Which statement describes a protostar?

Which statement describes a protostar?

• A. A matured main-sequence star
• B. A young star in early formation
• C. A dying star
• D. A star with planets

Answer: (B)

A protostar is a young star in the early stages of formation. It forms when a dense region of a molecular cloud collapses under gravity, heating as it contracts. The energy mainly comes from gravitational contraction, and hydrogen fusion hasn’t started yet, so it’s not a fully formed, stable star. Protostars are often surrounded by an accretion disk and envelope of gas and dust, and they shine mainly from the heat of collapse rather than sustained nuclear fusion. As the core becomes hot enough for fusion, it will settle onto the main sequence. The other descriptions describe later stages or different features (a mature main-sequence star is already fusing hydrogen, a dying star is in late-stage evolution, and having planets isn’t what defines a protostar).

A protostar is a young star in the early stages of formation. It forms when a dense region of a molecular cloud collapses under gravity, heating as it contracts. The energy mainly comes from gravitational contraction, and hydrogen fusion hasn’t started yet, so it’s not a fully formed, stable star. Protostars are often surrounded by an accretion disk and envelope of gas and dust, and they shine mainly from the heat of collapse rather than sustained nuclear fusion. As the core becomes hot enough for fusion, it will settle onto the main sequence. The other descriptions describe later stages or different features (a mature main-sequence star is already fusing hydrogen, a dying star is in late-stage evolution, and having planets isn’t what defines a protostar).