JWST's "too massive" galaxy problem solved?! | A non-universal IMF

so as we all hoped jwst has been giving us results that seem to contradict our best theory of how the universe works now us scientists all of it when something like this happens because we learn something new and the big sort of latest mystery that everyone's been puzzling over is the fact that in jwst data we've found galaxies that are too big they seem to have formed too many stars in too short of a Time quicker than what our best model of the universe says is possible now you might have seen some people online and in the media making claims that this means that the Big Bang never happened which is just plain wrong The Big Bang Theory describes the past 13.8 billion years of the universe's entire Evolution so making a statement like the big bang never happened just doesn't even make any sense while this result from jwst does mean is that their might be a problem or tension is is the word that scientists like to use to describe this with our best model of the universe Lambda CDM so Lambda here meaning that the universe is accelerating expanding and CDM stands for cold dark matter I there's dark matter in the universe we need it there to make all our observations make sense and it's called not hot now what that means is that Lambda CDM actually is is you know it's this it's the ratio of all of the stuff in the universe and how much of the universe's energy budget went to each of them but it's also this the hobble diagram showing that the universe is accelerating expanding but it's also this as well huge big cosmological simulations of the entire universe showing how galaxies first formed and evolved so it gives us things like you know a ratio of how much normal matter to Dark Matter there is in the universe and then that tells us okay well when Mata was first clumping together under Gravity to come together to form the first stars and galaxies how quickly could that happen how quick could it come together how did it come together and so therefore there was some Maximum density that you could actually have material at a certain point in the universe's history and so there was a maximum rate at which you could form stars now JD risk T allows us to see these processes happening for the first time to observe the first stars and galaxies it's it's a time machine and that cheese line gets thrown around a lot but it is essentially true right because light takes time to travel to us when we actually look at more and more distant galaxies we're seeing them as they were in the very early universe as we look further back in distance we're looking further back in time as well and this is how we are able to piece together this puzzle we can really only do this with Jade whiskey because the universe is expanding so light that's given out invisible wavelengths that we could see with our eyes and the likes of the Hubble Space Telescope is stretched so much by the expansion of space to longer and longer wavelengths into the infrared that it's beyond like the wavelength range that the whole Space Telescope can pick up and this is why we need jwst so one of the main goals for astronomers with JD boss T was to find the most distant galaxies they could and work out their properties now to do this essentially in images you look for the smallest reddest of objects that you can find and so once you've found them what you then do is fit models to the light that you record for these galaxies and those models can hopefully tell you something about the properties so you can do this in one of two ways either you can take a Spectra of a galaxy that's ideally what you would do so this is where you take the light from a Galaxy split it through a prism and you get a trace of how much lighter every single wavelength do you receive now that's a lot more complex than just taking images of something where you only let light through at certain wavelengths through a filter and so you can see how the two compare with the filters you essentially just get like the total brightness at this wavelength range but you miss a lot of the detail that gives you a lot more information then you're going to make a model essentially to say okay can I recreate this amount of light that I'm getting in these filters or can I recreate this trace of light in the Spectrum and from those models you can usually get out two main things one is the red shift and one is the Stellar Mass the amount of mass you have in stars now I've taught in videos before about how you actually get redshift from these observations which I'll link below if you're curious and want to know more but here in this video I just want to focus on how we estimate Stellar Mass from these observations with these fits so if you think it through right the brighter a galaxy is the more stars that are giving out that light the more stars there are the heavier Galaxy is so the higher the Stellar Mass except it's not that simple because you also need to know the amount of the different types of stars that you have in a galaxy because more massive stars are brighter and give off more light than less massive stars which are much fainter so if you're trying to account for like a given amount like a total amount of light from a Galaxy you could either say okay this light is coming from just a handful of very massive stars or you could attribute it to a huge amount of lower Mass Stars which cumulatively actually end up being heavier than just the few brighter higher mass stars the problem is we don't know how many of all of the different types of stars at different masses you actually tend to form in a very distant galaxy in the early universe that is not something that we can directly observe we can do it though for things much more nearby so for example in our own galaxy in the Milky Way we can actually see and count the individual different stars and find What's called the initial Mass function a distribution showing the spread of stars of different masses made in Star formation episodes across our own Galaxy so essentially the number of lower math stars formed compared add the number of higher mass stars formed and what's cool is that when we look at other galaxies nearby to us and look at you know how many stars of each different types of mass they form in these star formation episodes we find that these distributions are pretty similar they're very consistent