Deck 21: The Birth of Stars and the Discovery of Planets Outside the Solar System

Question 1

When a star settles down to a stable existence as a main-sequence star, what characteristics determines where on the main sequence in an H-R diagram the star will fall?

A) its mass
B) the fraction of its atmosphere that consists of hydrogen
C) whether it is located on the outer regions or the central regions of the molecular cloud that gave it birth
D) the speed and direction of its rotation
E) the size of the disk around it

Answer 1

its mass

Question 2

Which of the following is NOT one of the reasons planets around other stars are so difficult to detect?

A) planets don't give off their own light, but only reflect the light of their stars
B) planets are small compared to stars, and so don't have much surface area from which to reflect light
C) from far away, planets are typically lost in the glare of their parent star
D) planets have much less mass than stars
E) planets only form very late in the life of a star, just when it is ready to die, and thus last only a very short fraction of the star's life

Answer 2

planets only form very late in the life of a star, just when it is ready to die, and thus last only a very short fraction of the star's life

Question 3

In figuring out the evolutionary tracks on the H-R diagram, astronomers

A) look at fossils from many times in Earth's history in a museum
B) observe one star over the course of several decades
C) make model stars on a computer and then follow how their characteristics will change with time
D) use big telescopes to observe how the outer layers of stars fall in during the protostar stage
E) send robot probes to the Sun

Answer 3

make model stars on a computer and then follow how their characteristics will change with time

Question 4

Which of the following are the small regions that are the embryos of stars (where individual stars are most likely to be born)?

A) local bubbles
B) the cores within the clumps of molecular clouds
C) HII regions
D) spiral galaxies
E) the parts of the interstellar medium where the temperature is millions of degrees

Question 5

What observations about disks of dusty material around young stars suggest that planets may be forming in such disks?

A) the disks give off x-rays and gamma-rays characteristic of small planets
B) the disks show lanes that are empty of dust within them
C) the disks show evidence of very strong winds coming from the star
D) the disks are making the stars "wiggle" -- move back and forth across the sky -- in a way that can be observed even with small telescopes
E) radio telescopes have revealed transmissions from the disks that include rap songs and other evidence of advanced civilizations
Section 21.4: Planets Beyond the Solar System: Search and Discovery

Question 6

Astronomers studying regions like the Orion Giant Molecular Cloud have observed that a wave of star formation can move through them over many millions of years. What sustains such a wave of star formation in a giant molecular cloud?

A) radio waves from complex molecules move slowly through the cloud, causing stars to form
B) when a group of stars form, they remove so much material from the cloud that only a big empty place is left, into which new matter from other clouds falls, making more stars
C) when massive stars form, their ultraviolet radiation and later their final explosions compress the gas in the cloud and cause a new group of stars to form
D) when giant molecular clouds collide with each other, they do so not just once, but many times
E) the dust in these clouds is so heavy, it is always settling inward toward the cloud's center causing star formation in its wake

Question 7

The first ordinary star (other than our own Sun) around which planets were definitely discovered was:

A) Alpha Centauri
B) Beta Pictoris
C) 51 Pegasi
D) Delta Cepheii
E) Ariana Grande

Question 8

Astronomers identify the "birth" of a real star (as opposed to the activities of a protostar) with what activity in the star?

A) when it starts to contract rapidly from a cloud of gas and dust
B) when it first becomes visible inside its dust cloud
C) when a wind is observed coming from its surface
D) when nuclear fusion reactions begin inside its core
E) when it glows with infrared radiation

Question 9

If you want to find stars that are just being born, where are the best places to search?

A) in HII regions
B) in giant molecular clouds
C) in regions of ultra-hot interstellar hydrogen gas
D) in the disks around massive stars that were just recently formed
E) Hollywood

Question 10

If an astronomer wants to find and identify as many stars as possible in a star cluster that has recently formed near the surface of a giant molecular cloud (such as the Trapezium cluster in the Orion Nebula), what instrument would be best for her to use?

A) an infra-red telescope (and camera)
B) an x-ray telescope
C) a very good camera attached to a large reflector telescope on the ground
D) an ultraviolet spectrograph attached to the Hubble Space Telescope
E) the instruments that were part of the Compton Gamma Ray Observatory

Question 11

A star whose temperature is increasing but whose luminosity is roughly constant moves in what direction on the H-R diagram?

A) to the right
B) to the left
C) upwards
D) downwards
E) you can't fool me; stars don't move on the H-R diagram

Question 12

A graduate student is given the assignment to find stars with dusty disks around them. What kind of telescope would it be best for her to use for this purpose?

A) a small telescope that detects visible light
B) a large telescope that detects infrared radiation
C) any telescope that can detect x-rays
D) an orbiting telescope that can detect ultra-violet rays
E) the students should worry; any telescope can easily show such dusty disks

Question 13

Why is it so difficult for astronomers to see new stars in the process of birth?

