Homework #4

Due: August 4

Physics 5

1) How close is the nearest star to the Sun?

a) 1.3 parsecs

b) 270 AU

c) 3.1 x 106 m

d) 1220 light-years

2) Star A has a parallax of 0.2”. Star B has a parallax of 0.1”. Which star is more distant from Earth?

a) A

b) B

c) They are the same distance

d) Need more information

3) What would you use to calculate a star’s true space motion?

a) Transverse motion and proper motion

b) Radial velocity and parallax

c) Radial velocity and transverse motion

d) True space motion is directly measurable

4) How do we find the radius of most stars?

a) Measure it directly using speckle interferometry

b) Measure its gravitational effect on other stars

c) Find its parallax

d) Calculate it by finding its temperature and luminosity

5) What kind of star is the Sun?

a) Giant

b) Supergiant

c) Dwarf

d) Neutron star

6) Star A and Star B have the same luminosity. If Star A is 4 times as distant as Star B, then:

a) Star A is 4 times as bright as Star B

b) Star B is 4 times as bright as Star A

c) Star A is 16 times as bright as Star B

d) Star B is 16 times as bright as Star A

7) Why do we match a star’s black body curve to a known black body curve?

a) To find the temperature

b) To find the mass

c) To find the magnitude

d) To find the radius

8) Which of the following is true?

a) An O type star is cooler than a G type star

b) A K type star is hotter than an A type star

c) A G type star is cooler than a B type star

d) An F type star is cooler than an M type star

9) H-R diagrams are graphs of:

a) Distance vs brightness

b) Temperature vs luminosity

c) Spectral type vs mass

d) Radius vs proper motion

10) The main sequence is:

a) The part of the H-R diagram where most stars live

b) The line on the H-R diagram representing stars of the same mass

c) The path that a star takes on the H-R diagram during its lifetime

d) The line on the H-R diagram that divides dwarf stars from giant stars

11) What type of star is thought to comprise most of the stars in the universe?

a) Red dwarf

b) Red giant

c) Blue giant

d) White dwarf

12) A star which lies in the lower left region of the H-R diagram will have what properties?

a) Large, hot, bright

b) Small, cold, bright

c) Small, hot, dim

d) Small, cold, dim

13) Using an H-R diagram, a bright K-type star would most likely be:

a) Red dwarf

b) White dwarf

c) Red giant

d) On the main sequence

14) Which of the following stellar qualities is NOT directly related to the others?

a) Color

b) Luminosity

c) Temperature

d) Spectral type

15) Luminosity class can be determined by measuring:

a) Parallax

b) Spectral line width

c) Proper motion

d) Brightness

16) You identify spectroscopic binaries by:

a) Looking at the star’s position on the H-R diagram

b) Resolving two stars on the sky and observing the orbit by proper motion

c) Finding a periodic dip in the light curve

d) Measuring the periodic change in Doppler shift

17) The stellar property which determines all other properties of the star, and thus its position on the main sequence, is:

a) Mass

b) Age

c) Luminosity

d) Angular momentum

18) Which of these stars will live the longest?

a) The Sun (G-type)

b) Blue giant

c) Red dwarf

d) No way to tell

19) Which of the following statements about an open cluster and a globular cluster is likely to be true?

a) The open cluster has many more stars

b) The globular cluster has more high-mass stars

c) The open cluster has more red giant stars

d) The globular cluster is older

20) Why are clusters useful for making an H-R diagram?

a) Since all the stars are the same distance from Earth, their absolute and apparent luminosities are related the same way

b) Since all the stars have the same mass, their other properties will all be nearly identical

c) Since all the stars are of the same composition, they will all be located at the same place on the main sequence

d) Since all the stars are the same age, they will all have the same temperature

21) Which of the following statements about the interstellar medium is true?

a) It consists mainly of dust

b) It is about the same density as Earth’s atmosphere

c) It tends to block higher-frequency light from stars

d) It is made mostly of helium

22) Which of these is NOT a reason that 21cm radiation is a good tool for observing hydrogen?

