nothing. You're looking at absolutely nothing. So, don't worry. You don't need new glasses. Yeah. So, this circle is showing where we've got some new observations from Hubble. Yeah. You're seeing absolutely nothing. And that's what they wanted to see because they were checking this location to see if they could see any stars at all. Uh, and they couldn't. There were no stars. So, well done them. It took a lot of my printer ink, though. And I did wonder whether it was worth doing. But there we go. But that's not nothing. There is something there. What's going on here? Why is this interesting to anyone? So, there's something there. Um, if you have radio eyes, so I'm a radio astronomer, which is why I get very

interested in this. And these were the optical observations from Hubble. But the radio observations from the very large array and the Greenbank telescope and the 500 spherical or awful 500 aperture spherical something fast in China huge radio dish. um were able to look at the same location first and they saw a cloud of neutral hydrogen gas or H1 gas. It's interesting to me because I just don't know what to call it and I don't think anyone does. And if you kind of look at what people are calling it on the internet, some people are saying it's a galaxy. It's a starless galaxy. Some people are saying it's a failed galaxy. Some people are saying it's a starless gas cloud. And I think that's

kind of where I land. So it just makes you think about what is it that makes a galaxy? What are the ingredients? And what happens when we're missing one of those ingredients? So, normally to make a galaxy, if I'm teaching this to students, I'll say, "Okay, you need gas. That's your building block. That's your building material. You need stars. That's what lights it up. And you also need dark matter. That's what keeps it together." Um, and you can see that dark matter indirectly by looking at the stars orbiting and seeing they're going way too fast. There has to be something holding them in. But this one, this one doesn't have any stars. It's got gas and we are almost certain it's got quite a

lot of dark matter. We can tell that because when we look at this gas, it's really dense in the core. It's a really nice dense core and it's not rotating, which means that it's kind of nothing's holding it up apart from its own apart from its own heat and nothing's holding it in. So, there has to be something there. Has to be dark matter. So, we've got two ingredients in this galaxy. Why does there have to be dark matter? What would happen if there wasn't? It would have been gone. it would have poofed away. And that's what will happen with a lot of different galaxies. So when we look at our simulations,

um when you're forming galaxies, galaxy formation, you form your dark matter scaffolding. You've got lots of kind of filaments. You've got nodes where you've got halos, lots of little halos, halos of dark matter. Then you get your gas coming in. That gas gets denser and denser. Then that ignites fusion and you get your stars. But what this has got is just this gas. And if it didn't have the dark matter, because it's been heated, it's been heated by all of the other stars in the universe, you've got a constant background of UV photons everywhere pinging. It's just keeping that temperature up. Um, so that gas is a little bit too hot. It should have just dissipated away. And many, many,

many, many billions will have. This one hasn't. So the gas is being penned in place, held in place by what? by dark matter by the so the gravity the gravitational potential we say of the dark matter. So this dark matter, you can think of it in spaceime. You've got a big clump of dark matter, a halo we call it. And how so is it a ring? Is it a is it? No, it's it's a bit of a misnomer. It's a sphere that um we're not even sure how that density changes with kind of from the middle to the edges, but we're pretty sure that it's kind of like, you know, everywhere really a big sphere of dark matter. So it's not like a fence around it. It's more like distributed.

No. And it's not even like a hard boundary. So when we measure um the stars that's really easy to see where andromeda ends for example it's really quite easy to see where the gas ends because the gas rotates as well and we can measure that with radio telescopes and it goes out probably sometimes double triple actually. So the if you look in the radio galaxies are way larger past that how do you really tell how far the dark matter halo goes? We don't ever really know. It's more like they probably all blend. Um, but yeah, so we know that something's holding this gas in this one. And so it's it's it's a really fun pristine laboratory actually for anybody interested in dark

matter because most of the time if you're interested in it and you're like, "Right, I'm going to use galaxies. I'm going to look at how the stars are moving." Oh my god, the stars are moving. They're mixing the gas like you've got merges from galaxies. It's a nightmare. It's like trying to do, I don't know, a really careful laboratory experiment on a fairground wala or something. Whereas this one, it's just chilled out. You've got nothing happening. Just dark matter and gas. You know, after all these years making these videos, I think today's the day I learned that these dark matter halos are not halo like in any way whatsoever.

