The galaxy on the screen represented an early population, but the most ancient galaxy discovered by JWST so far existed only 280 million years after the Big Bang. The telescope’s bewildering discovery of bright, early galaxies initially led some scientists to suggest that our understanding of fundamental cosmology, the laws that govern the behavior of energy and matter in the early universe, may be flawed. But after a few years of studying these primitive objects, theorists now have several models to explain their brightness and abundance.
“We almost have gone from having too many early galaxies to having too many theories to explain them,” Somerville told the room.
Perhaps the first galaxies converted gas to stars more efficiently than previously thought. Or they experienced periodic bursts of star formation driven by turbulent conditions. Or maybe early star-forming regions preferentially created massive, extremely bright stars. Many astrophysicists think some combination of these factors, and perhaps others, contributed to the galaxies’ development.
To test these new ideas, researchers are exploring the infant universe through simulations. “There’s actually been really remarkable progress since Webb launched, really in the last year or so, on numerical simulations,” Somerville told attendees, adding that these new simulations “perhaps are more appropriate and more informative for interpreting observations in the high-redshift universe.”
As these models improve, JWST is documenting more and more galaxies. By comparing what it sees in the early universe to simulations that attempt to explain why, researchers are inching closer to uncovering the true nature of cosmic dawn.
“We can try to match the best analogue of the observed galaxy to the simulated,” said Hakim Atek, an astrophysicist with the Paris Institute of Astrophysics at Sorbonne University. “Once you have this best match, you can look at the star formation history, because in the simulations you have access to the whole history of the galaxy.”
An intriguing clue has recently emerged from JWST’s Mid-Infrared Instrument (MIRI), a supercooled device that can split apart the light of distant objects. MIRI has revealed that early galaxies do not have the same traits, as scientists assumed.
“The main surprise is the diversity of the properties of galaxies we are seeing at early epochs,” Atek said. “You’re expecting that they would look the same.”
This diversity may be an indication of star formation that occurred in bursts, as galaxies cycled through periods of fusing stars that exploded and expelled gas clouds, halting the creation of stars, only for the gas to gather again and trigger a new wave of stellar birth.
“Some of them, it looks like they cleared all the interstellar medium that is present there, the gas and the dust. It’s like you’re looking only at naked stars,” Atek said. “Another galaxy is the opposite. It has a lot of gas.”
A further clue comes from a group of galaxies with an overabundance of nitrogen. The presence of the element suggests that there may have been a lot of particularly massive stars in the early universe. In simulations, these massive stars generate an excess of nitrogen before exploding in supernovas and scattering the element across their host galaxies.
Someday, researchers may uncover the full picture of galactic formation. Until then, they’ll continue sifting through the traces in new observations and simulations.
The Puzzle of Existence
Once the astral lights switched on, the universe transformed. Radiation from early galaxies and black holes ionized a sea of neutral hydrogen gas, carving out immense bubbles amid the cosmic haze. Researchers call this period reionization, as it was the second time the universe was ionized. It marks the end of the cosmic dark age, when the foggy abyss was devoid of stars.
The first stars, thought to be hundreds or thousands of times more massive than the sun, furiously worked their way through their hydrogen and helium fuel and erupted in powerful supernovas, seeding the universe with new elements such as carbon, nitrogen, oxygen, phosphorus, and iron — the stuff of planets and of life.
In many ways, those first stars are the mothers of the universe. “We’re looking back at what created us,” said Lise Christensen, an astrophysicist with the Cosmic Dawn Center.
Fitting, perhaps, that the recent conference to discuss cosmic origins took place in Helsingør, down the road from the castle that inspired Elsinore in Hamlet. In the play, Shakespeare’s Danish prince laments:
this brave o’erhanging
firmament, this majestical roof, fretted
with golden fire — why, it appeareth nothing to me
but a foul and pestilent congregation of vapors.
What a piece of work is a man, how noble in
reason, how infinite in faculties
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
yet, to me, what is this quintessence of dust?
Though it’s a mournful rumination on existence — the universe as “a foul and pestilent congregation of vapors,” humanity as the “quintessence of dust” — we now understand that Hamlet’s description is more scientifically accurate than Shakespeare could have known. We are in fact made of elements forged in stars and ejected into the void as gas and dust.
Unlike Hamlet wallowing in Elsinore, however, scientists who study the origins of the universe are exhilarated by these cosmic beginnings.
Editor’s note: The Flatiron Institute is funded by the Simons Foundation, which also funds this editorially independent magazine. Simons Foundation funding decisions have no influence on our coverage.