Astronomy Unit 7

Question 1

(or nuclear bulge) the central (round) part of the Milky Way or a similar galaxy

Answer 1

central bulge

Question 2

nonluminous mass, whose presence can be inferred only because of its gravitational influence on luminous matter; the composition of the dark matter is not known

Answer 2

dark matter

Question 3

the mass in the Milky Way that extends well beyond the boundary of the luminous stars to a
distance of at least 200,000 light-years from the center of the Galaxy; although we deduce its existence from its gravity, the composition of this matter remains a mystery

Answer 3

dark matter halo

Question 4

the idea that different parts of the Galaxy turn at different rates, since the parts
of the Galaxy follow Kepler’s third law: more distant objects take longer to complete one full orbit around the center of the Galaxy

Answer 4

differential galactic rotation

Question 5

the outermost extent of our Galaxy (or another galaxy), containing a sparse distribution of stars and globular clusters in a more or less spherical distribution

Answer 5

halo

Question 6

the band of light encircling the sky, which is due to the many stars and diffuse nebulae lying
near the plane of the Milky Way Galaxy

Answer 6

Milky way galaxy

Question 7

a star containing heavy elements; typically young and found in the disk

Answer 7

population I star

Question 8

a star with very low abundance of heavy elements; found throughout the Galaxy

Answer 8

population II star

Question 9

a spiral-shaped region, characterized by relatively dense interstellar material and young stars, that
is observed in the disks of spiral galaxies

Answer 9

spiral arm

Question 10

the object in the center of most large galaxies that is so massive and compact that light cannot escape from it; the Milky Way’s supermassive black hole contains 4.6 millions of Suns’ worth of mass

Answer 10

supermassive black hole

Question 11

a galaxy whose shape is an ellipse and that contains no conspicuous interstellar material

Answer 11

elliptical galaxy

Question 12

a constant of proportionality in the law relating the velocities of remote galaxies to their
distances

Answer 12

hubble constant

Question 13

a rule that the radial velocities of remove galaxies are proportional to their distances from us

Answer 13

Hubble’s law

Question 14

a galaxy without any clear symmetry or pattern; neither a spiral nor an elliptical galaxy

Answer 14

irregular galaxy

Question 15

the ratio of the total mass of a galaxy to its total luminosity, usually expressed in units of
solar mass and solar luminosity; the mass-to-light ratio gives a rough indication of the types of stars contained within a galaxy and whether or not substantial quantities of dark matter are present

Answer 15

mass-to-light ratio

Question 16

when lines in the spectra are displaced toward longer wavelengths (toward the red end of the visible spectrum)

Answer 16

redshift

Question 17

a flattened, rotating galaxy with pinwheel-like arms of interstellar material and young stars,
winding out from its central bulge

Answer 17

spiral galaxy