chapter 19 Flashcards
- a gravitationally bound collection of stars, dust, gas & dark matter
- about 2 million in the observable universe
galaxy
spiral nebulae that were separated from the Milky Way
island universes
- spiral
- elliptical
- irregular
3 categories of galaxies
- a galaxy of Hubble type ‘E’ class with a circular to eccentric outline, containing almost no disk and a population of old stars
- subtypes ranging from nearly spherical (E0) to flat (E7)
elliptical galaxies
a galaxy of Hubble type ‘S’ class with a discernible disk in which large spiral patterns exist
spiral galaxies
the central region of a spiral galaxy that is similar in appearance to a small elliptical galaxy
bulge
a spiral galaxy with a bugle having an elongated, bar-like shape
barred spirals (SB)
the largest bulges and display tightly-wound and smooth spiral arms
Sa & SBa galaxies
small central bulges and more loosely wound spiral arms that appear more ‘knotty’ in appearance
Sc & SBc galaxies
a galaxy with a bulge and a disk-like spiral, but smooth in appearance like ellipticals
SO galaxies
- a galaxy without regular or symmetric appearance
- often lack symmetry in shape or structure
irregular galaxies
a small galaxy with a luminosity ranging from 1 million- 1 billion solar luminosities
dwarf galaxies
the amount of light emitted or reflected per unit area
surface brightness
- determine galaxy shapes
- in elliptical galaxies, stars move in random directions
- spiral galaxies have a flattened, rotating disk traveling in the same direction
stellar motions
- a sequence of techniques for measuring cosmic distances
- position provides a star’s luminosity, enabling astronomers to then estimate its distance by comparing its apparent brightness
distance ladder
- solar system - radar (10^-3 pc)
- nearby stars - parallax (1 pc)
- milky way - spectroscopic parallax (10^3 pc)
- nearby galaxies - cepheid variables (10^6 pc)
- distant galaxies - type 1a supernova (10^9 pc)
distance ladder sequence
- objects of a particular type, such as type 1a supernovae, that have a known luminosity
- astronomers combine the known luminosity & measured brightness of the object to find its distance
standard candle
- O stars
- globular clusters
- planetary nebulae
- novae
- cepheid variable stars
- supernovae
objects used as standard candles
a unit of distance equal to 1 million parsecs, or 3.26 million light-years
megaparsecs (pc)
- the empirical relationship between rotation velocity & luminosity
- for spiral galaxies
- half of the disk is blue-shifted, while the other half is red-shifted
-faster rotations make broader lines and require more mass to hold them together - more massive galaxies have more stars and more luminous
Tully-fisher relation
the speed at which a galaxy is moving away from Earth is proportional to the distance of that galaxy
hubble’s law
- H0
- the constant of proportionality relating the recession velocities of galaxies to their distances
hubble constant
matter in galaxies that emits light
luminous matter
particles of invisible matter that move slowly enough to be gravitationally bound even in the smallest galaxies
dark matter
- a plot showing how the orbital velocity of stars & gas in a galaxy changes with radial distances from the galaxy’s center
- astronomers measure the redshift & blueshift of individual stars and clumps of gas
rotation curve
the centrally condensed, greatly extended dark matter component of a galaxy that accounts for up to 95% of the galaxy’s mass
dark matter halo
- massive compact halo object that includes brown dwarfs, white dwarfs & black holes
- exert gravitational force & gravitational lensing
maCHOs
- weakly interactive massive particle
- considered an ‘elementary particle’
WIMPS
- quasi-stellar radio source
- the luminousity of the active galactic nuclei, seen only at great distances from the milky way
- shine with a luminosity of a trillion - thousand trillion suns
quasars
a highly luminous, compact galactic nucleus whose luminosity may exceed that of the rest of the galaxy
active galactic nucleus (AGN)
a type of spiral galaxy with an active galactic nucleus at its center and strong emission in the radio part of the spectrum
seyfert galaxies
a black hole of 1,00 solar masses or more that reside in the center of a galaxy and whose gravity powers active galactic nuclei
supermassive black holes
a 3-dimensional, donut-shaped ring
torus
accretion disk & a source of energy (gas & stars)
essential elements of AGN
