Deck 20: Between the Stars

Question 1

Astronomers were at first surprised to find complicated molecules in the interstellar medium. They thought ultra-violet light from stars would break apart such molecules. What protects the molecules we observe from being broken apart?

A) such molecules form in cells, and there is a protective membrane around each cell
B) such molecules always form inside stars; the stars outer layers protect them
C) such molecules form in clouds that contain significant amounts of dust, and the dust in the cloud protects them from ultra-violet rays
D) such molecules form only in the regions that are already millions of degrees hot and thus can't be affected by ultra-violet rays
E) you can't fool me; the seeming discovery of complex molecules out there was a mistake, and astronomers now realize there are no molecules out there.

Answer 1

such molecules form in clouds that contain significant amounts of dust, and the dust in the cloud protects them from ultra-violet rays

Question 2

If an astronomer wanted to find some relatively complex molecules in space, what technique should she use?

A) point a gamma-ray telescope toward the center of the Milky Way Galaxy
B) take a spectrum of the visible light coming from our own Sun
C) point a radio telescope into regions in the galaxy where there is a lot of dust
D) use an ultra-violet telescope above the Earth's atmosphere to find highly ionized atoms
E) use the Hubble Space Telescope to take many visible-light images of faint nebulae

Answer 2

point a radio telescope into regions in the galaxy where there is a lot of dust

Question 3

An astronomer wants to observe a cloud of dust in a relatively close part of the Galaxy. Unfortunately, this dust cloud is not located in the direction of a crowded region of stars. What instrument would be the most help in finding this cloud.

A) a visible-light telescope (like the Keck) with a camera or CCD detector
B) an x-ray telescope in orbit around the Earth
C) a giant vat of cleaning fluid deep in a mine-shaft
D) a sensitive infra-red telescope in orbit around the Earth
E) a spectroscope that can search for the line radiation from highly ionized atoms

Answer 3

a sensitive infra-red telescope in orbit around the Earth

Question 4

You are observing a binary star system and obtain a series of spectra of the light from the two stars. In this spectrum, most of the absorption lines shift back and forth as expected from the Doppler Effect. A few lines, however, do not shift at all, but remain at the same wavelength. How can we explain the behavior of the non-shifting lines?

A) there is a star in the system which is not moving at all: it is just sitting there
B) there is a planet orbiting the stars in the system
C) there are huge clouds of dust just behind this star system from our perspective
D) the lines come from interstellar matter between us and the star, not from the stars themselves
E) there is no explanation of this behavior: it is an unsolved mystery in science

Question 5

A friend of yours who has not taken an astronomy class looks at your textbook and really likes the picture of the Pleiades, a cluster of stars surrounded by a bluish reflection nebula. She wants to know what causes that beautiful blue glow. To explain it to her, you want to compare the process that causes the blue glow to something that is in your friend's everyday experience. Which of the following terrestrial phenomena is the result of the same type of process that makes a reflection nebula in space?

A) the blueish glow of the flame on a gas stove
B) the blue light you see reflected from a blue sweater
C) the blue color of the Earth's sky
D) the blue-white color of the hottest stars
E) the blue feeling you get when you don't do well on an astronomy exam

Question 6

An HII region is

A) a zone around a hot star where hydrogen atoms are ionized
B) a place where there is mostly neutral hydrogen whose spectral lines we observe
C) a cloud of dark dust, which absorbs much of the starlight coming from behind it
D) one of the large and cold molecular clouds where we see star formation going on
E) a cloud of complex molecules, such as alcohol and formaldehyde

Question 7

Which of the following is NOT a way astronomers discover clouds of interstellar matter that have a large amount of dust in them?

A) by blocking the light of stars behind them
B) by reflecting nearby starlight
C) because they make stars behind them look redder than they should be
D) by giving off infrared radiation appropriate to their temperature
E) by giving off x-rays from hot gas surrounding the dust cloud

Question 8

When astronomers discuss a nebula, what are they talking about?

