Select the star life cycle that is accurate?
A. Star of one stellar mass, red giant, planetary nebula, white dwarf
B. Nebula, star of one stellar mass, supernova, black hole
C. Supernova, star of three stellar masses, red giant, nebula
D. Nebula, white dwarf, red giant, planetary nebula
The Correct Answer and Explanation is :
The correct answer is A. Star of one stellar mass, red giant, planetary nebula, white dwarf.
Explanation:
The life cycle of a star largely depends on its mass. Stars like our Sun, which have a mass of about one solar mass, go through a predictable life cycle that includes the following stages:
- Nebula: The star begins its life in a nebula, a large cloud of gas and dust. Under the influence of gravity, parts of the nebula collapse and condense, forming a protostar. As the protostar continues to contract, it eventually reaches a temperature and pressure high enough to start nuclear fusion, turning it into a main sequence star.
- Main Sequence Star: For most of its life, the star remains in the “main sequence” phase, where it fuses hydrogen into helium in its core. This stage can last billions of years.
- Red Giant: Once the hydrogen in the star’s core is exhausted, fusion slows down, and the core contracts while the outer layers expand. The star becomes a red giant, which is much larger and cooler than its previous state. In this phase, the star begins fusing heavier elements, like helium, carbon, and oxygen.
- Planetary Nebula: As the star sheds its outer layers, a glowing shell of ionized gas forms around the remaining core. This is known as a planetary nebula. The star’s outer layers are expelled into space, enriching the surrounding environment with heavier elements.
- White Dwarf: The remaining core, now mostly composed of carbon and oxygen, becomes a white dwarf. This dense, Earth-sized object slowly cools over billions of years. It no longer undergoes fusion reactions and gradually fades.
Why the other options are incorrect:
- B: Stars with a mass like the Sun do not undergo supernova explosions. Supernovae occur in more massive stars (at least three times the mass of the Sun).
- C: A star of three stellar masses would have a different life cycle, involving a supernova, not ending as a red giant.
- D: This sequence is incorrect because a white dwarf doesn’t become a red giant, and a nebula is not the result of a white dwarf.
In summary, the correct sequence for a low-mass star like the Sun is Nebula → Star of one stellar mass → Red Giant → Planetary Nebula → White Dwarf.