Where does a 1-solar-mass protostar appear on an H-R diagram?
A) to the right of the main sequence, and lower down than the Sun
B) to the right of the main sequence, and higher up than the Sun
C) to the left of the main sequence, and higher up than the Sun
D) Nowhere—only stars that have fusion in their cores can be shown on H-R diagrams.
The Correct Answer and Explanation is :
The correct answer is B) to the right of the main sequence, and higher up than the Sun.
Explanation:
An H-R (Hertzsprung-Russell) diagram is a scatter plot of stars, with the temperature of stars (often represented by their spectral class) plotted on the horizontal axis and their luminosity or absolute magnitude on the vertical axis. This diagram is crucial for understanding the stages of stellar evolution.
A 1-solar-mass protostar is in the early stages of its evolution, before it begins nuclear fusion in its core. During the protostar phase, the star is still contracting and heating up, but it is not yet a fully-fledged main-sequence star.
Here’s why B) to the right of the main sequence, and higher up than the Sun is the correct answer:
- Protostar Location:
Protostars are typically found to the right of the main sequence on the H-R diagram. This is because they are cooler than main-sequence stars (especially compared to their more evolved counterparts) and radiate much more energy due to the contraction of their gas, despite not having fusion occurring in their cores yet. This gives them a lower surface temperature (right on the diagram) but relatively higher luminosity (higher on the vertical axis). - Comparison with the Sun:
A 1-solar-mass protostar will be more luminous than the Sun during its formation. This is due to its gravitational contraction, which results in the release of energy before fusion starts. As the star heats up, it radiates more power than it will when it is on the main sequence. - Main Sequence:
Once fusion begins in the core, the star stabilizes and moves onto the main sequence, where it will remain for the majority of its lifetime, depending on its mass.
Therefore, a 1-solar-mass protostar appears to the right of the main sequence and higher up than the Sun because it is cooler than a main-sequence star of the same mass but significantly more luminous due to the energy from gravitational contraction.