Physics and the Universe 1080 Test 3
Time Dilation
A difference of elapsed time between two events as measured by observers either moving relative to eachother or differently situated from a gravitational mass
Ring Galaxies
A galaxy having the shape of an elliptical ring thought to be result of a collision of two galaxies
Seyfert Galaxies
A galaxy of a type characterized by a bright compact core that shows strong infrared emission
Protostellar Disk
A gas cloud around a forming star is flattened by rotation
Light Curve
A graph of light intensity of a celestial object of region
H-R Diagrams
A graph of stars showing the relationship between the stars' absolute magnitudes versus their spectral classifications or effective temperatures.
Galactic Cannibalism
A large galaxy results in a larger galaxy through tidal gravitational interactions with a companion
Filaments
A long structure of a relatively cool material in the solar corona
Quasars
A massive and extremely remote celestial object emitting exceptionally large amounts of energy, star like image in telescope
Spectroscopic Parallax
A method for measuring the distance to stars
Triple-alpha Process
A nuclear fushion reaction in which three helium nuclei fuse to form a carbon nucleus thereby releasing energy
Rotation Curve
A plot of the measured magnitude of the orbital velocities of visible stars
Blackhole
A region of space having a gravitational field so intense that no matter or radiation can escape
Dark Energy
A repulsive force that counteracts gravity and causes the universe to expand at an accelerating rate
Accretion Disk
A rotating disk of matter formed by accretion around a massive body under the influence of gravitation
Main Sequence
A series of star types to which most stars belong
Herbig- Haro Objects
A small clump of emission nebulosity formed where jets of matter used to stream from newly formed stars and smashed into interstellar gas
Nova
A star showing a sudden large increase in brightness and then slowly returning to its original state over a few months
Supernova
A star that suddenly increases greatly in brightness because of catastrophic explosion that ejects most of its mass
Binary Stars
A system of two stars bound together by gravity and orbiting a common center of mass
Cepheids
A variable star having a regular cycle of brightness with a frequency related to its luminosity
Spiral Density Wave Theory
A wave that moves through the disk causing the stars and gas to clump up along the wave
GUT
Any number of theories designed to explain gravitational,electromagnetic, strong &weak interactions in terms of a single math formalism
Spectral Class
Any of various groups into which stars are classified according to characteristic spectral lines and bonds
Absorption Lines
Appears in a spectrum if an absorbing material is placed between a source and the observer. This material could be the outer layers of a star, a cloud of interstellar gas or a cloud of dust.
Emission Lines
Appears in a spectrum if the source emits specific wavelengths of radiation. This emission occurs when an atom, element or molecule in an excited state returns to a configuration of lower energy.
Elliptical Galaxy
Approximately ellipsoidal shape and smooth nearly featureless brightness profile
Event Horizon
Boundary around a black hole beyond which no light or other radiation can escape
Helium Flash
Brief thermal runaway nuclear fushion of large quantities of helium into carbon.
Luminosity
Brightness of a celestial object
Apparent Magnitude
Brightness of a star to an observer on Earth
Pulsar
Celestial object thought to be a rapidly rotating neutron star that emits regular pulse of radio waves
Halo
Circle of white or colored light around the sun,moon, or other luminous body caused by refraction through ice crystals in the atmosphere
Standard Candle
Class of objects whose distances can be computed by comparing their observed brightness with known luminosity
Degenerate Matter
Collection of free, non-interacting particles with a pressure and other physical characteristics
Hubble Constant
Constant indicative (showing) of the rate of expansion of the universe that is used in relating the apparent velocity of recession of a distant galaxy and its distance
Molecular Clouds
Cool, dense interstellar region composed of a wide variety of molecules, mainly hydrogen &dust, in which stars form.
Nucleosynthesis
Cosmic formation of atoms more complex than the hydrogen atom
Stellar Models
Describes the internal structure of a star in a detail and make predictions about the luminosity
Parsec
Distance at which one astronomical unit subtends an angle of one aresecond
Gravitational Lensing
Distribution of matter between a distant source and an observer that is capable of bending the light from the source
Inflation
Early in BB the expansion proceeded at a much more rapid rate than it did before or since
Rochelobes
Either of two lobes that form an hourglass shaped volume of space around a binary star system
Radiation
Emission of energy as electromagnetic waves
Local Group
Galaxy group that includes the milkyway. Mostly dwarf galaxies
Spiral Galaxy
Galaxy in which the stars and gas cloud are concentrated mainly in one or more spiral arms
Irregular galaxy
Galaxy that does not have a distinct shape
Flocculent
Having a loosely clumped texture
Open Universe
If there is not enough matter to exert a strong enough gravitational force to stop universal expansion, the universe is said to be open
Bok Globules
Isolated and relatively small dark nebulae, containing dust and gas from which star formation may take place
Globularclusters
Large compact spherical star cluster, typically of old stars in the outer regions of a galaxy
ISM (Interstellar Medium)
Matter that exists in the space between the star systems in a galaxy
Chandrasekhar Limit
Maximum mass of a stable white drawf star
Parallax
Measure distances to nearby stars
Absolute Magnitude
Measurement of a stars brightness from light years away
Central Bulge
Milky Way galaxy
Quintessence
Mysterious energy or force that has been postulated by atronomers that suggests the universe is expanding at an ever-increasing rate of speed
Magnetars
Neutron star with an extremely strong magnetic field
Dark Matter
Nonluminous material that is postulated to exist in space
X-ray Bursters
One class of x-ray binary stars exhibiting periodic and rapid increases in luminosity
Bipolar Flows
Opposite directed jets of gas are ejected by some protostellar objects
Proper Motion
Part of the apparent motion of a fixed star that is due to its actual movement in a space relative to the sun
Synchrotron Radiation
Polarized radiation emitted by a charged particle spinning in a magnetic field
Lagrange Points
Positions in an orbital configuration of two large bodies where a small object affected only by gravity can maintain a stable position relative to the two large bodies
CNO Cycle
Process of stellar nucleosynthesis in which stars on the main sequence fuse hydrogen into helium
Open Clusters
Relatively loose grouping of stars
Cosmology
Science of the origin &development of the universe
Closed Universe
Sufficient matter in the universe to halt the expansion driven by the big bang and cause eventual recollapse
Olber's Paradox
The argument that the darkness of the night sky conflicts with the assumption of an infinite and eternal static universe
Flat Universe
The dividing line between open and closed
Recombination
The early universe cooled enough for electrons and protons to bond together into hydrogen atoms
Look Back Time
The more distant an object being observed, the older the information recieved is
Gravitational Redshift
The process by which electromagnetic radiation originating from a source is reduced in frequency
Schwarzchild Radius
The radius of the boundary of a hole of this type
Big Bang
The rapid expansion of matter from a state of extremely high density and temperature
Hubble Law
The rate at which objects move away from eachother is proportional to their distance from eachother
Re-ionization
The reionization of hydrogen gas
Isotropic
The same in all directions
Homogeneous
The same in all locations
Cosmic Microwave Background Radiation
The thermal radiation that fills the universe and can be detected in every direction
Flux
The total amount of energy that crosses a unit area per unit time
Protostars
These are a large mass that forms by contraction of the gas of a giant molecular cloud in the interstellar medium
Hydrostatic Equilibrium
This occurs when external forces such as gravity are balanced by a pressure gradient force.
Neutron Star
Thought to form by the gravitational collapse of the remnant of a massive star after a supernova explosion
Convection
Transfer of heat by the circulation of the heated parts of a liquid or gas