with each other so if You observe a Galaxy and you say okay I know how bright this galaxy is and if I assume that it's forming the sort of same spread of the different types of masses of stars that I see in the Milky Way and you know how much light all those different types of stars give off then you can say okay I know how many stars must be in this galaxy therefore I can work out its Stellar Mass the problem is to do that you've made a really big assumption there you've assumed that the spread of stars this IMF the initial Mass function is going to be the same in that Galaxy as in the Milky Way we call this assumption a universal initial Mass function I the IMF is the same wherever you are in the universe it is universal but of course in reality probably not going to be the case you're going to have some variation in it like for example you could have more of the smaller Stars being formed in which case we call that a bottom heavy IMF or conversely you could be forming less of the smaller stars in which case you'd call that a bottom light IMF or you could be forming more of the heavier larger stars in which case that would be a top heavy IMF and then also you know if you're forming less of the larger Stars it's a top light IMF now there has been a lot of research in the past couple of decades trying to figure out if the initial Mass function is truly Universal or not or if there is some variation Beyond Randomness in different galaxies imfs and while we're pretty sure now that galaxies clearly do have different imfs there isn't a consensus yet on what we still should do and assume for different galaxies so the safe bet is still this Assumption of a universal IMF which is what a lot of codes or software packages that are written by astronomers and released for you know their fellow astronomers to use to do these fits to observations of galaxies in get out Stellar masses it's what a lot of those codes still assume a universal initial Mass function that's the same as the one that we observe in the Milky Way that's exactly what labor and collaborators did in their recent paper announcing the discovery of these very distant galaxies in the early universe and in it calculated their masses to be far larger than we ever would have expected but did so using this Universal IMF assuming it was the same as The Milky Way for these very distant galaxies in the early Universe boiling and culture then actually investigated these galaxies further finding that the most massive ones were in tension with Lambda CDM they are right on the edge of what is physically possible for these galaxies you know as we heard before at Lambda CDM given all the properties of the universe that we've measured tells us that there's only so quickly you can actually Clump material together in the early universe so at a given age in the universe's history there'll be this maximum density of normal matter sometimes called baryons in a Galaxy which in turn limits the density of stars that conform from that material so this blue region of the plot here is the part that's just physically impossible you'd have more stars than there is sort of normal matter available for them to form from and those galaxies that labian collaborates has found at about a redshift of nine they're right on the edge of what shouldn't be possible hence the statement that they're too big for our best model of the universe so yeah these results suggest that there could be something wrong with Lambda CDM which wouldn't surprise me there's a lot of things wrong in cosmology at the minute and a lot of that I've talked about on my channel before again I'll link some videos in the description if you're interested in a deeper dive into that and it could be that yeah we're missing some component of the universe we've measured something incorrectly that would change maybe the speed at which material was able to Clump together in the early universe and that would solve this and there's a lot of ideas sort of knocking around the astronomy community at the minute to come up with ways that perhaps you know this is why it's intention with Lambda CDM and I talked about this on my channel a few months ago when we first covered the fact that these Galaxies have been found in jwst data and I went through like all the possibilities for what could explain why their masses were so big like what could be wrong in terms of our assumptions but as you might have figured out already one way to resolve this might not be anything to do with lamb CDM at all it's this Assumption of a universal IMF the same IMF that you get in the Milky Way is you get in the very early universe that is completely different to the universe that we see around us today turns out that assumption is probably a bad one this is exactly what steinhart and collaborators have investigated so building on their work from you know the past few years looking at this Assumption of a universal IMF and if it's any good it turns out if you actually look at the temperature of the star-forming regions if the gas that's going to form those stars is actually hotter then you end up with a bottom light IMF producing less of the smaller stars now the early universe as we know was a hotter denser place than it is today so it's very likely that it's the star formation regions were also hotter and so there was a bottom light IMF in the early Universe the other thing to consider is the cosmic microwave background this relic of radiation that we get from the very early Universe today when we detect it it's microwave wavelengths of light with a very cold temperature of only around 2.7 Kelvin but that's because it's been redshifted by the expansion of the universe these lower energy wavelengths when it was first given out it was a much higher energy wavelength and it was much hotter so at Red shifts of like 9 10 11 12 and 15 these redshifts that now the jmst is actually pushing us out to the cosmic microwave background is still anywhere from let's say 40 to 60 Kelvin in temperature and so that kind of puts a limit on well the gas that's going to be forming your stars is also probably going to be around that temperature as well so what steinhardt and collaborators did was take the galaxies that lab and collaborators had found and re-fit them with a model that allowed the IMF to vary they find that when they do this the inferred Stellar masses drop because the IMF that