The stage where a contracting gas cloud begins to glow and contract, but fusion has not yet started.

The stage where a contracting gas cloud begins to glow and contract, but fusion has not yet started.

• A. Nebula
• B. Protostar
• C. Main Sequence
• D. White Dwarf

Answer: (B)

This question tests understanding of early star formation when a gas cloud contracts, glows from gravitational energy, and has not yet started fusion. As the cloud collapses under gravity, gravitational potential energy is converted into heat in the core, causing it to shine even though temperatures aren’t high enough for hydrogen fusion. This growing, luminous object is a protostar. It sits inside or near the original cloud and continues to accrete mass until core temperatures become sufficient for fusion. A nebula is the larger gas cloud itself and doesn’t necessarily describe the contracting, glow-producing stage of a forming star. The main sequence phase is when hydrogen fusion begins and sustains the star’s light, so it’s after fusion starts. A white dwarf is a later remnant—what a star becomes after its evolution ends, not during its initial glow from contraction.

This question tests understanding of early star formation when a gas cloud contracts, glows from gravitational energy, and has not yet started fusion. As the cloud collapses under gravity, gravitational potential energy is converted into heat in the core, causing it to shine even though temperatures aren’t high enough for hydrogen fusion. This growing, luminous object is a protostar. It sits inside or near the original cloud and continues to accrete mass until core temperatures become sufficient for fusion.

A nebula is the larger gas cloud itself and doesn’t necessarily describe the contracting, glow-producing stage of a forming star. The main sequence phase is when hydrogen fusion begins and sustains the star’s light, so it’s after fusion starts. A white dwarf is a later remnant—what a star becomes after its evolution ends, not during its initial glow from contraction.