Describe the gravitational lensing technique

Question

Assignment:

Question 1. Which best describes the "gravitational lensing" technique for finding exoplanets?

• a massive object magnifies and distorts the light from an object behind it
• the wavelengths of light from a star are shifted as it moves about its center of mass
• a planet passes in front of its parent star and blocks part of its light
• a massive object accelerates another object that passes close to it

Question 2. Direct imaging generally can only detect what kind of exoplanets:

• small and at great distances from their parent star
• very large and at great distances from their parent star
• very large and close to their parent star
• small and close to their parent star

Question 3. The RV (radial velocity) involved creating a graph of the star's radial velocity vs what other parameter?

• radial velocity against time
• radial velocity against luminosity
• radial velocity against brightness
• radial velocity against distance

Question 4. When star moves away from us, the wavelengths of the starlight:

• are the same as if the star were not moving
• are shorter than if the star were not moving
• can be longer or shorter depending on the distance to the star
• are longer than if the star were not moving

Question 5. Identify the method that is generally used to determine the diameter of an exoplanet?

• detection of brightness changes in a star as a planet passes in front of it
• detection of reflected starlight
• detection of Doppler shifts in the spectra of the parent stars
• regular changes in the positions of the parent stars with respect to more distant stars as they move across the sky

Question 6. Most exoplanets have been discovered using which method?

• detection of brightness changes in a star as a planet passes in front of it
• detection of Doppler shifts in the spectra of the parent stars
• detection of reflected starlight
• regular changes in the positions of the parent stars with respect to more distant stars as they move across the sky

Question 7. How do planet formation scientists explain so many Jupiter-mass planets found within 1 astronomical unit of their host star?

• the Jovian planets formed farther out and then migrated inward
• these are massive terrestrial planets that formed close to their parent stars
• they are brown dwarfs that were captured by their parent stars
• they are Jovian planets that were spun out from their rapidly spinning parent stars

Question 8. Transits of an exoplanet across the stellar surface requires what condition:

• planet has to be very large
• parent star has to be very small
• orbital plane of the planet has to be aligned along our line of sight
• orbital plane has to be perpendicular to our line of sight

Question 9. Astronomers find a planet a few time more massive than Earth and with an average density similar to rock. What do they call such an exoplanet?

• super-Jovian
• mini-Neptune
• super-Earth
• mega-Earth

Question 10. The center of mass of Sun and Jupiter lies where:

• just outside the orbit of Mercury
• exactly at the center of the Sun
• midway between the Sun and Jupiter
• inside the volume of the Sun

Question 11. An exoplanet is known to have a mass 2000x lower than its host star. If the host star is measured to move around its center of mass every 10 years, what is the orbital period of the PLANET?

• this cannot be determined from this observation
• 200000 years
• 20 years
• 10 years
• 1.8 days

Question 12. Based on what we know about how stars age with time, which is most true?

• the more heavy elements it contains
• the faster it evolves
• the slower it evolves
• the more planets it has around it

Question 13. Approximately how many confirmed exoplanets have been discovered ?

• 4000
• 100 billion
• 1000
• 100

Question 14. The Doppler shift method has most difficulty detecting which kind of exoplanets?

• a massive planet far from its parent star
• a low mass planet far from its parent star
• a low mass planet close to its parent star
• a massive planet close to its parent star

Question 15. When was first exoplanet found around a Sun-like star?

• 1990
• 2000
• 2005
• 1995

Question 16. in 1974, Drake and Sagan sent a message to M13, a globular cluster about 20000 light-years away. When is the soonest we could receive a response from aliens there?

• 20,000 years
• 80,000 years
• 40,000 years
• 10,00 years

Question 17. What was the main reason the US Government spend resources to investigate UFOs after World War II?

• were themselves developing new types of aircraft and used the official investigation as a cover-up
• were afraid that an alien civilization was in the process of invading the Earth
• thought that they might be new types of aircraft being developed by the Soviet Union
• knew that UFOs were alien craft and used the official investigation as a cover-up

Question 18. Why are scientists pessimistic about detecting signals from civilization in other galaxies?

• signals from civilizations on other galaxies will not reach us before we give up listening
• other galaxies are unlikely to harbor intelligent civilizations
• signals from other galaxies will be severely weakened by distance, making them far harder for us to detect
• they will most likely transmit at wavelengths that will be absorbed by intergalactic gas

Question 19. Which is the best answer for how far we have searched for signs of alien radio signals used modern SETI? This includes signals stronger than just TV/radio leakage.

• <10 light-years
• >1000 light-years
• the whole galaxy
• few hundred light-years

Question 20. Suppose that there are 1 billion (1,000,000,000,000) habitable planets in a nearby galaxy, that 1 in 5 habitable planets has life, that 1 in 1000 planets with life has at some point had an intelligent civilization, and that 1 in 1000 civilizations that have ever existed is in existence now. How many civilizations would exist at present?

• 2
• 200
• 20
• 2,000

Question 21. In past studies, roughly 90% of UFO sightings

• are hoaxes
• can be explained by natural phenomena
• are real sightings of alien craft
• cannot be explained

Question 22. Which statement best describes our confidence in results derived from the Drake Equation?

