3 ms·

Is there an explanation anywhere for how it's even possible for this type of star to live this long?

by dak1 14y ago

btilly 14y ago
http://en.wikipedia.org/wiki/Stellar_evolution#Low-mass_stars http://en.wikipedia.org/wiki/Stellar_evolution#Low-mass_star... explains that stars below half a solar mass never manage to burn helium, and can stay burning hydrogen for longer than the universe has existed. Stars below 0.1 solar masses are estimated to keep burning for trillions of year.
andrewcooke 14y ago
i think you're misunderstanding slightly why this is important. it's not surprising for small stars to live a long time (they burn quite slowly). what's surprising is that we don't see any older than about 14 billion years old. so that suggests that the universe is only that old. and really, to astronomers, that's not surprising either, since the universe is known to be that old from other measurements. what's actually surprising is that this star matches the universe's age so closely when it contains some elements other than hydrogen or helium. since that implies that it wasn't one of the first stars made (which would be pure hydrogen and helium), but a star made from remnants of other stars. so it is at least "second generation". so there must have been some stars of short lifetime before it. and it's actually tricky to fit that in, given how we think stars are created and how the universe evolved (the real problem is that the hydrogen starts out fairly evenly spread out and needs time to clump, under gravitation, to form the first stars - the density fluctuations that describe this are constrained by observations of the microwave background, which is quite smooth). [some more background to make this consistent: the universe "started" as hydrogen; large stars, which live a short time, can make other elements than helium from hydrogen; small stars, which live a long time, make only helium from hydrogen.]
- gus_massa 14y ago
  I think that your explanation is essentially correct. But most of the Helium was formed during the 20 minutes after the Big Bang, not in the stars: http://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis http://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis
  - andrewcooke 14y ago
    oh, you're right. sorry, i will fix that. oh, no i won't - the edit window has expired. how embarrassing.
    - gus_massa 14y ago
      It's not embarrassing. I learned it only a few years ago and I was very surprised. And looking for more information, today I learned that the Milky Way is a barred spiral galaxy. When I was young the Big Bang only produced Hydrogen and the Milky Way had no bars :) . http://xkcd.com/1053/ http://xkcd.com/1053/
      - andrewcooke 14y ago
        well, it's more embarrassing when you know i've made observations that measured the amount of that helium... :o(

Is there an explanation anywhere for how it's even possible for this type of star to live this long?

by dak1 14y ago

Is there an explanation anywhere for how it's even possible for this type of star to live this long?

http://en.wikipedia.org/wiki/Stellar_evolution#Low-mass_stars http://en.wikipedia.org/wiki/Stellar_evolution#Low-mass_star... explains that stars below half a solar mass never manage to burn helium, and can stay burning hydrogen for longer than the universe has existed. Stars below 0.1 solar masses are estimated to keep burning for trillions of year.

andrewcooke 14y ago

i think you're misunderstanding slightly why this is important. it's not surprising for small stars to live a long time (they burn quite slowly). what's surprising is that we don't see any older than about 14 billion years old. so that suggests that the universe is only that old. and really, to astronomers, that's not surprising either, since the universe is known to be that old from other measurements. what's actually surprising is that this star matches the universe's age so closely when it contains some elements other than hydrogen or helium. since that implies that it wasn't one of the first stars made (which would be pure hydrogen and helium), but a star made from remnants of other stars. so it is at least "second generation". so there must have been some stars of short lifetime before it. and it's actually tricky to fit that in, given how we think stars are created and how the universe evolved (the real problem is that the hydrogen starts out fairly evenly spread out and needs time to clump, under gravitation, to form the first stars - the density fluctuations that describe this are constrained by observations of the microwave background, which is quite smooth). [some more background to make this consistent: the universe "started" as hydrogen; large stars, which live a short time, can make other elements than helium from hydrogen; small stars, which live a long time, make only helium from hydrogen.]

gus_massa 14y ago
I think that your explanation is essentially correct. But most of the Helium was formed during the 20 minutes after the Big Bang, not in the stars: http://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis http://en.wikipedia.org/wiki/Big_Bang_nucleosynthesis
- andrewcooke 14y ago
  oh, you're right. sorry, i will fix that. oh, no i won't - the edit window has expired. how embarrassing.
  - gus_massa 14y ago
    It's not embarrassing. I learned it only a few years ago and I was very surprised. And looking for more information, today I learned that the Milky Way is a barred spiral galaxy. When I was young the Big Bang only produced Hydrogen and the Milky Way had no bars :) . http://xkcd.com/1053/ http://xkcd.com/1053/
    - andrewcooke 14y ago
      well, it's more embarrassing when you know i've made observations that measured the amount of that helium... :o(