Did James Webb telescope images 'break' the universe?

In its first images, JWST captured what appeared to be huge galaxies in the ancient universe. In fact, those galaxies looked much too big to fit scientists' current theory of how the universe grew up. This has raised some concerns that the history of the early universe needs to be rewritten.

But a new look at old data from the Hubble Space Telescope tells another story. Perhaps JWST hasn't upended cosmology as much as some scientists feared. Instead, the huge-looking galaxies JWST saw may have simpler explanations.

Researchers shared these findings in the February 9 Physical Review Letters.

JWST is giving us a new language to understand the early universe, says Julian Muñoz. He's a cosmologist at the University of Texas at Austin. "Before we say, 'Hey, we need to throw away everything we knew in cosmology,' we should understand this language."

'Universe breakers'

The trouble began almost as soon as JWST first peered into the distant universe.

When this telescope looks at distant objects, it sees those objects as they appeared far back in time. Why? Because the light from such far-off objects has taken so long to travel to Earth. So when JWST peers at the most distant cosmos, it sees things as they were shortly after the Big Bang.

JWST's first views of such distant, ancient regions of space were confusing in two ways.

First, some of its images contained huge numbers of galaxies. Far more, in fact, than astronomers thought possible so far back in time.

Second, a handful of those galaxies appeared to be monstrously massive. These all dated back to the first 700 million years of the universe. And they were up to 100 times as heavy as scientists thought possible back then. For that reason, these galaxies were dubbed "universe breakers."

Our current understanding of how the universe grew up goes like this. First, dark matter collapsed into giant clumps known as halos. This happened within the first few hundred million years after the Big Bang. The halos' gravity then pulled in normal matter. This eventually formed stars and galaxies.

This would have taken time. Matter would have clumped together slowly, eventually building up larger and larger galaxies. If true, the jumbo galaxies that JWST spied so soon after the Big Bang shouldn't be possible.

What's more, the current story of the universe doesn't predict nearly enough dark matter halos in the early universe as would be needed to build the many big galaxies that JWST saw.

In that light, things look pretty dire for scientists' current theory of how the universe evolved.

But Muñoz and his colleagues think it's too soon to tear up our current picture of how our universe evolved. Perhaps, they say, scientists simply need to be more careful as they interpret data from JWST.

Hubble weighs in

Muñoz's group decided to check JWST's results using data from NASA's Hubble Space Telescope. Hubble is older. And its "eyesight" isn't as good. So it can't see quite as far back in time as JWST can. But both instruments can capture light from galaxies in one era. That era spans roughly 450 million to 750 million years after the Big Bang. JWST views those galaxies in infrared light. Hubble sees their ultraviolet light.

If there really were 10 times more dark matter structures in the early universe than we thought, "there would be 10 times more galaxies in James Webb" images, Muñoz says. And, he adds, "there would also be 10 times more galaxies in Hubble [data]."

But that's not what the Hubble data show.

The team tallied how many galaxies Hubble saw across a wide brightness range. Then, they tried adding more dark matter halos to their model of the early universe. If they added enough halos to match the JWST data, their model could not match the Hubble data.

So … which telescope should we trust?

JWST is the more powerful of the two. It can simply see more galaxies than Hubble can at a given distance. But Hubble has been staring at the universe for much longer, Muñoz notes. JWST started collecting data only in 2022. Hubble has been looking out at the cosmos since 1990. This means that right now, Hubble's data more reliably reflect what's out there, Muñoz argues.

For that reason, the researchers suggest looking at other explanations for JWST's odd galaxies — ones that don't involve rewriting the history of the universe with new physics.

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What's going on?

Scientists thought the galaxies in JWST's images were super massive. They just looked so super bright. But perhaps there's some other reason for their brightness.

Conditions in the early universe might have been different than later on. This may have allowed gas and dust to turn into stars much more efficiently than had been thought. Maybe such speedy star formation created the weirdly bright objects JWST sees.

Star formation also might have been more episodic. That is, there may have been quiet periods with little star formation, followed by periods full of fast star formation. The stars from each burst of star formation would all be close to the same age. So they'd all die as explosive supernovas around the same time, one after another. In that case, JWST might simply be capturing some galaxies at these moments of intense brightness.

It's also possible that some of the light that JWST sees in these early galaxies comes from their centers. There, supermassive black holes could be gorging on the matter around them. That frenzied feast would throw off a lot of light. And that, overall, could make a galaxy look super bright.

Other researchers are impressed by what Muñoz's team found. "It's very clever to look at the overlap region [between Hubble and JWST]," says Priyamvada Natarajan. She's a theoretical astrophysicist at Yale University.

