A really, really ancient star

SMSS J031300.36-670839.3 is possibly one of the oldest stars ever identified. We don't know it's age, writes Invader Xan at the Supernova Condensate blog. But, based on the colors of light it produces, there's reason to think it dates to a time that is damn near impossible to comprehend.

To find a star which is so devoid of metals, it must be old. Very old. In fact, the venerable SMSS J031300.36-670839.3 shows all the hallmarks of being one of the second generation of stars ever formed. The first ever stars formed quite soon after the Universe was born. They were composed of little more than hydrogen and helium. As a result, they were massive, fast burning, and rapidly died as supernovae. Known as “Population III” stars, these mysterious primordial stellar beasts have never actually been observed. However, we know they must have existed.

You can read more about the star at the Supernova Condensate blog. And be sure to check out the comments where there's an answer to the question, "If this star is so old, why isn't it dead yet?"

Notable Replies

  1. If stars shine through fusion, making heavier atoms from lighter ones, surely a star of any age tends to having heavier atoms over time rather than lighter. I don't understand the science in this story. Can someone explain how such an old star can have so few heavy atoms in its spectrum?

  2. Little stars last the longest but only fuse hydrogen up to helium, so don't really produce heavier elements. Those are formed in the later stages of larger stars - and to simplify some, even there you tend not to see so much, since the layers aren't mixed as well and so the heaviest elements remain around the core while it lasts.

    Combining the two, when you see lots of truly heavier atoms in the atmosphere of a star, you can conclude they were mostly already in the mix of gases that it formed from. So a star with none is one that ought to have formed before such elements started being released.

  3. miasm says:

    I haven't even finished the article yet and my jaw is already on the floor.

    Just 6000 light years away

    Ok, so it's not light from ages ago at the edge of the visible universe. It is only 6000 light years away and isn't moving near the speed of light through the galaxy. It is not composed of heavy metallic elements but is noted as being a second generation star, not too cold, 0.8 solar masses...

    It can't be that old.

    My money is on some kind of new star forming mechanism which somehow strips out metal or light elements to form a star... I mean, what the hell has it been burning otherwise?

  4. Stars even a little smaller than the sun are expected to last a lot longer. That's partly because the brightness falls off quickly, but also because in the sun only the outer layers are cool enough to convect, so only the hydrogen around the core is available to sustain fusion. As stars get smaller, though, more and more of the gas is mixed together and so available as fuel. I think models give a 0.8 solar mass star as lasting maybe 20 billion years; a 0.2 solar mass star should last trillions.

    So actually, a question about population III stars is why there aren't lots of them still floating around. An explanation I had heard is that they probably only formed much larger; elements like carbon act like catalysts for hydrogen fusion, so before them proto-stars maybe took longer to ignite and thus tended to accumulate more mass first.

  5. It's the Excession, of course.

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