A) birth happens very quickly, so it is hard to "catch" stars "in the act"
B) most stars are born inside dusty clouds, which block any light that may be coming from the stars
C) the size of a newly forming star is typically quite small and thus hard to make out
D) protostars which are not yet doing fusion do not give off a lot of visible light
E) all of the above

Question 14

Which of these stars will take the SHORTEST time to go from the earliest protostar stage to the main sequence?

A) a star 1/10^th the mass of our Sun
B) a star ½ the mass of our Sun
C) a star equal to the mass of our Sun
D) a star ten times the mass of our Sun
E) all of these stars take the same time to get to the main sequence
Section 21.3: Evidence that Planets Form Around Other Stars

Question 15

The Orion Nebula is

A) a distant galaxy of stars and raw material
B) a small disk of gas and dust surrounding a single star that was recently formed
C) a large cloud of gas and dust illuminated by the light of newly formed stars within it
D) the remnant of a star that exploded several thousand years ago
E) an illusion caused by activity in the Earth's upper atmosphere

Question 16

You are an astronomy graduate student and you are observing the big Orion Nebula from an airplane that has a good-sized infrared telescope built into it (there really is such a plane.) On an infrared image of the Nebula, what would particularly stand out?

A) the stars that are visible in our sky as the constellation of Orion
B) HII regions (ionized hydrogen regions) in the Nebula
C) the clouds of the nebula that have a lot of dust in them
D) hot Jupiters close to their stars
E) none of the above

Question 17

What technique did astronomers use to make the first confirmed discovery of a planet around another star like the Sun?

A) block out the light of the star and take a photograph of the fainter planet
B) measure the position of the star on the sky very carefully over many years and search for small wiggles in its position due to the gravitational pull of a planet
C) measure the Doppler shift of the lines in the star's spectrum and look for periodic changes in this shift due to the pull of the planet as it orbits the star
D) search for the presence of metallic and rocky elements in the spectrum of the star
E) look for a small dip in the light of the star when the planet crosses its disk

Question 18

A Herbig-Haro (HH) object is

A) a small galaxy just outside the outer edge of the Milky Way
B) where a jet from a star in the process of being born collides with (and lights up) a nearby cloud of interstellar matter
C) a part of a giant molecular cloud where molecules containing two hydrogen atoms form
D) a star that has too little mass to start fusion in its core
E) cluster of very low-mass stars, observable only with infrared radiation

Question 19

Astronomers call a ball of matter that is contracting to become a star

A) a Herbig-Haro object
B) a giant molecular cloud
C) a planet
D) a protostar
E) a main sequence star

Question 20

Astronomers believe that disks of material will form around protostars that are spinning. Which of the following observed phenomena is a good indication of the presence of a disk around a protostar?

A) HII regions
B) huge pillars of dust, like those seen by the Hubble in the Eagle Nebula
C) jets and Herbig-Haro objects
D) the presence of molecules in giant clouds of gas and dust
E) gamma rays detected from the direction of giant molecular clouds
Section 21.2: The H-R Diagram and the Study of Stellar Evolution

Question 21

With our current techniques, astronomers can typically only measure the minimum mass of a planet orbiting another star. To know the precise mass of the planet, they must also be able to determine

A) the age of the star
B) the angle at which the planet's orbit is tilted relative to us
C) whether the planet has any moons
D) the time the planet takes to make one orbit
E) the language the planet's inhabitants speak, so we can ask them

Question 22

How did astronomers determine that the planet orbiting the star HD 209458 is a gas giant like Jupiter and not made mostly of rocks or metals?

A) they looked for light from the planet reflected into the spectrum of the star
B) they measured the mass of the planet, which immediately told them whether it was gas or rock
C) they watched the planet eclipse (cover) the light of the star, and thus were able to get the planet's size
D) they knew that any planet as close to its star as this one was could not be made of rock or metal
E) it took more than one of the above measurements to figure out this problem
Section 21.5: Exoplanets Everywhere - What We Are Learning

Question 23

Planets in the habitable zone of their stars:

A) are always the planets closest to the star
B) are also called hot Jupiters
C) are so far from their stars that it is very difficult to discover them
D) are at a temperature where water can exist as a liquid
E) cannot exist around stars that are red dwarfs (spectal type M)
Section 21.6: New Perspectives on Planet Formation

Question 24

The closest star to the Sun, Proxima Centauri, was recently found to have a planet in its habitable zone. Proxima Centauri is a main sequence star with spectral type M. How would its habitable zone differ from the habitable zone of our Sun?

