JWST spots the earliest galaxy to date

It’s been a big week for space science, with the imminent switch-on of a telescope that promises to scan the whole sky multiple times per week and may flush out planet X in the process, a new model that suggests we’re not on a collision course with the Andromeda galaxy after all, and scientists see farther back in time than ever before, documenting the earliest galaxy ever to exist, just 280 million years after the Big Bang. To take us through this cosmological hat trick is Matt Bothwell, author and “public astronomer” at the Institute of Astronomy in Cambridge. We kicked off talking about Mom z14, the catchy name they’ve given to this incredible galaxy born over 13.5 billion years ago…

Matt - It's a galaxy that we're seeing just 280 million years after the Big Bang, so it's the furthest back into the early universe we've ever been able to look before.

Chris - Why is that a breakthrough?

Matt - Well, the further away galaxies are, the harder they are to see for a couple of reasons. Firstly, just because seeing something more distant gets fainter. Also, the light gets stretched, gets what we call redshifted by the expanding universe, and so as the light from these really, really distant galaxies gets stretched, it disappears into the infrared, and then we need these special telescopes like James Webb to be able to see them. But also, because these galaxies are so brand new, they really are the first baby galaxies that ever formed in the universe, they're also just intrinsically really small, so that combination of small and far away and very, very red makes them very tricky to see.

Chris - The James Webb has done this. That also can look at the colours of the light that come, the spectra, which means we can tell something about the chemicals that are there. There's an interesting reference made to there being other elements like oxygen and nitrogen in those signals. Why is that significant?

Matt - Well, that's really exciting because these heavy elements have to be made inside stars, right? So the Big Bang itself only really made hydrogen and helium, and a tiny little sprinkling of lithium. Anything else, like oxygen, like nitrogen, like carbon, has to be made in the centres of stars, and then gets spread, seeded around the galaxies as the stars live and die. And the fact that we're seeing all these heavy elements in this galaxy only 300 million years after the Big Bang means there must have been multiple generations of stars living and dying and generating these elements, which means really that all the processes of star formation and galaxy formation in the early universe really kicked off a lot sooner than we thought it did. And I think the really exciting thing is what happens when you slightly pan out and realise this isn't just a one-off. What we're seeing here is evidence that there's a whole population of galaxies in the early universe, something like a hundred times more than we expected, which is just completely rewriting the story of how galaxies formed.

Chris - How does it change then our view of what the universe was doing in its infancy?

Matt - Well, it really adds to a story that James Webb has been telling since the first data came in, that just everything in the early universe was a lot brighter and a lot more vigorous and more populous than we first thought. The predictions were that there would be very, very little going on until about 500 million years after the Big Bang. And then we thought, starting from maybe 500 million years after the Big Bang, there'd be a few little sporadic galaxies around. But now we're seeing hundreds of millions of years before that, there are these stonkingly bright galaxies everywhere. And it just means there's a lot more to learn about how the first stars and galaxies formed.

Chris - So watch this space on that one. The other big story this week suggests, I'm not sure if I should be relieved or not, but we've been claiming for years that the Milky Way will end in a catastrophic cosmic collision because we're going to run into our next-door neighbour, the Andromeda galaxy. There's another paper now saying they've modelled this and they suggest this is very unlikely, something like a two to five per cent likelihood. What have they done and how did they arrive at that conclusion? Why did we get it wrong before?

Matt - Well, I think beforehand, people just did the pretty simple thing of looking at the Milky Way and looking at Andromeda and realised that we were moving towards each other at about 200 kilometres per second and then realised, well, you know, the natural thing is that we crash at some point. This new paper has done a lot more of a detailed dynamical model of all of the galaxies in the local group and not just looking at the Milky Way and Andromeda, but looking at a galaxy called M33, which is like this fluffy little spiral that hangs around the Milky Way and Andromeda, but also the Magellanic Clouds, these little dwarf galaxies that are orbiting around the Milky Way. And it turns out if you not only include the Milky Way and Andromeda, but all these little dwarf companions that are hanging around and you properly simulate the system, then it starts to look a lot more likely that the Milky Way and Andromeda are actually going to miss each other and then just orbit around each other for at least the next 10 billion years.

Chris - Do galaxies actually collide though? Have we got evidence of other galaxies having had a pile-up?

Matt - Yeah, absolutely. It happens really often. In fact, galaxies colliding together is one of the main drivers of star formation in the universe. One of my favourite objects in the sky is called the Antennae Galaxies and it was famously imaged by the Hubble Space Telescope. Listeners can go and look it up. It's the most beautiful picture. And it's two Milky Way-type galaxies that are in the middle of this titanic collision and all the gas and the dust is whirled together into this very sort of picturesque image. The Milky Way has had collisions in its past. We know that we have eaten several dwarf galaxies, but a big, what we call a major merger, like the type of thing that we'd see with the Milky Way and Andromeda where there are two big galaxies of comparable size crashing together, that is fairly rare.

Chris - What's the outcome of that? Or I could say, I suppose, the spin-off. Do you get things flung off into space? Do you get debris piling up or do they just merge into one bigger galaxy?

Matt - I think the end result is that they do just merge into one bigger galaxy. I think in the short term you get all kinds of really funky dynamical effects like you get tidal tails and structures and you presumably do get stars flung off into the intergalactic medium. But, you know, the ultimate end if you fast-forward a few billion years or so is that, yeah, the gravitational pull of the whole system will just smush everything together into one big galaxy that we used to call Milkdromeda but now might not actually happen.

Chris - Well, back down here on Earth there's also quite an exciting announcement that this observatory is going to go live, the Vera Rubin. What is that and why are scientists like you excited about its switch-on?

Matt - It's a brand new telescope which has this sort of three-mirror optical setup. The end result is that this telescope can do both wide-field imaging and get things in super sharp pinpoint detail. With telescopes we used to have to make a trade-off, but this telescope does everything, basically. And so what it's going to do is survey the entire sky every three days down to this unbelievable level of detail. So anything that's changing, anything that's moving in the sky, we're going to see it. It's going to be this incredibly detailed movie of the night sky for astronomers to study for years to come.

Chris - But haven't we already got the Gaia spacecraft? That's a space-based telescope that is taking lots of pictures of the sky like that. So how do the two projects differ?

Matt - So it is fairly similar. The advantage of the Rubin telescope is that it's much, much wider field. So Gaia does do what we call time-domain astronomy. It can look for things that are changing over time. But Rubin's just enormous field of view just means it does capture the entire sky a few times per week, which Gaia just has no hope of doing. So yeah, Rubin is like sort of Gaia on steroids, if you like.

Chris - And what will that enable us to do? Once you've got that time-lapse almost of how the night sky is evolving, what does that change about our ability to do astronomy, space science?

Matt - So there are all kinds of discoveries with Rubin that have been completely impossible before. It's going to find countless asteroids flying around the solar system, including things that might be dangerous to Earth that we can then take care of. If there is a Planet X in the outskirts of our solar system, Rubin will find it. And then going to the complete other end of the scale, it's going to make the biggest ever map of the universe. And that's going to tell us things about how dark energy and dark matter work on the biggest scales. It's a very exciting time.

Chris - When is switch-on?

Matt - 23rd of July is first light.