a) The 21cm wavelength is greater than the size of interstellar dust particles, so the dust doesn’t block the light

b) Because it is low energy, it is very easy and common for hydrogen to emit

c) It is a good probe of atomic hydrogen, which comprises the majority of all matter in the universe

d) 21cm is an especially easy wavelength to observe, since almost all telescopes can observe it

23) What are the largest objects in interstellar space?

a) Molecular clouds

b) Atomic hydrogen clouds

c) Emission nebulae

d) Dust lanes

24) The dark patches across the sky are:

a) Places where there is no material

b) Places where dark matter dominates

c) Places where dust lanes block the light

d) Places where stars have not yet formed, so they are not bright yet

25) What is the largest constituent of molecular clouds?

a) H2

b) H2O

c) NH3

d) CO

26) How do most stars form?

a) Hydrogen clouds heat up enough from outside light that nuclear fusion can begin

b) Large interstellar clouds collapse under their own gravity and break up

c) Small clouds of interstellar gas collide and stick together until enough mass accumulates to make a star

d) Magic

27) What are brown dwarfs?

a) The hottest stars known

b) Objects not massive enough to have nuclear fusion

c) Remnants of low-mass stars which have completed their life cycles

d) A protostar which is warm enough to emit infrared light, but not yet hot enough for hydrogen burning

28) What causes stars like the Sun to grow into red giants at the end of their lives?

a) The star accretes material from its binary companion and grows to a giant

b) The hydrogen is mostly burned away by then, so there is less gravity pulling in on the star

c) Excess helium builds up from nuclear fusion in the core and pushes outward

d) Hydrogen burning in a shell around the core creates extra pressure, which overcomes gravity

29) What is a planetary nebula?

a) Cloud of gas which will eventually collapse to form planets

b) Disk of matter which is accreted in a binary system

c) Flash emitted by a white dwarf during a nova

d) Expelled outer envelope of a star, ejected when helium fusion stops

30) During what stage of stellar evolution will a star spend about 95% of its lifetime?

a) Main sequence

b) T Tauri

c) Horizontal branch

d) Red giant

31) What is the heaviest element that stars can produce by nuclear fusion?

a) Iron

b) Silicon

c) Oxygen

d) Lead

32) A binary system consists of a main sequence star and a white dwarf. After accreting hydrogen and burning it off many times, the white dwarf accumulates enough matter to burn carbon. Immediately carbon burning ignites in the white dwarf, and it explodes violently. What has just occurred?

a) Nova

b) Type I supernova

c) Type II supernova

d) Helium flash

33) Which type of star will have the shortest lifetime?

a) Low mass

b) High mass

c) Low temperature

d) Small radius

34) Which of the following is NOT a possible remnant from a Type II supernova?

a) Millisecond pulsar

b) White dwarf

c) X-ray burster

d) Black hole

35) How are the heaviest elements (uranium, gold, etc.) formed?

a) Supernovae explosions

b) Fusion in neutron stars

c) Ejection of planetary nebulae

d) Plate tectonics in Earth’s crust

36) By examining the main-sequence turnoff of a cluster, we can infer the cluster’s:

a) Distance

b) Mass

c) Age

d) Temperature

37) What is the Schwarzschild radius?

a) The radius at which stars with a larger radius will collapse to a singularity

b) The radius at which nothing can escape the gravitational pull of an object

c) The radius at which matter orbiting a star will accrete onto the star

d) The radius at which the gravitational pull of the stars in a binary system is equal

38) Which of the following statements about neutron stars is true?

a) They form after a nova

b) Only a small fraction of young neutron stars spin rapidly

c) Neutron stars are strongly magnetized when the form

d) When a neutron star gets old, it begins to emit beams of radiation

39) Black holes:

a) Form when a neutron star slows its spin rate, and the centripetal force can no longer balance gravity

b) Suck in everything near them, so there is no way to ever detect its presence

c) Are by far the most massive objects in the known universe

d) Have an event horizon, within which nothing can escape

40) General relativity tells us that:

a) Black holes will blueshift light emitted near the event horizon

b) Clocks near a black hole will speed up (time dilation)

c) The core of a supermassive star will collapse to a single point (singularity)

d) The speed of light is the same in all reference frames