they fit is bottom light at these higher redshifts there are less of these lower Mass stars but in big numbers actually do add up and give you more mass it's actually a really big effect the mass drop is sometimes you know over an order of magnitudes so what I mean by that is that these are logarithmic numbers so the actual sort of mass value is 10 to the power of the number given here in this table so a difference between 9 and 7.79 means there's over a 10 times difference in the seller mass and they once again looked at this baryon availability problem that boiling culture first looked at and found there was no longer an issue there's no longer any tension with Lambda CDM now that you've brought down this estimate of the mass of these galaxies at very high redshifts very early in the universe essentially they're not as big as we first thought the more accurate measurement of the mass has meant that the problem has just gone away just kind of sad because we haven't learned anything new about lumbed CDM but we have I guess learned something about the IMF and to be honest I wasn't surprised by this result I was kind of like yeah that checks out because for a long time we've known that this Assumption of a universal IMF is probably not a good one especially at high red shift in the very early Universe when conditions were very very different so on the one hand I'm like yeah makes total sense on the other hand I still have this sort of you know healthy dose of scientific skepticism over this because you could argue that what you've done is just added an extra parameter to your model so giving it more flexibility more degrees of freedom and so aren't you just overfitting the data now now the authors do address this concern themselves in the research paper and so suggest this two-pronged approach to combat this and so what you do once you've gone through all your images and found your galaxies that you think are going to be at high redshift the first fit you do is just with the standard normal Assumption of a universal IMF the same as the Milky Way and you do that fit and you get a redshift out to start with and then once you have that red shift you can be like okay well the cosmic microwave background at that redshift is going to be this temperature so that sets a limit on the temperature of my star-forming regions that are gonna be making stars and so it gives me an IMF straight out so a higher temperature you'll have a more bottom light IMF now you've then set your IMF in your next fit as a different one and you do the fit again to get out a redshift once more and a much more accurate estimate of the Stellar mass of the Galaxy that's what they're advising people to do in the future as they're getting their data from jwst which I think is a sensible way to go about it just to be aware that if you're trying to get at Mass like you can't just assume everything is going to be the same as The Milky Way now as always with this early jwst science that we've been seeing so much of for the past year this has just been done with images that the science team should get their hands on very quickly what you'd ideally want to do though to do these fits much more accurately is to get Spectra where you take the light split it through a prism and get that trace of how much light of each wavelength you detect it's so much more detailed so as always I feel like a broken record but we need more data and that are actually follow-up observations that are going to happen or maybe even already happened as well with jdbst where they're gonna get Spectra for these high redshift candidates that have been found in images and with that data you're going to be so much more detail we're going to be able to tell a lot more about the properties of these populations of stars in the very early universe as well like what they're made of that'll help inform the sort of models where fitting much better help constrain them a lot more and then that'll hopefully tell us you know what is the initial Mass function of galaxies in the very early universe before we get to the bloopers I just want to say a big thank you to brilliant for sponsoring this week's video brilliant.org is one of the best ways to learn science and maths interactively with thousands of lessons from foundational and advanced maths to AI to data science to neural networks and much more with new lessons added every single month if after watching this video you want to learn more about cosmology so that study of the evolution of the entire universe then check out this section of their fantastic astrophysics course which covers the basics of cosmological principles but also goes into a deeper dive on the temperature of the cosmic microwave background that we touched on in this video so to try everything that brilliant has to offer for free for 30 days head to brilliant.org forward slash Dr Becky or you can click on that link in the video description down below and the first 200 of you that go to that link are going to get 20 off and annual subscription so thank you so much to brilliant for sponsoring this video and now roll those bloopers I'm trying very hard not to angry cry right now because I just filmed this whole video it recorded without sound I don't know why I think my mic wasn't just plugged in right and it's just Friday afternoon I just worked on our best model of the universe Lambda shidia shedium it's shitty stars of different types and masses in its star formation episodes as The Milky Way very rude pip of a horn outside then I am in the middle of science yeah that checks out because for a long time we've known this Assumption of a universe Universal universe I sound like Goofy

Channel: Dr. Becky

Views: 549,701

Keywords: dr becky, astrophysics, physics, space, universe, scientist, astronomer, telescopes, james webb space telescope, hubble space telescope, aliens, NASA, ESA, becky smethurst, infrared, NIRCam, unfoldtheuniverse, cosmos, redshift, technology, JWST, absorption, NIRSpec, spectroscopy, galaxies, early universe, high redshift, lyman break, balmer break, stellar mass, star types, hydrogen, science, how we know, initial mass function, universal, IMF, density of stars, baryons

Id: W4KH1Jw6HBI

Length: 19min 37sec (1177 seconds)

Published: Thu May 04 2023

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[u/MarcusTheAnimal]

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