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as you can see it's a globular cluster it's located in the constellation of sagittarius messier actually discovered this on the same night that he found m70 in this image which is taken by the hubble space telescope we're seeing a 3.5 arc minute field of view just for perspective the moon as seen from earth is about 30 arc minutes in diameter so this is about the tenth of the size of what the moon would look like so it's quite a small quite faint object especially in comparison to the other globular clusters in the messier catalogue it might be small and faint it is incredibly rich in metals are essentially any elements that are heavier than hydrogen or helium which are the most common elements in
our universe metals come about from stellar nucleosynthesis so this is when stars create heavier and heavier elements as they evolve over time they'll recycle these heavier and heavier elements back into the universe when for example they die via supernova explosions and they just expel all these elements back into the universe or through stellar winds to measure metallicity what we do is figure out how much iron there is in our object and so these can be measured through the spectral lines for example m69 has over 10 times more iron content than globular clusters of a similar age that might sound like a lot but it's not in comparison to stars that are young such as our sun so typically older stars that
formed in the very early universe when the universe only had really hydrogen and helium they would be more metal poor than comparison to some of the younger stars that formed like now to understand why this globular cluster is having more heavier elements than typical globally clusters of a similar age we can possibly explain it by looking at our galaxy so this is not our real galaxy the milky way obviously we can't look back on the milky way itself you can see it's a spiral galaxy but from edge on you can see that we don't live in a simple galaxy there's like different regions that make up a galaxy you first got a central bulge region that's quite dense and then you've got this flat disc like
region and you've also got this faint diffuse stellar halo and globular clusters are kind of all scattered about like this galaxy but they mostly live in the galactic halo unlike typical globular clusters m69 actually lives extremely close to the galactic center it essentially lives in the bulge of our galaxy so m69 i think is 6200 light years from the galactic center in comparison to our solar system which is like 25 000 light years away and so you can imagine that in the central regions it's more dense so you've got like a higher density of metals to kind of capture and you've also got a lot of type 2 supernova explosions from higher mass stars in comparison to the outskirts so that might be one of the reasons why m69
has such a high metallicity in comparison to other garbage clusters which you typically find in the halo or the outskirts of our galaxy and that is indeed what you see with other globular clusters that you find in the bulge region so studying globular clusters like m69 is really important then for understanding stellar evolution but also in understanding the bulge and the makeup of our galaxy itself even though the bulge of our galaxy is so important we still don't really know how it formed or when it formed for how it formed there are two scenarios one is through mergers so if you've got like satellites of stars etc you would expect through tidal friction and forces that eventually these would
accrete close to the center and create this bulge-like region the other scenario is that you have this disc and there's some sort of instability in the disc that creates this bulge but neither of these scenarios can explain why there are such old high metallicity stars at the center of our galaxy one of the ways that we can measure the age of m69 is by plotting the v magnitude of the stars in the globular cluster against the colour v minus i magnitude you get like this kind of finish shape in which we can fit theoretical models to and that tells us the age and we know now that m69 is about 14 giga years old that's pretty old and it's older than what we think our galaxy as a whole ages about 13.5
billion years old this points to the fact that the bulge which is where m69 lives must have formed quite early on and it must have gotten very high in metallicity very quickly they call it all through this atlas you'll find galaxies that it says oh yeah there's an ansay in this one or there isn't one in this one etc but nobody really knows why they're there how they form
