Are These Ancient Galaxies Too Big For Their Age?

8:17 minutes

Blurry photos of red and blue dots in space
A mosaic collected by James Webb of a region of space close to the Big Dipper, with insets showing the location of six new candidate galaxies from the dawn of the universe. Credits: NASA, ESA, CSA, I. Labbe (Swinburne University of Technology). Image processing: G. Brammer (Niels Bohr Institute’s Cosmic Dawn Center at the University of Copenhagen).

We’ve all been wowed by the amazing images from the James Webb Space Telescope, or JWST. But sometimes, the important data isn’t in those amazing galactic swirls or wispy nebula images, but in the images of tiny smudges from far, far away. 

Astronomers recently described some of those smudges, tiny red dots thought possibly to be ancient, distant galaxies, in the journal Nature. However, if the red dots do in fact represent galaxies, they appear to be too large to fit predictions for how fast galaxies form. The possible galaxies may be about 13 billion years old, forming just 500 to 700 million years after the Big Bang, but appear to contain as many stars as much more mature galaxies.

Dr Erica Nelson, an assistant professor of Astrophysics at the University of Colorado, Boulder and one of the authors of that paper, joins Ira to talk about the observation and what could explain the confusing finding.

Segment Guests

Erica Nelson

Dr. Erica Nelson is an assistant professor of Astrophysics at the University of Colorado, Boulder in Boulder, Colorado.

Segment Transcript

IRA FLATOW: Who hasn’t been wowed by the images coming out of the James Webb Space Telescope? But sometimes the important data is not in those amazing galactic swirls or those wispy nebula images. No, sometimes the important stuff is in the tiny smudges far, far away. Astronomers described their studies of some of these smudges as galaxies from the early, early universe, and they were surprised. Those galaxies should not be there, at least not at that size.

Joining me to discuss those mysterious masses is Dr. Erica Nelson, Assistant Professor of Astrophysics, University of Colorado in Boulder. and one of the researchers. Welcome to Science Friday.

ERICA NELSON: Hi. Thanks for having me.

IRA FLATOW: So how surprising was this?

ERICA NELSON: It was very surprising. This was definitely the most exciting discovery of my scientific career thus far. It was really amazing to see these things. We just did not expect them.

IRA FLATOW: Well, what did you expect to see?

ERICA NELSON: We expect to see really little, tiny galaxies when we look back to the very early universe. We don’t expect to see big behemoths like the Milky Way existing so close to the earliest cosmic times. There needs to be more time for those objects to form.

IRA FLATOW: Did you discover this by accident? Were you looking for something and found these?

ERICA NELSON: You know, I think the most exciting discoveries are definitely the ones you don’t expect. I was looking at these spectacular images when they were first released to us by NASA, and I noticed these bright red dots that were in the James Webb images that we didn’t see in the Hubble images. I was really struck by them.

And so my team and I started to try to figure out what these were, right? Because as astronomers, the only thing we get is light. And from that, we have to infer everything we would like to know about the objects we’re looking at. And it turns out these things were really massive galaxies that should not exist.

IRA FLATOW: Let’s talk about the science of how you knew all of this. How do you know how old they might be?

ERICA NELSON: The way we know their distance is by their redshift. So what that means is that as the light from an object is traveling through an expanding universe, its wavelength is stretched out by this expanding space that it’s traveling through. And when that light arrives at us, it’s gone from being light that we could have seen into the infrared. And so that’s how we know that these objects are really, really distant.

IRA FLATOW: Mm-hmm. And the surprising thing is that they’re too big for their age?

ERICA NELSON: Yes, that is exactly the surprising thing. The universe started we think in the Big Bang, 14 billion years ago. And at that point, all of space and time and matter and energy was created. And then it had to assemble itself into the structures that we see. And that started with the littlest things like atoms and then stars, and then eventually galaxies.

