Chapter 21

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

a large cloud of gas and dust illuminated by the light of newly formed stars within it

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

a protostar

Which of these stars will take the SHORTEST time to go from the earliest protostar stage to the main sequence? a. a star 1/10th 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

a star ten times the mass of our Sun

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

all of the above

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

an infra-red telescope (and camera)

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

in giant molecular clouds

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

its mass

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

jets and Herbig-Haro objects

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

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

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

the clouds of the nebula that have a lot of dust in them

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

the cores within the clumps of molecular clouds

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

to the left

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

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

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

when nuclear fusion reactions begin inside its core

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

where a jet from a star in the process of being born collides with (and lights up) a nearby cloud of interstellar matter