ASTR1110H – FIRST MIDTERM



NAME________________________________________________________________________________________

ASTR 1020 – FINAL EXAM

Friday, December 9, 2011

Professor Loris Magnani

There are 34 questions on this exam. 30 are multiple-choice and 4 are written problems. Write your answer right on this exam; for the multiple choice by circling one of the 5 choices or writing the letter corresponding to your choice next to the question. For the written problems, please show your work if you wish for any partial credit. If you circle more than one multiple-choice answer, make sure you make clear to me which answer is your actual choice, because if I have any doubts, I will just mark the question as being wrong. Each multiple-choice question that is correct is worth 2 points for a total of 60 points. Each written problem is worth 10 points, so the maximum score you can get on the exam is 100. There is only one best answer to each multiple-choice question. There is a sheet at the end of this exam with formulas and constants that you may need. You may use a calculator. GOOD LUCK!

1. Edwin Hubble discovered that nearly all galaxies are moving away from us with a speed that depends directly on their distance. What is the best interpretation of this observational fact?

a) The Universe has neither a beginning nor an end.

b) The Universe is expanding.

c) The Universe is contracting.

d) Galaxies do not obey the Doppler-shift relation.

e) Quantum Mechanics does not work on galactic scales.

2. Which of the following is NOT a prediction of the Big Bang Theory?

a) The baryonic content of the Universe should be about three-quarters hydrogen and one-quarter helium.

b) The early Universe was very hot.

c) Galaxies should show redshifts.

d) A Cosmic Background Radiation should exist.

e) The early Universe was very cold.

3. The Hubble Law lets you obtain a galaxy’s distance if you know its

a) velocity

b) mass

c) linear size

d) angular size

e) all of the above

4. What can be learned by calculating the value of 1/Ho?

a) the approximate age of the Universe

b) the approximate mass of the Universe

c) the recessional velocity of galaxies

d) the redshift of any galaxy

e) the amount of baryons in the Universe

5. What is the Cosmic Background Radiation (CBR)?

a) the ionized plasma from the early Universe

b) the photons from receding galaxies

c) the photons from the early Universe

d) the photons from active galactic nuclei (AGNs)

e) the decaying baryons from the early Universe

6. If I double the mass of the Earth, what happens to your weight?

a) Nothing; it does not change.

b) It doubles.

c) It is halved

d) It becomes larger by a factor of 4.

e) It becomes smaller by a factor of 4.

7. Which of the following is the best description for light?

a) Light is composed only of energetic particles.

b) Light is composed only of energetic waves.

c) Light is composed of thermal radiation.

d) Light is a sequence of varying electric and magnetic fields.

e) Light is a sequence of high-speed electrons.

8. If you take a spectrum along path A in the diagram below, what type of spectrum do you expect to see?

a) continuous spectrum

b) thermal or blackbody spectru

c) absorption line spectrum

d) emission line spectrum

e) synchrotron emission spectrum

9. If you double the frequency of a beam of ultraviolet light, what happens to its wavelength?

a) it stays the same

b) it doubles

c) it is halved

d) it increases by a factor of 4

e) it decreases by a factor of 4

10. A beam of light has a wavelength of 4.6 x 10-7 m and a frequency of 6.5 x 1014 Hz. What is the speed of the photons?

a) 7.1 x 108 m/s

b) 1.4 x 107 m/s

c) 5.5 x 107 m/s

d) 3.0 x 108 m/s

e) 1.4 x 108 m/s

11. Which type of galaxy is composed primarily of old stars with some hot gas throughout its interior?

a) irregular galaxy

b) spiral galaxy

c) barred spiral galaxy

d) AGN

e) elliptical galaxy

12. The most mass in a spiral galaxy is in the form of

a) hydrogen

b) helium

c) dark matter

d) dark energy

e) dust

13. What can you find at the center of an AGN?

a) star cluster

b) supermassive black hole

c) dark matter bulge

d) stellar bulge

e) supermassive black hole with an accretion disk

14. The rotation curves of spiral galaxies are odd because they

a) remain flat at large distances from the center

b) drop to 0 at large distances from the center

c) drop off in Keplerian fashion

d) increase linearly at large distances from the center

e) become sinusoidal at large distances from the center

15. How does dark matter differ from normal matter?

a) Dark matter does not have a gravitational interaction.

b) Dark matter does not have an electromagnetic interaction.

c) Dark matter produces a degenerate pressure.

d) Dark matter interacts strongly with photons.

e) All of the above.

