Astronomers Were Not Expecting This
Newly discovered galaxies are scrambling our story of the universe.
Humans have long found meaning in the stars, but only recently have we begun to understand whole clusters of them—galaxies, way out in the depths of space. A few nearby galaxies, such as Andromeda, have always been visible to the naked eye as a dusky smear in the night sky. Other shimmery structures became known to us after the invention of the telescope in the 17th century, along with a debate about their nature: Were they clouds of cosmic dust within our Milky Way, or “island universes” of their own?
Not until the 1920s did humanity identify these glowing clouds as galaxies, when the astronomer Edwin Hubble (relying on the work of a lesser known astronomer, Henrietta Leavitt) found that some stars were too far away to belong to the Milky Way. And only in the mid-1990s, when a space telescope named for Hubble peeked farther into the universe than ever before, did we find the thousands of galaxies shimmering across the universe—island after island in a vast cosmic sea.
After Hubble, astronomers felt pretty confident that they understood galaxies and how nature makes them. But some new, startling developments have recently popped up, courtesy of a space telescope far more powerful than Hubble. The James Webb Space Telescope, in full operation since last summer, has shown that galaxies formed much sooner after the Big Bang than scientists previously thought—and that some of them are unexpectedly large, absolutely brimming with stars. The findings have thrown scientists into a new reality in which their existing theories no longer apply.
Everyone in the astronomy community knew that the Webb telescope was going to be revolutionary. “And we had a very clear list of things that we thought Webb would totally blow our socks off about,” Joel Leja, an astronomer at Penn State University, told me. But the discovery of cosmically chunky galaxies where there shouldn’t be any? “This was nowhere on it. No one was looking for this.”
Instruments like Hubble and Webb are something like time machines. When the observatories look out into the depths, they’re basking in starlight that left its source eons ago, and has been traveling across the universe toward us ever since; in other words, to understand the cosmic beginning, astronomers must look for the most distant galaxies. Before Webb, scientists believed that those early, distant galaxies emerged at a leisurely pace. The first stars formed when clouds of hydrogen gas collapsed in on themselves and ignited. Then gravity drew the ancient orbs together into galaxies.
All of this drawing together of disparate matter into massive cosmic neighborhoods was assumed to have taken at least 1 billion years. Sure, the most distant galaxy that Hubble ever spotted was unexpectedly bright for the cosmic conditions of the time, indicating a larger collection of stars than should have been possible. But astronomers didn’t think too much of it then. They expected that Webb, with its ultra-powerful infrared vision, would uncover the starter galaxies that they anticipated, and that Hubble couldn’t see.
Ha! said the shiny new telescope. In Webb’s first weeks, as astronomers raced to find the most distant galaxies ever detected, they wondered whether the data were actually wrong. The ancient galaxies were just too big and bright. A recalibration of Webb’s instruments soon showed that some measurements were off, making some galaxies appear more distant than they actually were, and some claims were revised. But the big-picture findings stuck. The early universe was, somehow, bold and brash and remarkably luminous. “The objects we’re finding are as massive or larger than the Milky Way, which is astounding,” said Leja, who co-published a paper last week that identified six enormous galaxies that existed just 500 million to 700 million years after the Big Bang. One of these galaxies may have a mass 100 billion times that of our sun. Our own galaxy similarly contains many billions of stars, but it has had 13 billion years to reach its size.
For a brief moment, this new reality seemed to threaten astronomers’ fundamental understanding of the entire cosmos. If the starting point looked like that, could the standard model of cosmology—our strongest theory about the origins and composition of the universe, the one that didn’t account for what Webb found—be wrong? But astronomers now believe that the theory can accommodate the new telescope’s surprises. Recent computer simulations guided by the standard model have shown that the universe could indeed have created some of the galaxies that Webb has found. “While, on the face of it, the data don’t seem consistent with cosmological models, I think what we’re going to find is it’s not cosmology that’s the problem, but really what we understand about how galaxies formed,” Leja said.
The possible explanations for how astronomers got it wrong are plentiful. Perhaps early stars formed far more efficiently than we thought, through mechanisms that scientists hadn’t considered before. Allison Kirkpatrick, an astronomer at the University of Kansas who studies galaxy evolution, wonders whether cosmic dust in these galaxies could be playing tricks on Webb, making stars appear older than they really are—and maybe cosmic dust was just different back then. Ivo Labbé, an astronomer at Swinburne University of Technology, suspects that black holes could play a role: They are among the most luminous objects in the universe when they’re feeding on cosmic matter, which glows as it gets sucked in. “If you dump a lot of gas into a black hole, it will start to outshine the entire galaxy,” Labbé told me. Such black holes could make early galaxies appear brighter, more star-filled. But none of these possibilities will undo the fact that the first island universes are not what we expected. Even accounting for some weird new phenomena, “everything’s too big, and it’s too big, too soon,” Kirkpatrick told me.
Investigating these questions will require more Webb observations, particularly the kind that yield more detailed measurements of starlight, known as spectroscopy. Astronomers need more to confirm that the most unusual galaxies they’ve found are the real deal. And if they really are as old and big as they seem, understanding their composition will help astronomers suss out the conditions in which they formed. Researchers are in the thick of it now, with fresh spectroscopic data expected to come this spring. The effort verges on soul-searching. Primordial starlight has never been so in demand, and astronomers and theorists—those who observe cosmic wonders, and those who explain them, respectively—don’t know exactly what they’ll find once they’re finished. “It’s probably going to be something like five years until we’ve totally settled into our new universe that we’ve gotten from JWST,” Wren Suess, an astronomer at UC Santa Cruz and Stanford, told me.
In one sense, these new discoveries have injected drama, even anxiety, into a field that was quite stable. “It’s incredible how the universe is just so much weirder than we thought it was,” Erica Nelson, an astronomer at the University of Colorado at Boulder, told me. But in another sense, it’s just fun. When I asked Kirkpatrick whether she feels stressed about the uncertainty her profession is navigating, she cackled with glee. “It’s the beginning of the universe!” she said. “It’s not going to affect my life, so it’s really fun to think about this kind of stuff.”
As I’ve talked with astronomers about what Webb has found so far, one word keeps coming up: shouldn’t. Galaxies shouldn’t be this way; the cosmic dawn shouldn’t be that way. I find these shouldn’ts delightful. They hint at the well-intentioned hubris of humans, especially the most curious ones, those who wish to determine exactly how something works and why. But of course the universe says, speaking to us by way of a giant telescope floating a million miles from Earth, This is how it is. This is, apparently, how it has always been. We’re just discovering the wonder of it now.