They're kind of just like big clumps of Yeah, cuz there's dark matter in this room, right? I think it's it's just that I think the reason that we think of them as kind of this big fence on the outside is because they only start to we only really start to notice its effect on really large scales. So the dark matter in this room the density is so low that yeah I'm not suddenly pulled into a dark matter kind of gravitational potential but on a galactic scale then suddenly once you go past the stars then you've getting you're getting way bigger volume of dark matter and your stars have stopped. So suddenly it starts to dominate.

You referred to this possibly as like a failed galaxy. Should we assume that this could have become a galaxy and one vital thing didn't happen or are there millions of these things everywhere or what? Okay. So I think these are they're rare because they represent the turning point between two paradigms I suppose of galaxy evolution. Um, when we model the universe, we've worked out that there's a critical mass that your dark matter halo has to be to form a star forming galaxy. And that's because of various things. It's because of how hot the gases after the first stars have heated it, which something called realization.

Um, it's about the rotation of gravity. But that's around 10 to the 9.7 10 the 10 solar masses in terms of halo mass. Above that, you've got enough dark matter that even though your gases have been ionized, so that means your neutral hydrogen's turned into a um electron and a proton. Basically, even though that's happened, it can kind of calm down enough to come back together, star form. Lovely. It survives basically. Um below that critical mass, then what's happening is as we've already discussed, the gas just disappears and oh dear, you've got nothing to build with. that exact critical mass and actually this one which they're calling relic which is reionization limited H1 cloud

um uh in this one they think that the dark matter is about 10^ the 9 so almost exactly that critical mass so you're catching it you're catching this very small population that golds basically you know not too hot not too cold really tiny thing there's going to be loads of them out there rare relative to the those two different populations and they're also rare because they're really difficult to see because seeing well I mean they're really difficult to see. Okay, so even with radio telescopes seeing a diffuse faint cloud pretty tricky. I realize this has only just been found and not a whole lot's known, so maybe this is a silly question, but do we have any clues as to what the future of this thing might be?

Can it be tipped one way or the other? Can it diffuse or can it suddenly start collapsing down into stars or will it just be frozen here forever? So, this one is quite lucky because most of these relics we think will have been disturbed by um nearby galaxies. So, this one, for example, is in orbit around one called M94. There's another relic there that they haven't quite worked out whether the stars there or not. And mostly you'll have kind of seen pressure stripping. So just the fact that it's like almost like a gas wind coming off the main galaxy that would have stripped away the gas. There's a small hint that might be starting to happen here. In which case in the future, yes, it might be completely

stripped of its gas and it would just fail to exist anymore. It would just be a dark matter halo. And is that a galaxy? No, probably not. Um, but it's certainly not going to be the case that it could start to form stars. It would have to gather a huge amount more H1. There's just not much left in the modern universe to do that. We've used it all up. So, it is a failed frozen galaxy. Uh, yeah, from a long time ago, I guess. Tell me a little bit more about why this excited you. I know it all adds to the cannon of knowledge and we it's important to understand how galaxies form and this is a this just seems like a little aberration. And this is a sort

of a little one that falls between the cracks. Okay. So, firstly, I like any time that radio observations are able to kind of get one over on other wavelengths. I don't like to be too tribal, but um I do think it's it's just fun when that happens. I also really love it when Hubble still gets some air time after JWST is hogging everything. I love that Hubble's just being like, "Yeah, by the way, yeah, there's probably no stars there, and this is the first thing we've ever seen it, so cool." Yeah. It's still Hubble is still finding things that nothing we've never seen before. That's awesome. And then as a first stars astronomer, um I study the first stars, how they ionize that neutral hydrogen

