Astronomy Unit 9

Question 1

slow-moving massive particles, not yet identified, that don’t absorb, emit, or reflect light or
other electromagnetic radiation

Answer 1

cold dark matter

Question 2

the assumption that, on the large scale, the universe at any given time is the same
everywhere—isotropic and homogeneous

Answer 2

cosmological principle

Question 3

an energy that is causing the expansion of the universe to accelerate; the source of this energy is
not yet understood

Answer 3

dark energy

Question 4

changes in individual galaxies over cosmic time, inferred by observing snapshots of
many different galaxies at different times in their lives

Answer 4

evolution (of galaxies)

Question 5

a process by which a larger galaxy strips material from or completely swallows a smaller
one

Answer 5

galactic cannibalism

Question 6

having a consistent and even distribution of matter that is the same everywhere

Answer 6

homogeneous

Question 7

massive particles, not yet identified, that don’t absorb, emit, or reflect light or other
electromagnetic radiation; hot dark matter is faster-moving material than cold dark matter

Answer 7

hot dark matter

Question 8

the same in all directions

Answer 8

isotropic

Question 9

a small cluster of galaxies to which our Galaxy belongs

Answer 9

local group

Question 10

a collision between galaxies (of roughly comparable size) that combine to form a single new structure

Answer 10

merger

Question 11

a galaxy or merger of multiple galaxies that turns gas into stars much faster than usual

Answer 11

starburst

Question 12

a large region of space (more than 100 million light-years across) where groups and clusters of
galaxies are more concentrated; a cluster of clusters of galaxies

Answer 12

supercluster

Question 13

a region between clusters and superclusters of galaxies that appears relatively empty of galaxies

Answer 13

void