But Erica Nelson points out that the cosmos isn't entirely safe yet. Nelson is an astrophysicist at the University of Colorado Boulder. She was part of the team that first identified the "universe breakers." If any of these objects really is as massive as it looks, she says, "it is a problem."

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Power Words

astronomer: A scientist who works in the field of research that deals with celestial objects, space and the physical universe.

astrophysicist: A scientist who works in an area of astronomy that deals with understanding the physical nature of stars and other objects in space.

Big Bang: The rapid expansion of dense matter and space-time that, according to current theory, marked the origin of the universe. It is supported by astronomers' current understanding of the composition and structure of the universe.

black hole: A region of space having a gravitational field so intense that no matter or radiation (including light) can escape.

colleague: Someone who works with another; a co-worker or team member.

cosmic: An adjective that refers to the cosmos — the universe and everything within it.

cosmology: The science of the origin and development of the cosmos, or universe. People who work in this field are known as cosmologists.

cosmos: (adj. cosmic) A term that refers to the universe and everything within it.

dark matter: Physical objects or particles that emit no detectable radiation of their own. They are believed to exist because of unexplained gravitational forces that they appear to exert on other, visible astronomical objects.

dire: An adjective that means grave, or hard to survive.

galaxy: A group of stars — and usually invisible, mysterious dark matter — all held together by gravity. Giant galaxies, such as the Milky Way, often have more than 100 billion stars. The dimmest galaxies may have just a few thousand. Some galaxies also have gas and dust from which they make new stars.

gravity: The force that attracts anything with mass, or bulk, toward any other thing with mass. The more mass that something has, the greater its gravity.

infrared: A type of electromagnetic radiation invisible to the human eye. The name incorporates a Latin term and means "below red." Infrared light has wavelengths longer than those visible to humans. Other invisible wavelengths include X-rays, radio waves and microwaves. Infrared light tends to record the heat signature of an object or environment.

matter: Something that occupies space and has mass. Anything on Earth with matter will have a property described as "weight."

physics: The scientific study of the nature and properties of matter and energy. Classical physics is an explanation of the nature and properties of matter and energy that relies on descriptions such as Newton's laws of motion. Quantum physics, a field of study that emerged later, is a more accurate way of explaining the motions and behavior of matter. A scientist who works in such areas is known as a physicist.star: The basic building block from which galaxies are made. Stars develop when gravity compacts clouds of gas. When they become hot enough, stars will emit light and sometimes other forms of electromagnetic radiation. The sun is our closest star.

supernova: (plural: supernovae or supernovas) A star that suddenly increases greatly in brightness because of a catastrophic explosion that ejects most (or sometimes all) of its mass.

telescope: Usually a light-collecting instrument that makes distant objects appear nearer through the use of lenses or a combination of curved mirrors and lenses. Some, however, collect radio emissions (energy from a different portion of the electromagnetic spectrum) through a network of antennas.

theoretical: An adjective for an analysis or assessment of something that based on pre-existing knowledge of how things behave. It is not based on experimental trials. Theoretical research tends to use math — usually performed by computers — to predict how or what will occur for some specified series of conditions. Experimental testing or observations of natural systems will then be needed to confirm what had been predicted.

theory: (in science) A description of some aspect of the natural world based on extensive observations, tests and reason. A theory can also be a way of organizing a broad body of knowledge that applies in a broad range of circumstances to explain what will happen. Unlike the common definition of theory, a theory in science is not just a hunch. Ideas or conclusions that are based on a theory — and not yet on firm data or observations — are referred to as theoretical. Scientists who use mathematics and/or existing data to project what might happen in new situations are known as theorists.

ultraviolet light: A type of electromagnetic radiation with a wavelength from 10 nanometers to 380 nanometers. The wavelengths are shorter than that of visible light but longer than X-rays.

universe: The entire cosmos: All things that exist throughout space and time. It has been expanding since its formation during an event known as the Big Bang, some 13.8 billion years ago (give or take a few hundred million years).

Citations

Journal:​ N. Sabti, J.B. Muñoz and M. Kamionkowski. Insights from HST into ultramassive galaxies and early-universe cosmology. Physical Review Letters. Vol. 132, February 9, 2024, 061002. doi: 10.1103/PhysRevLett.132.061002.

Journal: G. Sun et al. Bursty star formation naturally explains the abundance of bright galaxies at cosmic dawn. The Astrophysical Journal Letters. Vol. 955, October 1, 2023, p. L35. doi: 10.3847/2041-8213/acf85a.

Journal: I. Labbé et al. A population of red candidate massive galaxies ~600 Myr after the Big Bang. Nature. Vol. 616, April 13, 2023, p. 266. doi: 10.1038/s41586-023-05786-2.