Stellar evolution: initial mass changes the route
Đã giới thiệu| English | Ý nghĩa |
|---|---|
| main sequence/meɪn ˈsiːkwəns/ | Dãy chính |
| white dwarf/waɪt dwɔːf/ | Sao lùn trắng |
What would explain this observation?
- The Sun and a very massive star do not have the same final remnant. A life-cycle diagram must branch according to initial mass.
Build the model
- A star forms from a collapsing cloud of gas and dust.
- A stable main-sequence 主序 star releases energy by nuclear fusion, while gravity and outward pressure maintain its structure.
- A lower-mass star can pass through a red-giant stage to a white dwarf 白矮星; a sufficiently massive star can undergo a supernova and leave a neutron star or black hole.
- main sequence: A stable stellar phase sustained by core hydrogen fusion.
- white dwarf: A compact remnant on the lower-mass stellar route.
Which final route is appropriate for the Sun in the school model?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
In the school model the Sun's initial mass is below the threshold for a supernova: it will swell to a red giant, shed its outer layers and leave a white dwarf. Black holes and supernovae belong to much more massive stars.
Match each technical term to its precise meaning.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Read a life-cycle diagram as a model of stages and conditions, not a timed film of one star.
- The Sun is expected to follow the lower-mass route.
- Fusion combines light nuclei; it differs from fission of a heavy nucleus.
In the lab: Compare attributed stellar observations with predicted properties of each stage. Keep star, planet, galaxy and universe distinct. An orbiting body can have constant speed while its velocity changes direction.
Which two habits make the investigation or model in this case more defensible?
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- Known: in an illustrative sample, 8 of 40 observed stars are in a selected stage.
- Sample percentage = 8/40 × 100 = 20%.
- This descriptive fraction does not directly measure stage duration because observation and selection effects matter.
Your turn: 6 of 30 stars in an illustrative sample are in a chosen stage. Calculate the percentage.
6 of 30 stars in an illustrative sample are in a chosen stage. Calculate the percentage.
Độ khó 2/5 · 140 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
The result is 20 %. Known: 6 of 30 stars in the sample are in the chosen stage. Use percentage = count / total x 100. Percentage = 6/30 x 100 = 20%. This sample fraction does not directly give the stage's duration.
Check the conclusion and its limits
- The Sun is not expected to become a supernova.
- A diagram does not establish that every massive star makes the same remnant, nor that all stages last the same time.
Not true: The Sun is expected to end in a supernova. Only stars well above the Sun's mass end in supernovae. The Sun will pass through a red-giant stage and finish as a white dwarf cooling over time.
- A star forms from a collapsing cloud of gas and dust.
- Read a life-cycle diagram as a model of stages and conditions, not a timed film of one star.
- Watch for: the Sun is not expected to become a supernova.
Write from 25 percent of a sample
- 7 of 28 observed stars in an illustrative sample are in a chosen stage.
- Find the percentage. The Sun is not expected to end in a supernova.
The Sun is expected to end in a supernova.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
Only stars well above the Sun's mass end in supernovae. The Sun will pass through a red-giant stage and finish as a white dwarf cooling over time.
A stable stellar phase sustained by core hydrogen fusion: write the technical term.
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
main sequence means A stable stellar phase sustained by core hydrogen fusion.
7 of 28 observed stars in an illustrative sample are in a chosen stage. What percentage is that, and how is the Sun expected to end?
The sample percentage is the count divided by the sample size. Stellar end states depend on mass.
What percentage of this sample is in the chosen stage?
Độ khó 1/5 · 100 xu + một phần thưởng nhỏ cho lần hoàn thành đầu tiên trong ngày
7 divided by 28 is 25 percent. The worked 8 of 40 is 20 percent. Other options — 7 percent (the star count); 20 percent (the worked sample's percentage).