Physics and the Universe 1080 Test 3

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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


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