and the first galaxies. And I think a lot about when does a group of stars become a galaxy? Because in the very early universe, you've just got a few first stars, maybe 10 of them together. Is that a galaxy? And actually, no, we don't think it is because there's kind of a fourth ingredient that I haven't mentioned in galaxies, and that is the ability to survive. So, you can have gas, you can have dark matter, you can have stars. But if when that first star goes into a supernova, which they do, very bright, very powerful. It blows all of the gas away, then you can't get a second generation. And that galaxy does fail at that point. And it has had a bit of star formation. for

example, that group of stars has failed to become a galaxy because it hasn't produced that second generation. Um, so that just interests me. This one has Oh, just in general. This one, no, this one hasn't. So, yeah, that's why I was pausing cuz I need to be very clear here. So, so in terms of like those first failed Well, there's a lot of failed those first clusters of first stars. And this is even I'm struggling because there's there's not really an official definition of a galaxy. So even I'm struggling, but people will say the first galaxies as if they're made of first stars. They can't exist because

they can't survive. This one shows no sign of having ever had any star formation. So there are plenty of galaxies out there called ultra faint dwarfs, which are even as small as 100 solar masses. Really faint, really small, not formed a star in forever. Those are kind of, you know, ones that have done a bit and then had a bit of a rest. Never going to do it again. Um, this one, yeah, just never got there. And that the things it's seen that interests me is that, you know, this kind of gas cloud, it would have been hanging around in the early universe and it's just survived. It's survived. Um, which is interesting. It's survived as a starless gas cloud. But the gas isn't like a primordial pure gas. It is the gas itself has

lived in other stars in the past. So this we're not completely sure of and this is why we need more um observations. But what we can be pretty secure as just from general knowledge of the field really is that this is a gas cloud that is in orbit around a major galaxy that has seen a lot of life. Um it's seen a lot of heavy elements being created in these stars. It's polluted its environment. So my gut feeling as a scientist in this area is that this cannot be pristine gas. Pristine gas is almost impossible to find and if you're going to find it, it's going to be an incredibly isolated places. This is not isolated. That's what also makes this quite interesting is it's in a busy neighborhood.

How big is it, by the way? Like compared to say like the Milky Way, is it a big thing or No, it's really compact. So I think it's about You'll have to look it up. I think it's about a 30th of the Milky Way. So I think it's around 1.4 kilopex whereas the um Milky Way is about 30 kilopex. So it's really compact and that's another thing that you look for in these relics because when you form them if you've got dark matter you've got gas. It's not rotating which by the way is another clue that there's not a really faint galaxy there. If I took my special spaceship and I flew there and I flew into the middle of it. So I parked in the middle. What would I see? Would I see out? Is it too

diffuse? Would I would it all be black? Could I survive? Would it be hot? Would it be, you know, would there be radiation? What would many questions? Um, you would see out. Um, if you survived, you would see out. Um, because neutral hydrogen, we can't see optically. So, you would if you there with your radio telescope or radio lenses or whatever. Um, then yeah, you would be surrounded by a fog. Um, but with my eyes, I would just I wouldn't even know I was in it. you wouldn't even know you were in it because you can't see dark matter, you can't see gas. Um whether there would be

kind of a radiation in terms of anything else. Neutral hydrogen, it only really does a few things and that's release photons of about 21 cmters in wavelength. Um and so yeah, you that's a really good question, but my gut feeling is that you could just sit there chilling out. You'd be very cold. You'd have a heater on. Yeah. But yeah, you would be cold. To find out more about what Emma's up to, including her research, her previous book, and her next book, check out the links down in the video description. Their movement laterally seems to us extraordinarily slow. So again, it's kind of like looking at a plane flying in a sky. You know, it's going at Oh god, Mal, you caught me. I don't know

how fast a plane goes. I'm going to say 300 mph. And you can write me. You know, if you had a car moving that fast in front of you, you'd be like, "We