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47 terms

Astronomy 1300 Test #4

matter consisting of antiparticles such as antiprotons, antineutrons, and positrons
flatness problem
the dilemma posed by the fact that the combined average mass density of the universe is very nearly equal to the critical density
grand unified theory
a theory that describes and explains the four physical forces
a sudden expansion of space
isotropy problem
the dilemma posed by the fact that the cosmic microwave background is isotropic; also called the horizon problem
the process of building up nuclei such as deuterium and helium from protons and neutrons
pair production
the creation of a particle and its antiparticle from energy
population III star
one of the first stars to form after the big bang, composed of only hydrogen, helium and tiny amounts of lithium and beryllium; a "zeroth-generation" star
big bang
an expansion of all space that took roughly 13.7 billion years ago that marks the beginning of the universe
closed universe
a universe with positive curvature, so that its geometry is analogous to that of the surface of a sphere
cosmic microwave background
an isotropic radiation field with a blackbody temperature of about 2.725 K that permeates the entire universe
cosmological principle
the assumption that the universe is homogeneous and isotropic on the largest scale
cosmological redshift
a redshift that is caused by the expansion of the universe
dark energy
a form of energy that appears to pervade the universe and causes the expansion of the universe to accelerate but has no discernible gravitational effect
flat universe
space that is not curved; space with zero curvature
observable universe
the portion of the universe inside our cosmic light horizon
olber's paradox
the dilemma associated with the fact that the night sky is dark
open universe
a universe with negative curvature, so that its geometry is analogous to a saddle-shaped hyperbolic (saddle) surface
active galactic nucleus
the center of an active galaxy
active galaxy
a galaxy that is emitting exceptionally large amounts of energy: a seyfert, radio galaxy, or quasar
a type of active galaxy whose nucleus has a featureless spectrum
double radio source
an extragalactic radio source charecterized by two large regions of radio emission, typically located on either side of an active galaxy
a very luminous object with a very large redshift and a star-like appearance
radio galaxy
a galaxy that emits an unusually large amount of radio waves
radio lobes
a region near an active galaxy from which significant radio radiation is emitted
seyfert galaxy
a spiral galaxy with a bright nucleus whose spectrum exhibits emission lines
barred spiral galaxy
a spiral galxy in which the spiral arms begin from the ends of a bar running through the nucleus rather than from the nucleus itself
clusters of galaxies
a collection of galaxies containing a few to several thousand member galaxies
distance ladder
the sequence of techniques used to determine the distances to very distant galaxies
elliptical galaxy
a galaxy with an elliptical shape and no conspicuous interstellar material
gravitational lens
a massive object that reflects light rays from a remote source, forming an image much as an ordinary lens does
hubble flow
the recessional motion of distant galaxies caused by the expansion of the universe
hubble law
the empirical relationship stating that the redshifts of remote galaxies are directly proportional to their distances from earth
irregular galaxy
an asymmetrical galaxy having neither spiral arms nor an elliptical shape
lenticular galaxy
a galaxy with a central bulge and a disk but no spiral structure; an SO galaxy
local group
a cluster of about 40 galaxies of which the milky way is a member
spiral galaxy
a flattened rotating galaxy with pinwheel like spiral arms winding outward from the galaxys nucleus
central bulge
a spherical distribution of stars around the nucleus of a spiral galaxy
dark matter
nonluminous matter that is the dominant form of matter in galaxies and throughout the universe
density wave
in a spiral galaxy, a localized region in which matter piles up as it orbits the center of the galaxy
disk of a galaxy
the disk-shaped distribution of population I stars that dominates the appearance of a spiral galaxy
a spherical distribution of globular clusters and population II stars that surround a spiral galaxy
Massive compact halo object (MACHO)
a dim star or low-mass black hole that may comprise part of the unseen dark matter
rotation curve
a plot of the orbital speeds of stars and nebulae in a galaxy versus distance from the center of the galaxy
self-propagating star formation
the process by which the formation of stars in one location in a galaxy stimulates the formation of stars in a neighboring location
spiral arm
lanes of interstellar gas, dust and young stars that wind outward in a plane from the central region of a galaxy
weakly interacting massive particle (WIMP)
a hypothetical massive particle that may comprise part of the unseen dark matter