Eight-meter-wavelength Transient Array (ETA)

Glossary of Science Terms

Big Bang
The Big Bang is the name given to the currently most widely accepted model of the initial stages of the universe, and it's subsequent evolution with time. Often, the term refers to the earliest stages of the expansion of the universe when the density and temperature of the universe would have been much higher than they are now. Ever since the earliest times the universe has been expanding (e.g., the average distance between galaxies has been increasing), and cooling (the temperature of the remnant radiation from the hot, dense, early times has been dropping). More.
black hole
A black hole is a theoretical construct of the general theory of relativity, where mass is contained in a small enough volume to produce a gravitational field strong enough to prevent the escape of light ("black"), and to produce a (spherical) trap which would ensnare anything, or anyone, unlucky enough to enter ("hole"). A black hole may result when the core of a sufficiently massive star collapses at the end of the star's thermomuclear burning stages (at the end of its normal lifetime). A supermassive black hole is thought to lie at the center of an active galaxy (e.g., radio galaxy, quasar), and many normal galaxies; small mass black holes might have been produced during the Big Bang ("primordial black holes"). Some early attempts to reconcile general relativity (a non-quantum-mechanical theory) with quantum mechanics have suggested that a black hole can slowly "evaporate" --- shrink, while spitting out mass --- over time. Such evaporation would proceed faster as the mass of the black hole became smaller resulting in an energetic burst of output at the end of the process. More.
Epoch of Reionization
According to the Big Bang model of the universe, the early universe was dense, of high temperature, and ionized --- the atoms were separated into their consituent nuclei and electrons. As the universe expanded and cooled the atoms could recombine (become neutral as the electrons were captured by the nuclei) at some 380,000 years after the beginning. Stars could then form subsequently and these early stars, through their ultraviolet radiation, could reionize the universe --- at the Epoch of Reionization. More.
A unit of energy, equivalent to 1 gram(centimeter/second)^2. One erg is only 1-ten-millionth of a Joule (the emission of 1 Joule of energy per second is equivalent to 1 Watt).
gamma-ray burst
A short, intense burst of gamma radiation coming from a highly localizable, random direction. These emission events are constrained by observations to have occurred outside the solar system, most likely at large distances ("cosmological distances") but the source of such events remains unknown. Gamma-ray bursts occur several times each day. More.
intergalactic medium
The very low density medium of gas, magnetic fields, and high energy particles in the space between the galaxies. More.
Lorentz factor
A parameter that signifies the extent to which relativistic effects come into play. Specifically, the Lorentz factor is equivalent to the inverse of the square-root of 1-(v^2/c^2), where v is the speed of motion of an object and c is the speed of light. In the context of the emission of radiation, greater Lorentz factors imply more compressed beaming of radiation along the direction of motion and thus greater intensity. More.
neutron star
A compact stellar object containing roughly the mass of the Sun, but compressed into an object about 10 miles across. Such objects have nearly the same mass density as a nucleus, and are composed mainly of neutrons. More.
A unit of distance equivalent to about 3.09 x 10^18 centimeters. The abbreviation for parsec is pc. 1 Mpc = 1 million parsecs. More.
A pulsating radio source. A typical pulsar has a pulse period of just less than one second, and a pulse width of a few percent of the pulse period. The shortest known pulsar has a period of 1.6 milliseconds; the longest known pulsar period is about 8.5 seconds. The pulse periods of pulsars remain very nearly constant over long periods of time (although increasing slightly over time). It is well accepted that pulsars are rotating neutron stars, and the pulse period equals the rotation period of the star. While the pulse emission mechanism is not well understood, the basic, most widely accepted model has the emission originating at or near the magnetic polar cap(s) of the highly magnetized rotating neutron star, and escaping along a relatively narrow "beam" pointing away from the magnetic polar cap. The magnetic axis is tipped with respect to the rotation axis, and therefore the "lighthouse beam" emitted by the pulsar sweeps the Earth once every rotation period (if the pulsar is oriented favorably). More.
radio telescope
An antenna (or set of antennas) designed, in conjuction with receivers, to detect and record the radio wavelength emissions of astrophysical phemomena. These instruments are typically much more sensitive than the common radio, but do have many similar features. Often a radio telescope looks superficially like a satellite dish (perhaps a large one), or a set of such dishes, but other radio telescopes do not. More.
The shift of emitted wavelengths of radiation toward longer wavelengths, caused, in the cosmological setting, by the expansion of the universe between the emission event and the observation (reception) of the radiation at Earth. Larger redshifts are associated with events in the more distant past (and therefore farther away from us). In cosmology, the redshift is represented by the letter z. More.
A supernova (Type II) is the explosive event that occurs when the core of a massive star collapses at the end of that star's lifetime. The resulting expansion of the star's outer layers and the subsequent release of radiation, can be produce an event in the optical spectrum equivalent in brightness to an entire galaxy. A Type I supernova occurs in a binary star system containing a white dwarf star which acquires enough material from the companion star to undergo thermonuclear detonation. More.
white dwarf
One of three possible compact object end points of stellar evolution. A white dwarf star contains roughly the mass of the Sun, compacted into an object the size of the Earth. Other compact objects are neutron stars and black holes. More.

NSF Acknowledgment and Disclaimer

This material is based upon work supported by the National Science Foundation under Grant No. AST-0504677. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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