova data shows that neutrinos probably have no rest mass, or at least no more than 11 eV. This limit on the rest mass, they say, is stronger than any that has been achieved in 50 years of terrestrial experiments. The exact limit that one can set on a possible neutrino rest mass depends on certain assumptions about the relation of the duration of the neutrino pulses at earth to their duration at the source. Kolb, reviewing several yet-unpublished papers on the subject, says they set various limits from 5 eV to 25 eV.
If the supernova data are showing thatneutrinos have zero rest mass, that, as De Rujula comments, "in 2 seconds would have destroyed 20 years of work by the Russians.' It would also drive a nail into the coffin of some of the proposed unified theories of particle physics, and, to quote Bahcall and Glashow, "confirms the view that electron neutrinos do not constitute the major component of the matter density of the universe.'