Ask Ethan: Why Were The First Stars Much Larger Than Even Today's Biggest Ones?

[Judi Lynn]

Aug 25, 2018, 10:00am

Starts With A Bang
Ethan Siegel Contributor
Starts With A Bang




Place enough mass together in one place, give gravity enough time to contract and collapse it, and you'll eventually get a star. Get a large enough cloud of matter together, and you'll get a huge cluster of new stars, with a wide variety of masses, colors, and temperatures to them. Yet, if we look to the earliest times, we fully expect to find that the most massive stars from back then were far larger and heavier than any we find today. Why is that? Steve Harvey wants to know, asking:

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.

It's a tough pill to swallow, because the only thing that's changed appreciably, from then until now, is the elements that make up these stars.

If we look at a star like our Sun, we can find evidence for a whole slew of elements that span the periodic table. In the outer layers of a star, you can see what elements are present by their absorption features. When electrons, in atoms, see a slew of incoming photons, they can only interact with the ones that have a specific amount of energy, corresponding to the energy levels that cause atomic transitions for that particular element. In the Sun, alone, there are scores of elements.

More:
https://www.forbes.com/sites/startswithabang/2018/08/25/ask-ethan-why-were-the-first-stars-much-larger-than-even-todays-biggest-ones/#3f75ba6e9dee