To determine the composition of the first star formed in the Milky Way's history, let's consider the conditions present in the early universe shortly after the Big Bang.
1. Primordial Nucleosynthesis:
- Right after the Big Bang, the universe primarily consisted of hydrogen, helium, and trace amounts of other light elements such as lithium.
- The process of primordial nucleosynthesis, which occurred within the first few minutes of the universe, led to the formation of these elements.
- The resulting elemental abundances were approximately 75% hydrogen, 25% helium, and less than 0.1% other elements.
2. Formation of the First Stars:
- The first stars, also known as Population III stars, formed from this primordial gas.
- Since no other heavy elements were created until the first stars began synthesizing them in their cores and dispersing them through supernovae, the composition of these earliest stars reflected the primordial abundances.
Hence, at the time of birth, we would expect the first star in the Milky Way to be composed of approximately 75% hydrogen, 25% helium, and less than 0.1% other elements.
Therefore, the correct answer is:
75% hydrogen, 25% helium, and less than 0.1% other elements.