A) it would be significantly closer to Proxima Centauri than ours is to the Sun
B) it would be significantly further away from Proxima Centauri than our is to the Sun
C) it would be in the same position as our habitable zone, but be much wider
D) it would be in the same position as our habitable zone, but be much thinner
E) this question can't be answered until we send a probe to Proxima Centauri

Question 25

Which of the following is a reason that astronomers have not found giant planets with the orbit of Neptune around other stars?

A) our theories suggest that orbits as far away from a star as Neptune are never stable (and the presence of Neptune in our own solar system is a big mystery)
B) Neptune takes 165 years to go around the Sun; getting information about just one cycle of such a planet's orbit around another star would take astronomers 165 years
C) at the orbit of Neptune, only very low-mass planets (smaller than Mercury) can form
D) the method we are using to find planets currently can only reveal low-mass planets, while we expect high-mass planets at the orbit of Neptune
E) you can't fool me; we have already found several planets as far from their stars as Neptune is from the Sun

Question 26

The star now called Kepler-444 is 11 billion years old (much older than the Sun) and has five planets orbiting close to it. What has this system taught astronomers about the history of star formation?

A) All old stars must have their planets orbiting very close to them; only much younger stars have planets far away (like our Jupiter)
B) If such an old star has planets close to it, where it's really warm, those planets must be made of heavier elements. So heavier elements must have formed before the time this star formed.
C) If planets formed so long ago, then by today all the heavy elements must be exhausted; this means rocky planets can no longer form in the Galaxy
D) Stars like Kepler-444 are old and exceptional. Today, stars have much more trouble forming more than one planet, and certainly never form five at a time.
E) Kepler-444 must have collided with another star and "stolen" its planets; no star could possibly have had planets this early in the history of the Galaxy

Question 27

The first (living) star other than our own Sun found to have more than one planet orbiting it is called

A) Upsilon Andromedae
B) Beta Pictoris
C) Alpha Centauri
D) 51 Pegasi
E) Sirius

Question 28

Astronomers were surprised to find so many Jupiter-mass planets so close to their stars. According to their best theories and models, such "hot Jupiters"

A) must have formed close to their stars, but only billions of years after the star formed
B) must have been captured from a passing star that got very close
C) must be falling into their stars and will soon be vaporized
D) must have formed further out from the star and must have "migrated inward" early on
E) are absolutely impossible, so they must be mistaken observations

Question 29

An astronomy class is so excited by the discovery of planets around other stars that they decide to do a library exhibit on the subject so that everyone in the school can learn about it. In this exhibit they want to pay tribute to both the astronomers of today who have done the work AND some of the scientists of the past whose work was essential to making the discoveries possible (and directly related to the techniques involved). Which of the following scientists of the past should definitely be included in the exhibit?

A) Christian Doppler
B) Gerard Kuiper
C) Ptolemy
D) George Herbig
E) Ejnar Hertzsprung

Question 30

Why was the Kepler mission not able to find planets smaller than Mars, even though it was in space (and had no Earth atmosphere to deal with)?

A) Such planets always take longer to orbit their stars than the time the mission lasted
B) Such planets make dips in the light of the star that are too small for Kepler to detect
C) Such planets are only ever detectable using the Doppler shift method
D) Such planets are red in color, and Kepler's cameras could not see red objects
E) Astronomers believe that planets smaller than Mars could not exist

Question 31

The big surprise about the first planet discovered around another regular star was that it

A) was smaller than Mercury or Pluto in our own solar system
B) orbited so close to its star it took only 4 days to go around
C) had a mass greater than that of most stars
D) had a spectrum which indicated it was made of elements we never find on Earth
E) was inhabited by intelligent creatures which never had to take astronomy exams

Question 32

The telescope that allowed astronomers to discover most of the planets found with the transit method was called

A) the Hubble Space Telescope
B) the Kepler mission
C) the Keck Telescope
D) the Very Large Array of radio telescopes
E) you can't fool me; just about any telescope can show us many, many planet transits

Question 33

When astronomers carefully examine the planets found by Kepler and draw conclusions from the Kepler sample, what do they conclude about planets the size of Earth?

A) Earth-sized planets are very rare in the Galaxy; our system is lucky to have one
B) Earth-sized planets are the main kind of planets found by far; Jupiter and Neptune sized planets are so rare, they almost never show up in our discoveries
C) Earth-sized planets are common, but so are planets somewhat bigger than Earth
D) Earth-sized planets are only found in systems that also have hot Jupiters
E) none of the above

Question 34

To measure how dense a planet is (to know whether it is made of rock or gas and liquid) they must be able to measure the planet's mass from the Doppler shift and

A) the planet's temperature from its spectrum
B) the planet's velocity (speed) toward or away from us
C) the planet's radius using the transit method
D) the planet's color from photographs
E) whether the planet has rings around it or not