Unit 4

Which of the following statements about a Type II Supernova is true?

A Type II supernova occurs at the end of the life of a star with 10 times the mass of our Sun or more

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

Alpha Centauri

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

orbited so close to its star it took only 4 days to go around

When a light wave leaves a region of strong gravity, compared to the same wave leaving a spaceship in empty space, the wave in strong gravity will have

-a gravitational redshift -less energy -a lower frequency -a longer wavelength

Which of the following descriptions of interstellar dust is FALSE?

-interstellar dust must be at a temperature equal to the outer layers of a star

Which of the following is the smallest?

neutron star

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?

Earth-sized planets are common, but so are planets somewhat bigger than Earth

Our solar system has 8 planets orbiting the Sun. Based on the discoveries of exoplanets so far, what can we say about a star with 8 planets?

Even though planets were only discovered starting in 1995, so we can't yet find planets that take centuries to go around their star, we already know other stars with 8 planets and we are likely to find more

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

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

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)?

Such planets make dips in the light of the star that are too small for Kepler to detect

Because white dwarfs are small, as their name implies, they are hard to see. What is a way astronomers have to find white dwarfs that distinguishes them from main sequence stars?

because white dwarfs get really hot, we can search for their ultraviolet radiation

When one member of a binary star system is a black hole, and astronomers detect flickering x-rays coming from the system, where are these x-rays usually coming from?

from a disk of material around the black hole (material that has been pulled from the companion star and is falling toward the black hole)

A handsome, rich, but vain movie star notices that he is starting to age, and consults you as his astronomy expert, to see if you can find an astronomical way to slow down his aging. Putting aside practical considerations (such as the fact that we cannot travel to other stars), which of the following strategies would IN THEORY allow him to age more slowly than the rest of humanity.

he should travel to a black hole, and spend some time in orbit just above the event horizon

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

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

To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at?

mass

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"

must have formed further out from the star and must have "migrated inward" early on

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

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

Astronomers observe a young cluster of stars, where stars with three times the mass of the Sun are still on the main sequence of the H-R diagram. Yet the cluster contains two white dwarfs, each with a mass less than 1.4 times the mass of the Sun. If we can show that the white dwarfs are definitely part of the cluster, how can their presence so soon in the life of the cluster be explained?

some stars can lose a lot of mass on their way to becoming white dwarfs; thus the white dwarfs could have started out as quite massive stars

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?

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

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

the angle at which the planet's orbit is tilted relative to us

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

the cores within the clumps of molecular clouds

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

the disks show lanes that are empty of dust within them

How did Supernova 1987A demonstrate that new elements are made in supernova explosions?

the light output was kept at high levels by the energy released from radioactive elements that decay very quickly; these must have been made by the supernova

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?

the lines come from interstellar matter between us and the star, not from the stars themselves

According to Einstein's general theory of relativity, the stronger a star's gravity,

the slower time runs near it

When neutron stars were first predicted theoretically, no scientist expected to be able to detect one of them across interstellar distances. What enabled astronomers to find neutron stars in the late 1960's?

we found strongly magnetic neutron stars whose whirling beams of energy were detected as pulsars

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?

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

Which of the following can a black hole not "eat" (swallow)?

you can't fool me, black holes can eat anything