16. Given the spectral sequence O, B, A, F, G, K, M, which type of star has the largest size?

a) O

b) F

c) K

d) M

e) There is not enough information to answer this question.

17. What is true for all stars on the Main Sequence?

a) They all have the same temperature.

b) They all have the same radius.

c) They all have the same luminosity.

d) They all have the same pressure.

e) They all convert hydrogen to helium in their cores.

18. Imagine that 2 stars, one called A and one called B, have the same luminosity. Star A is larger than Star B. What can you say about their surface temperatures?

a) Star A has a higher surface temperature than B.

b) Their surface temperatures are the same.

c) Star B has a higher surface temperature than A.

d) Star A has a higher surface temperature for the first 100 million years, but afterwards, Star B has the higher surface temperature.

e) There is not enough information to answer this question.

19. A star has a parallax angle of 0.0034 arcseconds. How far away is it?

a) 3.4 pc

b) 29.4 pc

c) 34.2 pc

d) 294 pc

e) 342 pc

20. In an HR diagram which of the following quantities can be plotted on the x-axis of the diagram?

a) spectral type and temperature

b) temperature and radius

c) radius and luminosity

d) luminosity and spectral temperature

e) luminosity and temperature

21. Mass and energy are equivalent according to Einstein’s Theory of Special Relativity. What form of mass or energy dominates the Universe?

a) Dark Energy

b) Dark Matter

c) Hydrogen

d) Baryons

e) Neutrinos

22. What theory is invoked to explain the Flatness Problem and the Horizon Problem in the Big Bang Theory?

a) Neutrino Oscillation

b) Dark Energy

c) Dark Matter

d) Cosmic Background Radiation

e) Inflation

23. By studying Type I Supernovae, astronomers have determined that the Universe is

a) stationary

b) contracting

c) accelerating

d) decelerating

e) dominated by baryons

24. How old is the Universe?

a) 35.4 million years

b) 13.7 billion years

c) 4.6 billion years

d) 29.3 billion years

e) 2.3 billion years

25. The most recent measurements from the WMAP team indicate that the topology or basic shape of the Universe is

a) flat

b) spherical

c) hyperbolic

d) parabolic

e) degenerate

26. Protostars that form from molecular cloud cores and have masses less than 0.08 solar masses become

a) white dwarfs

b) red giants

c) main sequence stars

d) neutron stars

e) brown dwarfs

27. A white dwarf is supported against collapse by electron degenerate pressure. This pressure can support at most how much mass before collapse is inevitable?

a) 0.08 solar masses

b) 0.55 solar masses

c) 1.44 solar masses

d) 8 solar masses

e) 50 solar masses

28. When a main sequence star begins to run out of nuclear fuel at the core, why does it become more luminous?

a) The shrinking hydrogen core ignites.

b) The radiation from the core becomes degenerate.

c) The rate of hydrogen burning at the surface of the star increases.

d) The helium core begins to expand.

e) The shrinking helium core causes the hydrogen burning shell to burn at at higher temperature.

29. Stars of 8 solar masses or less return some of their mass to the interstellar medium via

a) planetary nebulae

b) supernova remnants

c) degenerate matter

d) accretion disk

e) pulsar jets

30. If a red giant star in a binary system with a white dwarf dumps enough gas onto the surface of the white dwarf to drive it over the Chandrasekhar limit, what then happens?

a) Nothing. The red giant just loses some mass.

b) The white dwarf becomes a red-giant.

c) The white dwarf blows up in a Type II supernova.

d) The white dwarf blows up in a Type I supernova.

e) The white dwarf blows up in a planetary nebula.

Problems. (10 points each)

31. The rest wavelength of a spectral line that we are interested in is at 632.5 nanometers (1 nanometer = 1 x 10-9 meters)? We observe this line from a galaxy and find that its wavelength is at 788.2 nanometers.

a) What is the redshift (z) of this galaxy ?

b) What is its recessional velocity in km/s ?

c) What is its distance in megalight-years or megaparsecs ?

32. Imagine that a star converts 8.5 x 1010 kg of H into Helium every second. What is the star’s luminosity?

33. Imagine that an object has a mass of 1.3 solar masses. If it has a radius of 1 x 104 km, what is its density in kg/m3 ? What type of object is it?

34. Imagine that a brown dwarf of 0.02 solar masses is orbiting a main sequece star star of 40 solar masses at a distance of 1 x 1015 m. What is the period of rotation of the brown dwarf?

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