Ask Ethan: Why Were The First Stars Much Larger Than Even Today’s Biggest Ones?
“I do not understand why a star’s metallicity has an impact on its size. Why? I am asking this because in one of your articles, you were saying that in the beginning of the universe, stars with mass almost 1000 [times] the sun’s mass probably existed because they were almost 100% hydrogen and helium.”
There’s a bit of a puzzle in the Universe: the stars we form today are about 40% the mass of the Sun, on average, and the most massive one we’ve ever discovered is about 260 times the mass of our Sun. In the very early Universe, however, before any other, prior generations of stars formed, we expect the average stellar mass will be 10 times the Sun’s mass, with the largest stars reaching upwards of 1000 solar masses. If the only difference is the amount of heavy elements, then why, if metals help with cooling and enable stars to form more easily, would the first stars be biased towards higher masses?