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A transverse wave that occurs in a region containing a magnetic field and a plasma. The ionized and therefore highly conducting plasma is said to be “frozen in” to the magnetic field and is forced to take part in its wave motion. The existence of these waves was predicted by Hannes Olof Gosta Alfvén in 1942— this work inaugurated the study of magnetohydrodynamics for which Alfvén was awarded the Nobel Prize in 1970. SeeMagnetohydrodynamics.
A helium-4 nucleus emitted by a larger nucleus during a type of radioactive decay known as alpha decay. An alpha particle consists of two protons and two neutrons.
The Pierre Auger Observatory project, an international effort to study the highest-energy cosmic rays. Two giant detector arrays, each covering 3,000 km2, will be constructed in the Northern and Southern Hemispheres. Each will consist of 1,600 particle detectors and an atmospheric fluorescence detector. The objective of the arrays is to measure the arrival direction, energy, and mass composition of cosmic-ray air showers above 1019 eV.
A class of subatomic particles that includes the proton and neutron. Baryons are a subclass of the class of particles known as hadrons that interact via the strong interaction. Baryons have half-integral spin.
Berkeley Illinois Maryland Association Array (BIMA):
A consortium consisting
of the Radio Astronomy Laboratory at the University of California, Berkeley; the Laboratory for Astronomical Imaging at the University of Illinois, Urbana; and the Laboratory for Millimeter-Wave Astronomy at the University of Maryland. BIMA operates a millimeter-wave radio interferometer at Hat Creek, California, with support from the National Science Foundation.
As an energetic electron slows down in a material, it emits photons via bremsstrahlung. At high electron energies, these photons can be reconverted back to electron-positron pairs. The Bethe-Heitler process describes the bremsstrahlung emitted by an electron in a coulomb field.
Thermally produced electron-positron plasmas are thought to play an important role in the evolution of the cores of massive stars, neutron-star and black-hole accretion disks, pulsars, quasars, astrophysical gamma-ray bursters, and in the big bang. In the past few years, discoveries of intense, broadened 511-keV annihilation lines from several galactic black-hole candidates suggest that, in addition to transient-pair production, steady-state thermal pair plasmas exist. Since pairs annihilate on short time scales, maintaining such steady-state conditions requires the copious production of pairs in order to balance the annihilation rate. Such pair-balanced steady-state plasmas represent a new state of matter, with unique radiative and thermodynamic properties. For a plasma to be in a steady state, the heating rate must be balanced by the cooling rate, which consists of bremsstrahlung, inverse Compton scattering, and pair