chapter 15

Question 1

• 90% hydrogen
• 10% helium

Answer 1

composition & density of the interstellar medium

Question 2

• small particles of grains of matter, particularly carbon and silicates, distributed throughout interstellar space
• effective at absorbing & diverting light

Answer 2

interstellar dust

Question 3

the dimming of visible and UV light by the interstellar dust

Answer 3

interstellar extinction

Question 4

removing blue light which causes an object to appear redder

Answer 4

reddening

Question 5

dust with a temp of 100K shines most strongly at a wavelength of 29nm, whereas cooler dust (10k) shines at a longer wavelength

Answer 5

wien’s law

Question 6

• warm
• high-density region of the interstellar medium made up mostly of atomic/molecular hydrogen & dust

Answer 6

interstellar clouds (2)

Question 7

• cool
• low-density region of the interstellar medium that fills the space between interstellar clouds

Answer 7

intercloud gas

Question 8

to strip the electron away from the atom, leaving only a positively charged nucleus

Answer 8

ionize

Question 9

less dense gas that composes 99% of the matter in the medium

Answer 9

interstellar gas

Question 10

a region of interstellar gas that has been ionized by UV radiation from nearby hot, massive stars

Answer 10

H II region

Question 11

• an interstellar cloud composed of mostly molecular hydrogen
• giant clouds have a mass of 100-1,000 of solar mass

Answer 11

molecular cloud (2)

Question 12

the gravitational attraction between all the parts of a cloud, which holds the cloud together and can sometimes make it collapse

Answer 12

self-gravity

Question 13

a dense clump within a molecular cloud that forms as the cloud collapses and fragments

Answer 13

molecular-cloud cores

Question 14

• protostar eventually switches from convection to radiation, which slows down the nuclear reactions
• infalling material adds to the mass & self-gravity of the protostar
• self-gravity is always matched by pressure
• star has to reach 10 million K in order to fuse hydrogen

Answer 14

evolving protostar (4)

Question 15

the path a star follows across the H-R diagram it evolves through its lifetime

Answer 15

evolutionary track

Question 16

• the path that a protostar follows on the H-R diagram as it contracts toward the main sequence
• explains the relationship between surface temp of a star and the temp deep in its interior

Answer 16

Hayashi track (2)

Question 17

an atom/molecule that lost or gained one or more electrons

Answer 17

ion

Question 18

material streaming away in opposite directions from both sides of the accretion disk of a young star

Answer 18

bipolar outflow

Question 19

a glowing, rapidly moving knot of gas & dust that is excited by bipolar outflows in young stars

Answer 19

herbig-haro objects

Question 20

a young stellar object that has dispersed enough of the material surrounding it to be seen in visible light

Answer 20

T Tauri stars

Question 21

• a group of stars that all formed at the same time in the same general location
• can take up to 10-100 million years to reach its main star sequence

Answer 21

star cluster (2)