chapter 19

Question 1

• a gravitationally bound collection of stars, dust, gas & dark matter
• about 2 million in the observable universe

Answer 1

galaxy

Question 2

spiral nebulae that were separated from the Milky Way

Answer 2

island universes

Question 3

• spiral
• elliptical
• irregular

Answer 3

3 categories of galaxies

Question 4

• 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)

Answer 4

elliptical galaxies

Question 5

a galaxy of Hubble type ‘S’ class with a discernible disk in which large spiral patterns exist

Answer 5

spiral galaxies

Question 6

the central region of a spiral galaxy that is similar in appearance to a small elliptical galaxy

Answer 6

bulge

Question 7

a spiral galaxy with a bugle having an elongated, bar-like shape

Answer 7

barred spirals (SB)

Question 8

the largest bulges and display tightly-wound and smooth spiral arms

Answer 8

Sa & SBa galaxies

Question 9

small central bulges and more loosely wound spiral arms that appear more ‘knotty’ in appearance

Answer 9

Sc & SBc galaxies

Question 10

a galaxy with a bulge and a disk-like spiral, but smooth in appearance like ellipticals

Answer 10

SO galaxies

Question 11

• a galaxy without regular or symmetric appearance
• often lack symmetry in shape or structure

Answer 11

irregular galaxies

Question 12

a small galaxy with a luminosity ranging from 1 million- 1 billion solar luminosities

Answer 12

dwarf galaxies

Question 13

the amount of light emitted or reflected per unit area

Answer 13

surface brightness

Question 14

• determine galaxy shapes
• in elliptical galaxies, stars move in random directions
• spiral galaxies have a flattened, rotating disk traveling in the same direction

Answer 14

stellar motions

Question 15

• 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

Answer 15

distance ladder

Question 16

1. solar system - radar (10^-3 pc)
2. nearby stars - parallax (1 pc)
3. milky way - spectroscopic parallax (10^3 pc)
4. nearby galaxies - cepheid variables (10^6 pc)
5. distant galaxies - type 1a supernova (10^9 pc)

Answer 16

distance ladder sequence

Question 17

• 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

Answer 17

standard candle

Question 18

• O stars
• globular clusters
• planetary nebulae
• novae
• cepheid variable stars
• supernovae

Answer 18

objects used as standard candles

Question 19

a unit of distance equal to 1 million parsecs, or 3.26 million light-years

Answer 19

megaparsecs (pc)

Question 20

• 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

Answer 20

Tully-fisher relation

Question 21

the speed at which a galaxy is moving away from Earth is proportional to the distance of that galaxy

Answer 21

hubble’s law

Question 22

• H0
• the constant of proportionality relating the recession velocities of galaxies to their distances

Answer 22

hubble constant

Question 23

matter in galaxies that emits light

Answer 23

luminous matter

Question 24

particles of invisible matter that move slowly enough to be gravitationally bound even in the smallest galaxies

Answer 24

dark matter

Question 25

- 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

Answer 25

rotation curve

Question 26

the centrally condensed, greatly extended dark matter component of a galaxy that accounts for up to 95% of the galaxy's mass

Answer 26

dark matter halo

Question 27

- massive compact halo object that includes brown dwarfs, white dwarfs & black holes - exert gravitational force & gravitational lensing

Answer 27

maCHOs

Question 28

- weakly interactive massive particle - considered an 'elementary particle'

Answer 28

WIMPS

Question 29

- 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

Answer 29

quasars

Question 30

a highly luminous, compact galactic nucleus whose luminosity may exceed that of the rest of the galaxy

Answer 30

active galactic nucleus (AGN)

Question 31

a type of spiral galaxy with an active galactic nucleus at its center and strong emission in the radio part of the spectrum

Answer 31

seyfert galaxies

Question 32

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

Answer 32

supermassive black holes

Question 33

a 3-dimensional, donut-shaped ring

Answer 33

torus

Question 34

accretion disk & a source of energy (gas & stars)

Answer 34

essential elements of AGN