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
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.
- 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
- 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
- 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.
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
ETA Science Primer