Star Quiz
Questions: 16 · 10 minutes
1. After a Sun-like star becomes a red giant and sheds its outer layers, what does its exposed core generally become?
A brown dwarf
A new protostar
A white dwarf
A main-sequence blue giant
2. One stellar nursery contains gas enriched by material expelled from earlier generations of stars. Compared with the earliest stars, what is more likely to be present in its new stars?
Only elements created during planet formation
No hydrogen or helium at all
A greater proportion of elements heavier than helium
Matter unaffected by any previous stellar activity
3. Which force is chiefly responsible for pulling gas and dust together during star formation?
Gravity
Magnetism
Friction
Radioactive decay
4. A very massive star exhausts its nuclear fuel and its core collapses. Which outcome is most consistent with this event?
It quietly becomes a rocky planet
It may explode as a supernova and leave a neutron star or black hole
It settles into an ordinary white dwarf without ejecting material
It returns directly to the protostar stage
5. A collapsing protostar becomes smaller while its internal pressure and temperature increase. What best explains the heating?
The surrounding cloud reflects the protostar’s light back into its core
The protostar absorbs most of its heat from nearby mature stars
Cold hydrogen atoms spontaneously become hot helium without compression
Gravitational energy is converted into thermal energy as the material contracts
6. A young star is hidden inside a thick dusty cloud. Which observing strategy is often most useful for studying it?
Use only visible light because dust is transparent at visible wavelengths
Search only for reflected sunlight from the young star
Wait until the entire cloud becomes a solid surface
Observe at infrared wavelengths, which can pass through dust more effectively than visible light
7. A main-sequence star remains roughly stable in size for a long period. Which balance makes this possible?
Magnetic attraction inward balances orbital motion outward
Inward gravity balances outward pressure associated with the hot interior
Dark matter pressure balances radiation arriving from other stars
The pull of planets balances the pull of the star’s core
8. Astronomers spread a star’s light into a spectrum and identify a pattern of dark absorption lines. What can the pattern help reveal?
The exact number of planets in the star’s system
Chemical elements present in the star’s atmosphere
The shape of the star’s solid surface
The future positions of every nearby galaxy
9. In which environment do most stars begin forming?
Cold, dense regions within molecular clouds
The hot outer layers of existing stars
Nearly empty regions between galaxies
The event horizons surrounding black holes
10. Gas falling toward a protostar forms a flattened, rotating disk instead of dropping straight into the center. What best explains this shape?
Nuclear fusion pushes all material into a perfectly flat plane
The protostar’s gravity stops acting above and below its equator
Conservation of angular momentum makes rotating material form an accretion disk
Radiation removes all motion from the infalling gas
11. What is a protostar?
A forming star that has not begun stable hydrogen fusion
A planet that is gradually becoming a star
A stellar remnant left after a supernova
A mature star that has exhausted its core hydrogen
12. What process supplies most of a main-sequence star’s energy?
The burning of ordinary material in oxygen
The splitting of heavy atomic nuclei
The continued collision of planets with the star
The fusion of hydrogen into helium in the core
13. Two stars appear equally bright from Earth and are at the same distance. One looks blue and the other red. What can generally be inferred about their surface temperatures?
The blue star has the higher surface temperature
The red star has the higher surface temperature
Their colors show that both have identical temperatures
Color is unrelated to stellar surface temperature
14. A molecular cloud is not perfectly uniform: some regions are denser than others. Why can this encourage the formation of multiple stars?
Every dense region immediately begins nuclear fusion at the same temperature
Dense regions repel one another and become isolated stars
The cloud’s atoms change directly into fully formed stars
Separate dense clumps can collapse under their own gravity
15. On a Hertzsprung–Russell diagram, two main-sequence stars are compared. One has a much higher surface temperature. What is generally also true of that star?
It must be older than every cooler main-sequence star
It is generally more luminous
It must already have become a white dwarf
It produces energy without nuclear fusion
16. A newly discovered object formed like a star but never became massive and hot enough for sustained hydrogen fusion. How should it be classified?
A white dwarf
A neutron star
A brown dwarf
A red giant