A) the Frisbee-shaped collection of gas that covers the entire Milky Way Galaxy
B) the cloud of comets that lies on the outskirts of the solar system
C) a giant cloud of gas and dust between or among the stars
D) a star surrounded by at least 8 planets and many moons
E) none of the above

Question 9

Astronomers have found large quantities of cold, neutral hydrogen gas in our galaxy. How is this gas distributed?

A) it is located only near stars, and not in the large empty spaces between them
B) it is found mostly in a flat layer extending throughout the disk of our galaxy
C) it is found in a spherical distribution about 100 LY in size, centered on the Sun
D) it is found only in the outer regions of the galaxy, where we are, and not in the central areas
E) we don't know its distribution, since such cold hydrogen cannot be observed with the techniques we have at our disposal today

Question 10

How do fragile structures like acetaldehyde (CH₃CHO) molecules survive in the harsh environment of interstellar space? Why are they not destroyed by high-energy radiation from stars?

A) such molecules are only found in the shadows of the stars
B) such molecules are found only on planets or comets, not in space
C) such molecules are protected by the presence of hot interstellar hydrogen
D) such molecules are found only in dense clouds that have a lot of dust; the dust keeps the radiation from hot stars from reaching the molecules
E) such molecules are found only where very cool stars are present, that's why they are so very rare in the Galaxy
Section 20.3: Interstellar Dust

Question 11

You are an astronomer whose supervisor has just forbidden drinking alcoholic beverages near the observatory. In frustration, you under?take a search for alcohol molecules in space. Where would your search be most likely to succeed?

A) in an interstellar cloud of gas and dust
B) in a binary star system
C) in the surface layers of our Sun, which is the nearest star
D) in a region of ionized hydrogen near an O type star
E) you can't fool me; no one has observed alcohol in space

Question 12

Which of the following statements about interstellar matter is FALSE?

A) 99% of it is in the form of gas
B) it is clumpy: much of it is distributed in patchy, irregular clouds
C) the total mass in interstellar matter in our Galaxy is about 5% of the mass in stars
D) if the matter were spread out evenly, it would be about as dense as the Earth's atmosphere
E) it also includes grains of dust

Question 13

An astronomer wants to observe a cloud of cold neutral (not ionized) hydrogen, far away from any stars. What would be an instrument that could help in this task?

A) a telescope in space, able to pick up x-rays from space
B) a radio telescope, tuned to a wavelength of about 21 centimeters
C) a large telescope observing visible light, but with a very sensitive CCD detector attached
D) a neutrino detector, deep underground
E) you can't fool me; there is no way to observe clouds of hydrogen that are not near a star

Question 14

The red color we see on a lot of photographs of nebulae comes from which element?

A) helium
B) oxygen
C) carbon
D) hydrogen
E) not an element at all, but the molecule carbon dioxide

Question 15

Astronomers now understand that the dark regions or rifts visible in parts of our Galaxy that are otherwise crowded with stars are caused by:

A) the absence of stars in regions that have been cleared out by recent explosions
B) starlight being blocked by otherwise invisible planets at the outskirts of our solar system
C) clouds with a considerable amount of dust which blocks the light of the stars behind them
D) huge groups of stars that only give off radiation in the infrared and not in visible light
E) holes in the structure of our Galaxy

Question 16

What happens in the process of fluorescence?

A) water molecules are broken up into hydrogen and oxygen
B) atoms absorb ultraviolet rays and convert them to visible light as their electrons cascade to lower energy levels
C) hydrogen is transformed into helium where gas is very, very hot
D) radio waves are given off as molecules change their vibration or rotation
E) fluorine gas is released by chemical reactions in the outer layer of a star

Question 17

Supposing we launched a very fast dart from the Space Shuttle, pointed in some direction away from any planet, so that it could travel beyond the solar system. What would it be most likely to hit first after traveling outward for a while?

