What two elements dominate the bulk mass of any stellar nebula, forming material or dispersing remnants?
Answer
Hydrogen and Helium
The fundamental composition of any stellar nebula, regardless of whether it is actively forming stars or dispersing after a stellar death, is overwhelmingly defined by the two lightest elements, hydrogen (H) and helium (He). These components constitute the vast majority of the mass present in the initial interstellar medium and also in the expanding shells expelled by dying stars, such as planetary nebulae. The concentration is extremely high, with hydrogen often accounting for roughly ninety percent of the mass, and helium making up most of the remaining portion. This specific ratio reflects the universe's initial composition established shortly after the Big Bang.
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