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we are looking at the last globular cluster in the Messier list Messier 107. there's a Trope on this channel that none of us likes okay clusters because they're all really boring so this is the last one m107 is actually if you want to find out this guy it's in the direction of the constellation of fucus which is famous for being the 13th constellation on the ecliptic which is the line that the Sun and all the objects in the solar system take through the sky famously it was left off of the zodiac signs because why would you want 13 zodiac signs and not a nice round 12 right rather than 13. so if you were born between the 29th of November and the 18th of December technically the sun was in officus and
not Sagittarius when you were born more evidence that astrology is falsifiable twaddle yes m107 is actually one of the objects that Messier left off the original list when it was published because it wasn't actually discovered until 1782 by messier's assistant Pierre Mission by that point you know the list was already accepted for publication and everything so it was left off Messier 107 was actually added along with Messier 105 and Messier 106 by Helen Sawyer Hogg in 1947. now Helen Sawyer hog is one of those like hidden figures of astronomy that none of us ever actually learned about in school or university but she was massively influential throughout her career in astronomy she published four
very big catalogs of globular clusters but there's another name attached to Messier 107 and that's Peter or staff Peter osterhoff was the co-head of the Leiden Observatory along with Jan ort so the ought cloud in the solar system is named after Jan ought because m107 is classed as an osterhoff type 1 globular cluster now there is a massive Trope in astronomy we classify everything into type one and type 2 and everything's supposed to fit neatly you know like think of supernova type one and type two you've even got like active Galactic nuclei that are powered by you know growing supermassive black holes but you see them from different angles so their classes type 1 and type two and then
you've got radio galaxies that you're going to emit radio light their clusters type one and type two as well you know those types were often decided back when there was a lot less data a lot less observations you know the sample sizes were much smaller our sample sizes grew as we got more and more data you realize obviously it's it's usually more of like a continuous distribution and you can't put some arbitrary threshold on it to make something into type 1 and type two so you know with the Supernova we end up with type 1A and type 1B which I won't see I've even heard people talk about active Galactic nuclei as well as like oh this is a type 1.8 just like it's it's just so ridiculous right in the case of uh osterhoff type 1
and type 2 globular clusters at first glance it seems to be that actually when it was decided they're obviously clear-cut but now we've got this larger distribution and perhaps there isn't but actually we'll get into that okay so I grabbed this paper from 1973 that talks about the definition that osthoff first decided on for these different globular clusters it's all based on actually um the variable Stars within the cluster what period do they pulse at essentially so in a type 1 cluster you have the Stars varying with a period of around about 13 hours and in a type 2 cluster you've got the Stars varying on a period of round about 16 hours so on first reading you think well that actually can't break
into a nice sort of dichotomy of two different types if it's just based on periods that's going to be a fairly large distribution and yeah if you look at this paper it's got figure two you can see they've got type 2 globular clusters here and type 1 globular clusters there and you can see actually there is sort of two peaks but still the distributions overlap a little bit but as people sort of investigated these type twos and type ones further one thing they realized but it was not just the periods that split the two things out they also found that there was a difference in how many heavy elements the Stars had in each of these clusters so we're talking things like yeah okay fine helium but also mostly things like
carbon oxygen nitrogen and obviously some of the traditionally more heavier Metals up to iron as well so the way that we find out if Stars contain those elements is we take a spectrum of the light from the Star and you splits it through a prism and you get this trace of the light and you see how much light of each wavelength or each color do we receive and sometimes we see that there are gaps these missing gaps essentially where you know there's a load of carbon in that star that's absorbing that particular wavelength because the electrons are essentially stealing it away to gain energy so type 1 osterhof Global clusters are classed as having slightly weak metal lines in the Spectra
of light from the globular cluster which is sort of the Spectra from all the stars in it and type 2 osterhof goblet clusters are classified as having very weak metal lines so essentially what that means is that the type twos have very little Metals in the Stars meaning the stars formed from Pure hydrogen gas in the universe whenever that goblet cluster formed whereas the type ones probably formed from less pure hydrogen gas hydrogen gas that had been polluted over the years by previous generations of stars that had lived and died there beforehand gone Supernova and thrown out these heavier elements into the universe so it looks as if they've got these two different metal contents then perhaps they formed at
different times or the other option is that they formed in different places out of different clumps of gas that then gave them these different properties as well so then in 2002 this paper came out and they were actually not looking at the type 1 osterhoff globular clusters like what Messier 107 was they were actually looking at some of the least metal Rich clusters so the type twos the ones that were probably formed from very pure hydrogen and they were looking at their orbits around the Milky Way so in the top left here essentially this is the flat plane of the Milky Way's disk essentially that's where all the stars are orbiting there so you're looking at it from The Edge on all the red dots are these Very Metal
poor globular clusters the type 2 osterhoff clusters and you can see they're all in this line above and below the plane of the Milky Way in whatever Direction you look at it from essentially you see them in that line and so what this paper said essentially was that all of these type 2 clusters seem to be lined up in like a plane like a flat plane in how they're orbiting the Milky Way like they're all orbiting with the sort of very similar properties which suggests they might all be coming from the same place like for example a satellite Galaxy that was in orbit around the Milky Way that's been torn apart by the gravity of the Milky Way and all the normal stars that was in that little Galaxy have probably ended
up you know just coalescing to become part of the Milky Way but the globular clusters which were you know held together by their own self-gravity probably stayed in this orbit and stayed you know looping around the very top of the Milky Way and looping Down and Under and Over And so that sort of settled the argument for a lot of people and said what the type ones have probably formed in the Milky Way itself a little bit later probably than the type 2 globular clusters that formed outside the Milky Way in a different galaxy and are now classes part of the Milky Way because the two have merged together and so it actually looks like these type 1 and type twos actually are separate distinct populations perhaps at
least anyway again it's you know sort of getting more data that hypothesis can change but that's the one people are sticking with for now which is quite rare for astronomy that you end up with type 1 and type 2 that are actually physically different uh in their properties as well so it means that Messier 107 you know is sort of an OG Milky Way Goblet of cluster and then it Formed you know in our own little backyard of the Milky Way then the question becomes do globular clusters similarly form within their own Dark Matter Halos so I found this paper called testing for dark matter in the outskirts of globular clusters so recall that dark matter is this elusive subject it's essentially you know how old is the universe this is roughly what the Hubble
time is but they assume that was
