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What particularly surprises me about this is that the star is in our own galaxy. I'm used to the idea of seeing remnants from the early universe from observatio

by simonh 5y ago

What particularly surprises me about this is that the star is in our own galaxy. I'm used to the idea of seeing remnants from the early universe from observations of very distant galaxies, but of course then we're seeing them as they were long ago. This is a second generation star that's almost as old as the universe, but in our neighbourhood and we're seeing it as it is "now" (or close enough). I wonder where in the galaxy it's located? Intuitively I'd expect such an object to survive longer if it were out in the rim or halo of the galaxy, in a more rarified region, but of course intuition on these things can be very misleading.

astro123 5y ago
Small stars live a very long time. A star of the mass of our sun has a lifespan of ~10 billion years which gets you almost back to the beginning of the universe (~13 billion). This star is smaller (0.8 solar masses), so it can live even longer, so we don't need to look at distant objects to see early, low mass stars. The other issue is that we just can't see individual stars at cosmological distances except in incredibly rare cases. See for example [1] where they discovered a single star at redshift 1 (roughly 6 billion years ago). Basically, if the star gets lensed in just the right way, it can be hugely magnified. This is a strong contender for the coolest observation that I know about. Galaxies are hard to see at redshift 1, to get a single star is crazy. On your second question, generally people think that galaxies formed "inside-out". I.e. the inner region forms first, then the outer region. See [2]. Stars almost never collide with things (except maybe at the very center of the galaxy, but still super rare there), so survival isn't really a function of position in the galaxy. That said, this observation is in stripe 82 (a very famous section of the SDSS. They observed it to greater depth than the rest of their area and many other surveys have since also observed it) which I'm pretty sure is away from the galactic plane (so not straight toward the center). [1] https://iopscience.iop.org/article/10.3847/1538-4357/ab2888 https://iopscience.iop.org/article/10.3847/1538-4357/ab2888 [2] https://www.nasa.gov/mission_pages/WISE/multimedia/pia17554.html https://www.nasa.gov/mission_pages/WISE/multimedia/pia17554....

by simonh 5y ago

astro123 5y ago

Small stars live a very long time. A star of the mass of our sun has a lifespan of ~10 billion years which gets you almost back to the beginning of the universe (~13 billion). This star is smaller (0.8 solar masses), so it can live even longer, so we don't need to look at distant objects to see early, low mass stars. The other issue is that we just can't see individual stars at cosmological distances except in incredibly rare cases. See for example [1] where they discovered a single star at redshift 1 (roughly 6 billion years ago). Basically, if the star gets lensed in just the right way, it can be hugely magnified. This is a strong contender for the coolest observation that I know about. Galaxies are hard to see at redshift 1, to get a single star is crazy. On your second question, generally people think that galaxies formed "inside-out". I.e. the inner region forms first, then the outer region. See [2]. Stars almost never collide with things (except maybe at the very center of the galaxy, but still super rare there), so survival isn't really a function of position in the galaxy. That said, this observation is in stripe 82 (a very famous section of the SDSS. They observed it to greater depth than the rest of their area and many other surveys have since also observed it) which I'm pretty sure is away from the galactic plane (so not straight toward the center). [1] https://iopscience.iop.org/article/10.3847/1538-4357/ab2888 https://iopscience.iop.org/article/10.3847/1538-4357/ab2888 [2] https://www.nasa.gov/mission_pages/WISE/multimedia/pia17554.html https://www.nasa.gov/mission_pages/WISE/multimedia/pia17554....