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what we got today all right we've got messier 5 today or ngc 5904 here it is as you see it's a massive globular cluster that's nice it's absolutely full of stars there's about a hundred thousand to five hundred thousand stars in the scorpio cluster alone it's about 13 billion years old so we're talking right near the start of the universe this has been around four it's also 165 light years across which is massive so if you think about the milky way itself is about 100 000 light years across and this is 165 so i worked out it's about 0.1 of a percent of the entire milky way which considering this is just one object like is huge right like it's massive so the good thing that about the fact that it's so big is it has a lot of rare
stars in it as well so it has about a hundred what's called rr lyrae stars which are super variable stars and they are variable very regular their period of variability is related to their luminosity so you can use them to measure distance which is what i was going to talk about until i found a paper talking about this that uses m5 as a particle physics laboratory yeah i was like what these crazy particle physicists doing now what's this is the paper here yeah this is the paper so particle physics constraints from the globular cluster m5 so they are trying to measure this neutrino dipole moment it's a magnetic dipole moment neutrinos form as part of the standard model of particle physics this idea that you know they know all
the particles and this is the model that you have okay so protons electrons quarks all this stuff neutrinos okay neutrinos are absolutely tiny like the tiniest mass they're about a million times smaller than an electron okay so we're talking incredibly small the only reason that we even knew they existed was because in radioactive decay reactions sort of if you balance the two sides of the equation about what you started with and what you decayed into it wasn't quite balanced right it was always a tiny amount of energy that was sort of missing on the decay side and people thought you know it could be an error in the calculations until they realize actually it's another particle it's just absolutely tiny so
this happens in the sun where you get these radioactive decays into neutrinos and so the sun is producing a ridiculous amount of neutrinos all the time so if i just hold my thumb up 65 million neutrinos just pass through my thumb oh are you okay yeah well there's the thing they don't interact at all so what do they mean by magnetic dipole okay so a magnetic dipole is basically just a bar magnet you know you have something with a north end and a south end thing is particles can also be magnetic dipoles so despite the fact that say an electron or a neutrino doesn't really have north and south poles like a bar magnet does because it has this weird quantum property called spin because it has charge it also has a magnetic dipole the moment basically
means the force that if you put that magnetic dipole in another magnetic field the force that particle would feel in that magnetic field so what they're basically trying to do is measure what's the magnetic dipole moment of the neutrinos by seeing how they behave in the magnetic field of the stars in the globular cluster of m5 what happens is in stellar lifetimes okay you have normal stars that just happily burn hydrogen all the time on what we call the main sequence you know they've sort of related their color and their brightness and this sort of really tight sequence when they start to run out of the hydrogen okay they become what's called a red giant okay so they swell to this huge big size and get very bright
and in their core they're not burning hydrogen anymore because you've just been left with all the helium that's been left over but they are still burning it in this sort of tiny plasma shell around the core still energy can't really escape from that shell because it's a plasma but what starts to happen is that because you've got all this plasma there you start to turn photons to light into neutrinos so you basically get this decay that happens photon into neutrino and antineutrino and because they barely react with anything they can escape and you get energy loss okay and that allows the star to stop the temperature and the pressure getting bigger and bigger until basically you ignite helium burning okay
and when that happens you dim again and you move away from being a red giant so basically producing all these neutrinos allows the star to stay brighter for longer and on this red giant branch if we think about what this might look like this is a colour magnitude diagram you might have seen this before in other messier object videos we like to draw these a lot like about 100 times yeah so this is your color and this is your magnitude or your brightness here's the sort of main sequence where stars sort of live most of their life you have very dim things up here and very blue things that are very bright up here okay and these are more massive as well then when things start to turn into red giants they move off
onto this sort of branch over here until they reach the brightest tip that they can before that helium burning kicks in and they move off it again and that's rather exaggerated but basically what they're looking for is how bright this red giant tip can get here this is the red giant branch rgb okay then how bright is this tip what this depends on is how much energy you can lose in neutrinos why can't you just do this with every star in the universe so because the messier object m5 is this globular cluster all the stars have been formed at the same time and they all have the same age so when you plot this colour magnitude diagram you know how old the stars are because all of them have started to turn off
onto the red giant branch of a certain age so if these are the young ones i've got from here and these have all turned off and i've still got all my old stars down here if i get an older population of stars then this red giant branch will actually be down here because all of these have already died and only these ones are now on the red giant branch and so what you end up with if you get all the stars milky way you just end up with this big smear of red giant branches okay and so this depends also on how many metals were in the gas that formed the stars in the first place as well so many different variables what you need is something that's all of the same age and same properties to be able to give you that very precise like
tip of the red giant branch so do you want to see the plot of their colour magnitude diagram that they made in the paper yeah don't go on all right so mine was a little bit exaggerated and theirs is a really old population as well the red giant branch isn't as clear so this is your magnitude again and this is your color okay and on this side here is your main sequence okay and then this is your red giant branch coming off and coming up here and then this is where they've swept off to do helium burning and gotten a little bit cooler this right here this is your red giant branch tip and this is the thing that they were trying to find and trying to get a really precise location for that so it's the same thing as they
were there and so once they'd found that they then applied all their models of stellar theory to say okay well how long has it taken them to get there and how much energy loss would you have to have from the neutrinos and therefore how are those neutrinos behaving in that magnetic field and they derived a value for this dipole moment of 2.6 times 10 to the minus 12 of an electron's magnetic dipole moment well i can sleep easily tonight you can definitely sleep easy now no now that we all know that but the fact that you can get that number from a globular cluster in our milky way you know something that is 24 000 light years away you can measure something of the tiniest particle known is pretty
cool and it cost them nothing to build like the large hadron collider yeah exactly they didn't need some massive particle accelerator to figure this out they managed to do it with good old-fashioned astronomy can you tell me about this i don't even know where to start you just have to start talking because i'm so excited this specimen um we believe came to the museum in 1910 it was a gift from the royal society of tasmania
