Astronomy Chapter 24 Vocab- "Galaxies"

spiral galaxies

galaxies that are classified according to the size of their central bulge; from largest to smallest, the three types include Sa, Sb, and Sc

elliptical galaxies

galaxies that have no spiral arms and no galactic disk; they come in many sizes, contain little to no cool gas and dust, and are classified according to their shape from E0 (almost spherical) to E7 (most elongated)

lenticular galaxies

galaxies that have a disk and bulge, but no spiral arms or interstellar gas; are classified as S0 and SB0 galaxies

irregular galaxies

galaxies that have a wide variety of shapes; examples are the small and large Magellanic clouds

Hubble’s “tuning fork”

a convenient way to remember the galaxy classifications, although it has no deeper meaning

Tully-Fisher relation

a process that correlates a galaxy’s rotation speed (which can be measured using the Doppler effect) to its luminosity

“standard candles”

objects whose absolute magnitude is known, and which can therefore be used to determine distance using their apparent magnitude

Local Group

a galaxy cluster that contains 3 spirals: the Milky Way, the Andromeda Galaxy, and M33

galaxy cluster

a group of galaxies held together by its own gravity

Hubble’s Law

used to measure the distance of galaxies; states that the further away the galaxy is from us, the faster it appears to be moving away from us, and distance and recessional velocity have a direct relationship

Universal Recession

states that all galaxies (with a couple of nearby exceptions) seem to be moving away from us, with the redshift of their motion correlated with their distance

Hubble galaxies

galaxies that are far too luminous to be part of the Hubble scheme

nonstellar radiation

radiation that emits from Hubble galaxies

Seyfert galaxies

active galaxies that resemble normal spiral galaxies, but have cores that are thousands of times more luminous

radio galaxies

active galaxies that have enormous lobes, invisible to optical telescopes and perpendicular to the plane of the galaxy

quasar galaxies

active galaxies that are starlike in appearance, but are not stars at all and have unusual spectral lines

Properties of Active Galactic Nuclei

have high luminosity, nonstellar energy emission, variable energy output, jets and other signs of explosive activity, and broad emission lines