• it is impossible for us to ever know the values of any of the factors
• we have decent estimates for the first three factors, but not the last factors
• we do not have good knowledge for any of the factors in the equation
• we have an exact number for the first factor, but not for any of the other factors

Question 23. We can crudely estimate the intelligence of extinct species using the Encephalization Quotient (EQ). How is the EQ for extinct species estimated?

• extinct species always have the same EQ value
• there is a linear relationship between the EQ and time, thus allowing extrapolation
• we can estimate their body masses from their fossilized remains and their brain masses from the sizes of their fossilized cranial cavities
• we can always find similar species in existence today to make measurements of

Question 24. Optical lasers have been suggested as a means of alien communication.. What is one advantage of using lasers over radio ?

• optical lasers can penetrate through dust better than radio waves
• lasers can be focused into a tighter beam,wasting less energy during communication than radio waves.
• lasers are easier to make than radio waves
• There is nothing better about visible lasers compared to radio waves for communication
• optical light is the only wavelength that can penetrate our atmosphere

Question 25. Which kind of extraterrestrial signal would likely be the strongest and easiest to detect with our current technology?

• a signal used for local communication in the world where the intelligent beings exist
• an intentional signal beacon
• a signal used for communication between a civilization's home world and another star system
• a signal used for communication between a civilization's home world and another planet in its own planetary system

Question 26. Which of the following is the least-serious difficulty associated with interstellar travel and a timely colonization of the galaxy?

• the speed of light being the fastest possible speed we can travel
• Time dilation and length contraction due to Special Relativity
• the enormous amount of energy required to accelerate any ship to high speed
• the huge distances between the stars

Question 27. About how long would it take our fastest moving probes to travel the distance to the nearest stars?

• about a 1,000 years
• at least 100,000 years
• around 4.4 years
• several billion years

Question 28. Given how many times intelligent civilizations could have appeared over the universe's history, it is most likely that if other civilizations exist, they will

• have about the same level of technology as us
• be slightly less advanced than us
• be much more advanced than us
• be much less advanced than us

Question 29. What is the biggest limitation of using a solar-sail-propelled spacecraft to travel between stars?

• low energy photons that the Sun produces
• fact that the intensity of sunlight falls off rapidly with distance
• gravitational force of the Sun
• mass of the spacecraft

Question 30. Fermi Paradox could be resolved by all the following except:

• no one is interested or able to communicate
• intelligent species usually kill themselves off
• we are not interested in communicating
• no one is out there
• we are unable to detect their communications

Question 31. Which best describes the concept between a "wormhole"?

• shortcut between two distant parts of the universe through spacetime allowed by Einstein's General Theory of Relativity
• passageway to a parallel universe through a black hole explored by Einstein
• way of traveling faster than the speed of light locally relative to the fabric of spacetime
• shortcut between two distant parts of the universe through a black hole

Question 32. How is the "Fermi Paradox" normally stated?

• Who are we?
• Why are we here?
• Where are we?
• Who are you?
• Where is everybody?

Question 33. A nearby exoplanetary system is approximately 9 light-years away. If we send a spacecraft to visit this system traveling at 90% of the speed of light, how long will a round trip take as measured from the Earth?

Note: you don't need a fancy equation to solve this, just think which answer is most true based on the example of the twin paradox.

• 18 years
• less than 18 years
• about 20 years
• it's impossible to tell unless we know the spacecraft's method of propulsion

Question 34. In Einstein's Special Theory of Relativity, we observe time moving slower when an object travels at a speed near the speed of light.. This is called:

• time dilation
• a time warp
• time expansion
• time contraction

Question 35. We can calculate the energy needed to accelerate a colony spaceship based on what:

• its mass and final velocity
• its final velocity only
• the type of fuel it uses
• its mass only

Question 36. This question is similar to the one in the practice exam but with different numbers.

• Using the radial velocity method, what is the maximum radial velocity amplitude (in METERS/SECOND) you can measure for a star with an
• earth-mass planet in a 2.0 year circular orbit around a 0.5 solar mass star?
• For this problem, you can use the Earth weighs 1/333000 times the sun. 1 AU = 150e6 km
• Give yours answer in meters/second with at least 2 sig digits.

Question 37. If we consider the inner edge of the Habitable Zone to be 0.95 au today, where will it be when the Sun evolved to have a luminosity of 4x higher than today?

Question 38. Astronomers discover a Sun-like star with transit depth f_dip = 0.0025

What is the radius of this new planet in units EARTH RADII?

Question 39. The Earth orbits the Sun with a speed of about 30 km/s. What speed does the Earth induce on the Sun, assuming the Sun is 333000 x more massive than the Earth?

Your answer should be in units of METERS/SECOND:

Use 2 significant digits or more

Question 40. Consider a star that is half the size of the Sun. How deep (in %) would a transit be for a planet that is the size of Jupiter? Give your answer in terms of the percentage dip (not fraction).

Question 41. A Jupiter-mass planet is observed by European Extremely Large Telescope orbiting a nearby star with period of 10 years with a semi-major axis of 10 au. From this, we determine the mass of the host star to be what (in units of solar masses)?

Question 42. Astronomer's estimate the mass of the star 51 Peg to be 1.11 M_sun. The planet 51 Peg b is observed to have an period of 4.23 DAYS. Using Newton's version of Kepler's Third Law, what is the semi-major axis of the 51 Peg b orbit in au (astronomical units):

[use 2 sig digits]