The Chandrasekhar Mass for a Helium-Core White Dwarf
M_Ch(μ_e=2.0) = 1.4351 M⊙, identical to the carbon-oxygen value (1.4351 M⊙) because both compositions have exactly two nucleons per electron.
| Criterion | Points |
|---|---|
| Correct arithmetic | 12 |
| Correct identification of the identical mu_e values | 8 |
M_Ch(μ_e=2.2) = 1.1860 M⊙, smaller than the carbon-oxygen value (1.4351 M⊙), consistent with M_Ch ∝ μ_e⁻²: a larger μ_e produces a smaller limiting mass.
| Criterion | Points |
|---|---|
| Correct arithmetic | 8 |
| Correct direction consistent with the mu_e^-2 scaling | 7 |
1.018/1.4351 = 70.9%, identical (to the precision shown) to the 70.9% found in Lab 06, since the helium-core and carbon-oxygen Chandrasekhar masses are the same for this μ_e.
| Criterion | Points |
|---|---|
| Correct percentage arithmetic | 8 |
| Correct recognition that the two results are identical | 7 |
0.172/1.4351 = 12.0%, comfortably below the Chandrasekhar mass, consistent with its continued existence as a stable white dwarf.
| Criterion | Points |
|---|---|
| Correct percentage arithmetic | 12 |
| Correct stability conclusion | 8 |
Award full marks for correct method, units, and a numeric result consistent with the arithmetic shown (allow reasonable rounding). Verify that the student re-derives the number for this problem's specific inputs rather than quoting a lecture example without adaptation. Watch specifically for unit-conversion errors (km/AU/m, years/seconds, kg/M⊙) and for comparative-magnitude statements stated in the wrong direction (e.g., "X times greater" versus "a small fraction of") -- these are the most common sources of order-of-magnitude mistakes in this course.