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Which two energy sources can help a star maintain its internal thermal pressure?
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No stars are expected with masses greater than 300 times our Sun because
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Chapter 10
Astronomy
| Question | Answer |
|---|---|
| Which two energy sources can help a star maintain its internal thermal pressure? | nuclear fusion and gravitational contraction |
| No stars are expected with masses greater than 300 times our Sun because | they would generate so much power that they would blow themselves apart. |
| As a solar mass protostar moves on to the main sequence, | its surface temperature increases and its luminosity decreases. |
| When does a star become a main-sequence star? | when the rate of hydrogen fusion in the star's core is high enough to sustain gravitational equilibrium |
| Which of the following statements about degeneracy pressure is not true? | Degeneracy pressure varies with the temperature of the star. |
| What is a protostar? | A star that is still in the process of forming |
| What kind of gas cloud is most likely to give birth to stars? | A cold, dense gas cloud |
| When does a protostar become a main-sequence star? | When the rate of hydrogen fusion becomes high enough to balance the rate at which the star radiates energy into space |
| Since all stars begin their lives with the same basic composition, what characteristic most determines how they will differ? | mass they are formed with |
| A star's luminosity is the | total amount of energy that the star radiates each second. |
| According to the inverse square law of light, how will the apparent brightness of an object change if its distance to us triples? | Its apparent brightness will decrease by a factor of 9. |
| If the distance between us and a star is doubled, with everything else remaining the same, its luminosity | remains the same, but its apparent brightness is decreased by a factor of four. |
| Which of the following correctly states the relationship between the apparent brightness, luminosity, and distance of a star? | apparent brightness = luminosity 4 (distance)2 |
| You measure the parallax angle for a star to be 0.1 arcseconds. The distance to this star is | 10 parsecs. |
| Which of the following terms is given to a pair of stars that appear to change position in the sky, indicating that they are orbiting one another? | visual binary |
| Which of the following best describes the axes of a Hertzsprung-Russell (H-R) diagram? | surface temperature on the horizontal axis and luminosity on the vertical axis |
| On the main sequence, stars obtain their energy | by converting hydrogen to helium. |
| Assuming that we can measure the apparent brightness of a star, what does the inverse square law for light allow us to do? | Calculate the star's luminosity if we know its distance, or calculate its distance if we know its luminosity. |
| If Star A is closer to us than Star B, then Star A's parallax angle is ________. | larger than that of Star B |
| Which of the following terms is given to a pair of stars that we can determine are orbiting each other only by measuring their periodic Doppler shifts? | Spectroscopic binary |
| How is the lifetime of a star related to its mass? | More massive stars live much shorter lives than less massive stars. |
| What is the common trait of all main sequence stars? | They generate energy through hydrogen fusion in their core. |
| What is a white dwarf? | The remains of a star that ran out of fuel for nuclear fusion |
| All stars are born with the same basic composition, yet stars can look quite different from one another. Which two factors primarily determine the characteristics of a star? | Its mass and its stage of life |
| Based on the definition of apparent brightness, which units are appropriate for its measurement? | Watts per square meter |
| Star A is identical to Star B, except that Star A is twice as far from us as Star B. Therefore: | Both stars have the same luminosity, but the apparent brightness of Star B is four times that of Star A. |
| To calculate the masses of stars in a binary system, we must measure their ________. | orbital period and average orbital distance |
| Which of the following comparisons between low-mass stars and high-mass stars is true? | Low-mass stars are cooler and less luminous than high-mass stars. |
| Astronomers can measure a star's mass in only certain cases. Which one of the following cases might allow astronomers to measure a star's mass? | The star is a member of a binary star system. |
| What are the standard units for luminosity? | Watts |
| What type of star is our Sun? | A low-mass star |
| No stars are expected with masses greater than 300 times our Sun because | they would generate so much power that they would blow themselves apart. |
| What is the fate of an isolated brown dwarf? | It will remain a brown dwarf forever. |
| It will remain a brown dwarf forever. | Every object emits thermal radiation with a spectrum that depends on its temperature. |
| What is not a property of thermal radiation? | Hotter objects emit photons with a lower average energy. |
| Which of the following terms is given to a pair of stars that orbit in the plane of our line of sight.? | Eclipsing binary |
| What is a molecular cloud? | All of the above |
| What is the interstellar medium? | The gas between the stars |
| What of the following happen during the star birth? | all of them |
| Jets are observed coming from | the centers of disks around protostars. |
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