A) a star other than the Sun
B) an exoplanet
C) an atom of interstellar gas
D) another galaxy
E) its chances of intersecting all of the above is about the same
Section 20.2: Interstellar Gas

Question 18

Astronomers use the term interstellar matter to refer to:

A) planets around stars other than the Sun
B) comets, asteroids, and meteors
C) gas and dust that lies between stars
D) electro-magnetic radiation coming from a group of stars
E) a fortune teller who says she is from outer space

Question 19

In order for a cold atom of hydrogen to emit a 21-cm wave, it must first be in a slightly higher energy state. What event usually "kicks" the hydrogen atom up to this higher state?

A) waves of ultraviolet energy from hot stars pass by a cold gas cloud
B) a gas cloud collapses under its own gravity until it is much smaller than it originally was
C) gas atoms within the cloud collide
D) hydrogen is ionized by other waves
E) some alcohol molecules within the cloud lead to a wild party

Question 20

Some of the interstellar gas in our Galaxy has been heated to millions of degrees, a temperature that surprised astronomers when it was first discovered. How do we now think that gas between stars gets that hot?

A) any gas close to a star will naturally get that hot
B) very powerful shock waves from exploding stars heat the gas they come into contact with
C) gas gets to be this hot when hydrogen atoms flip their spin and give off 21-cm radiation
D) such gas is heated by the radiation given off by complex molecules in clouds
E) astronomers have no idea how gas gets this hot; this is an unsolved mystery in astronomy

Question 21

The Local Bubble is

A) a region of low density interstellar gas extending several hundred LY around the Sun
B) a region around any exploding star where material is expanding from the explosion
C) another name for the Milky Way Galaxy
D) the region around very hot stars where hydrogen is ionized
E) a night club specializing in champagne located in Bayonne, New Jersey

Question 22

Where is the outer rim of the Local Bubble located today?

A) pretty much where Pluto orbits the Sun
B) about 200 light-years from the Sun, in the rough direction of the constellations of Orion, Perseus, and Auriga
C) at the edge of the Milky Way Galaxy
D) at the edge of the Orion Nebula
E) where else? Bayonne, New Jersey

Question 23

Cosmic rays are

A) high-energy electro-magnetic radiation
B) fast-moving dust grains
C) neutrinos of various types
D) highly reddened light emerging from dust clouds
E) high-speed atomic nuclei, electrons, and positrons

Question 24

The amount of interstellar matter present in our Galaxy is always changing. Which of the following processes is NOT a major contributor to that change?

A) gas from outside the Galaxy falls into the Milky Way because of gravity
B) the powerful explosions that end the lives of massive stars drive material out of the Galaxy
C) interstellar matter in dense clouds collapses into stars and is taken "out of circulation"
D) some atoms of gas combine in dusty clouds to make more complex molecules
E) actually, none of the above is a major contributor to the change

Question 25

Astronomers use the term interstellar extinction to refer to:

A) the death of the dinosaurs and other species from the collision of an asteroid with the Earth
B) the death of a massive star when it explodes
C) the ionization of a region of hydrogen around an extremely hot star
D) the absorption of radio waves at 21-cm by cold hydrogen atoms
E) the scattering and absorption of starlight by dust grains in space

Question 26

The light element lithium (which, on Earth, is part of medications that improve the lives of people with mental health illnesses) is more common in cosmic rays than it is in the Sun and the stars. What do astronomers think is the reason for this?

A) there is a lot of lithium (and other light elements) in interstellar dust
B) lithium is so easy to fuse, its fusion happens outside of stars in hot HII regions
C) because cosmic rays move so fast, they can collide with atoms of carbon, nitrogen, and oxygen and break them apart, producing more light elements like lithium
D) lithium is radioactive; its nucleus decays (falls apart) very quickly
E) this is an unsolved problem in astronomy
Section 20.5: The Life Cycle of Cosmic Material

Question 27

An astronomer is observing a star which puzzles her. The lines in the star's spectrum indicates that the star is very hot and should therefore be blue. But the star looks reddish in photographs and in measurements of the continuous spectrum. What is one possible explanation of this puzzle?