But we think because of that that galaxies, especially big galaxies, took a long time to build up, billions of years. And we see these galaxies. They’re really massive. They have the number of stars that the Milky Way has now at close to the beginning of cosmic time, and that just should not be possible.

IRA FLATOW: When you say close to the beginning, how close is that?

ERICA NELSON: 500 million years, which does not sound like a lot, but a lot had to happen before galaxies that big could form.

IRA FLATOW: So how fast are the galaxies supposed to form?

ERICA NELSON: We would expect objects like this not to be able to form for a couple billion years, and here they are at a couple hundred million.

IRA FLATOW: Wow. This is Science Friday from WNYC Studios. This brings up that age-old question. Do we have to rewrite the textbooks about how the universe formed?

ERICA NELSON: I mean, hopefully. But first, we are scientists, so we have to confirm that these galaxies are as big as we think they are. And then there’s a lot of other steps we need to go through before we say we have to scrap everything we think we know.

The universe as a whole dictates how the contents in it form, but there’s a lot of steps going from the big scale of the universe to the galaxies that we see. The dark matter forms scaffolding for all these galaxies, and then it attracts gas, and that gas has to form into stars, and those stars have to create galaxies. And so there’s a lot of different steps in that process that could be wrong before we say our whole model of the universe is wrong.

IRA FLATOW: How can you tell how big it is? I mean, if it looks just like a little red smudge, a dot, how do you know how many stars there are in it?

ERICA NELSON: That is a great question, and that is definitely the most challenging aspect of this work because you have to take light and turn it into a measurement of mass, which is a hard thing to do. And so we have these fairly sophisticated models for how you sum up the light from stars of different ages over the history of the object. And then from that, you can add up the total amount of mass that’s in those stars, and that’s how we infer the mass.

IRA FLATOW: Hmm. So where do you go from here? I mean, you’ve discovered something unexpected. What’s the next step in trying to prove that this is really real?

ERICA NELSON: We definitely need more detailed information. We need spectroscopy. So we really need additional data from James Webb in order to confirm that these things are what we think they are.

IRA FLATOW: Yeah. So there are other possibilities here? Maybe they’re not actually galaxies but some other kind of object?

ERICA NELSON: Yeah. The signatures that we see in their light are not like anything that we’ve ever seen before. So we think they’re massive galaxies, but it turns out one of them is already a supermassive black hole instead of a galaxy.


ERICA NELSON: Yeah. [LAUGHS] I know. Funsies. And we think of black holes as being dark, but if they’re eating, then they’re actually some of the most luminous objects in the universe. So one of these we think is a supermassive black hole, and others of them could be something even weirder.

IRA FLATOW: So this could actually open up a whole different kind of astronomy.

ERICA NELSON: I mean, that would be awesome.

IRA FLATOW: I mean, yeah, if it’s weirder, if you even really think about the formation, that’s kind of cool, isn’t it?

ERICA NELSON: Yeah. I mean, that’s why we launched this telescope, is to explore the wild, weird universe that we have out there and to discover completely new kinds of objects and things that we didn’t expect. If we launched this telescope and then it just confirmed everything that we thought we knew, that’d be so boring. But this way, the theorists will have work forever.

IRA FLATOW: Isn’t it more fun to find something you don’t know about than something you expect?

ERICA NELSON: It’s so much more fun, and that’s why I just did this by looking at the images and seeing what was there that I didn’t expect to see. And it’s cool because I was just flipping back and forth between these images, which is something anyone can do. I think one of the things that is a misunderstanding of astrophysics is that you have to be a math genius to make discoveries, but that’s not actually true. And I think it’s really important that kids know that in order to make discoveries about our universe, you just have to be curious about the world around you.

IRA FLATOW: And that’s a great way to end, Dr. Nelson, a great summary. And we’ll keep looking up with you.


IRA FLATOW: Dr. Erica Nelson, Assistant Professor of Astrophysics at the University of Colorado in Boulder.

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