Galaxy and Universe midterm #2

Question 1

zero-age main sequence

Answer 1

powered by fusion of H into He. all stars spend 90% of their lifetime on the main sequence

Question 2

Structural (hydrostatic) equilibrium

Answer 2

stars mass produces inward force of gravity which is balanced by the outward pressure of the gas in the interior of the star.

Question 3

Globular clusters and open (galactic) clusters

Answer 3

stars that are formed at the same time in the same place and from the same composition

Question 4

stellar evolution for different masses

Answer 4

lower mass stars evolve a lot slower than higher mass stars. Lower mass stars take billions of years to get off the main sequence where high mass stars only a couple hundred million to get off the main sequence

Question 5

The main sequence turn-off

Answer 5

the point on the main sequence where stars are just leaving the main sequence

Question 6

age of the cluster

Answer 6

the main sequence turnoff gives this

Question 7

low mass stellar evolution

Answer 7

after 5x10^9 years of hydrogen burning into helium there is a helium buildup and the He core collapses to a very small radius (earth) and a very high density

Question 8

electron degeneracy

Answer 8

dense core finds support from this holding it up by the electrons cannot be pushed any closer together

Question 9

interstellar dust

Answer 9

dark clouds silhouetted against a bright background. blocks light more blue than red

Question 10

interstellar extinction

Answer 10

where stars appear fainter

Question 11

interstellar redenning

Answer 11

stars appear redder

Question 12

Gas and dust

Answer 12

where the stars are originated

Question 13

interstellar clouds

Answer 13

dense region where dust and gas congregate

Question 14

ongoing star formation

Answer 14

H II regions that surround hot luminous o and b stars

Question 15

Neutral Hydrogen

Answer 15

H I, emits 21 cm radiation at radio wavelengths. used to map the Milky Way galaxy

Question 16

Molecular clouds

Answer 16

densest interstellar clouds temperature reaches as low as 10K

Question 17

Carbon Monoxide

Answer 17

used to map clouds

Question 18

Giant molecular clouds

Answer 18

largest clouds, prime region for star formation

Question 19

star formation

Answer 19

result in UV radiation from O and B stars that ionize their immediate surroundings

Question 20

cloud collapses

Answer 20

when their masses are great enough that self-gravity exceeds the outward pressure

Question 21

collapsing cores

Answer 21

forms separate stars

Question 22

protostars

Answer 22

the individual cores when collapse is underway

Question 23

clusters of stars

Answer 23

many protostars are formed at the same time and results in a cluster of stars

Question 24

Hydrogen fusion

Answer 24

begins when the protostar core becomes hotter until its temperature reaches around 10 million kelvin is when hydrogen fusion begins

Question 25

surface temperature of protostar

Answer 25

remains constant while collapse is slowly taking place and core is heating up. protostar is shrinking so its surface area is less and the luminosity is decreasing

Question 26

evolutionary track

Answer 26

the path a protostar or star takes on H-R diagram

Question 27

accretion disk

Answer 27

material falls onto protostar falls on this disk first then migrates inward

Question 28

bipolar outflow

Answer 28

protostar is blowing away 2 jets of material vertically perpendicular to the accretion disk

Question 29

Stellar wind from a protostar

Answer 29

eventually clears away the dust and gas cloud surrounding it and see it as a T Tauri star

Question 30

Evolutionary timescales of star formation

Answer 30

vary according to mass with the time to H burning being for: 100M - 10,000 years and 10M-100,000years and for 1M- 10,000,000years

Question 31

Hydrogen Shell burning

Answer 31

Hydrogen is still available in the shell surrounding the collapsed He core and provides the new energy source. luminosity increase and outer regions expand

Question 32

Helium core burning

Answer 32

He core gets more massive and shrinks more raising the temperature to 10^8K

Question 33

Helium flash

Answer 33

low mass stars, happens at same time throughout core in only a few minutes. The core temperature increases rapidly from 10^8 to 2x10^8. core expands explosively while the star as a whole shrinks

Question 34

Triple Alpha process

Answer 34

He^4+He^4>Be^8+He^4>C^12

Question 35

Horizontal branch or He burning main sequence

Answer 35

occurs after the Helium flash. now burning He in the core and H in the shell. sun will spend 100 million years on this branch

Question 36

Hydrogen and Helium shell burning

Answer 36

low mass stars never reach core temperatures high enough to burn carbon. When He is exhausted in the core it collapses again

Question 37

Second red giant branch

Answer 37

H and He burning in separate shells. as they go through this stage they lose large amounts of mass a total of 30-50% of its initial mass being lost

Question 38

white dwarf

Answer 38

The final result maximum mass of a white dwarf is 1.4. will eventually become a black dwarf

Question 39

nova

Answer 39

an explosion occurs and part of the outer layer of the star is blown away in 1000km/s.

Question 40

Type Ia supernovae

Answer 40

if the white dwarf exceeds the 1.4 mass limit collapse occurs and temperature rise to 6x10^8 to ignite C burning. ignites the entire star in 1 second and the star is completely destroyed

Question 41

Type Ia supernova

Answer 41

large fraction of the star is converted into radioactive iron (Fe) and nickel (Ni) and blasted into space. a luminosity of 10^10 times the sun and outshines the entire galaxy for a time

Question 42

high mass stellar evolution

Answer 42

stars greater than 8M higher temperatures in the core make additional nuclear reactions possible

Question 43

CNO cycle

Answer 43

when He burning begins massive star does not go up the red giant branch. moves horizontally across the H-R diagram to the right

Question 44

final stage of high mass star

Answer 44

no support for iron core so it collapses electron degeneracy occurs but not strong enough to support core. collapse continues.

Question 45

What does the temperature get to on the final stage of a high mass star

Answer 45

10^10K

Question 46

What do Gamma rays do in the final stage of high mass stars

Answer 46

break apart Fe nuclei into He nuclei. Electrons are forced into nuclei combine with protons to form neutrons

Question 47

type II supernova

Answer 47

collapse is very fast. density of core exceeds the density of an atomic nucleus core bounces back and shock wave moves outward. neutrinos are absorbed (about0.2%)