A) this star is surrounded by an HII region
B) this star is in a local bubble, just like the Sun
C) the star is no longer undergoing nuclear fusion inside
D) we are seeing the light of the star through layers of interstellar dust
E) this star must be located high above the disk of the Milky Way Galaxy

Question 28

Which of the following is not a place where astronomers believe interstellar dust grains can form?

A) in the cooling winds of material ejected from red giant stars
B) in the material flowing out of exploded stars, after it has cooled
C) in denser clouds of interstellar matter
D) in HII regions
E) all of the above are places where dust grains regularly form
Section 20.6: Interstellar Matter around the Sun

Question 29

The largest types of clouds found in interstellar space are

A) HI regions -- clouds of neutral hydrogen
B) molecular clouds with supplies of dust and molecules
C) HII regions -- clouds of ionized hydrogen
D) interstellar grains
E) all these clouds are approximately the same size

Question 30

The Messier Catalog is

A) a listing of all the stars within the Local Bubble
B) a list of all the HII regions visible without a telescope
C) a list of nebulae, star clusters, and galaxies that might be mistaken for a comet far from the Sun
D) a list of regions where dark clouds with large numbers of molecules can be found
E) the catalog that some graduate students accidentally dropped in the mud

Question 31

The term "baryon cycle," as astronomers use it, refers to:

A) the steps in the fusion of hydrogen into helium at the center of stars
B) the kinds of orbits short-period comets take around the Sun
C) the movement of interstellar material into the Galaxy and into stars and then the movement out when stars end their lives
D) the change of individual atoms into molecules in dusty interstellar clouds
E) exercise equipment they had in the White House for President Obama

Question 32

Cosmic rays differ from other forms of interstellar matter by

A) moving much faster, at typical speeds of 90% the speed of light
B) being made of hydrogen atoms
C) absorbing all the light that falls on them
D) having nothing to do with stars at any point in their "lives"
E) coming only from outside the Milky Way Galaxy

Question 33

Given the presence of dust throughout the disk of the Milky Way Galaxy, what is the best technique for learning about more distant regions of our galaxy's disk.

A) look for blue radiation from stars and nebulae, since the light is reddened
B) look for red light from stars and nebulae
C) look for radiation at long wavelengths, for example in the infrared region of the spectrum
D) look for HII regions, whose high-energy radiation penetrates dust
E) send a spacecraft to Pluto, from where we can see above the Galaxy's disk

Question 34

Why can astronomers not tell from what direction a particular cosmic ray started toward the Earth?

A) all cosmic rays are scattered by dust in interstellar space
B) we don't believe cosmic rays have a particular source; they have always been circulating around the Galaxy
C) cosmic rays are reflected by interstellar matter and thus are always reversing direction
D) cosmic rays are charged particles and are thus spiral around the Earth and the Galaxy's magnetic field
E) cosmic rays are very strongly Doppler shifted

Question 35

Which of the following descriptions of interstellar dust is FALSE?

A) interstellar dust has a (tiny) rocky core surrounded by an ice mantle
B) interstellar dust must be roughly the size of the wavelength of visible light
C) interstellar dust must be made of some of the most common elements in the universe
D) interstellar dust must be at a temperature equal to the outer layers of a star
E) interstellar dust particles can sometimes be found in meteorites and can be identified
Section 20.4: Cosmic Rays

Question 36

The dust in the dust clouds in interstellar space consists of

A) atomic gas
B) molecular gas
C) tiny solid grains
D) pieces of ice ranging from several meters to a kilometer in diameter
E) none of the above

Question 37

Among interstellar clouds, the hotter the cloud, the

A) the higher the density of particles in it
B) the smaller the diameter of the cloud must be
C) the lower the density of particles in it
D) less likely it is to contain ionized atoms
E) the more likely it is to contain vast quantities of complex molecules