Cosmic controversy: James Webb Telescope findings challenge best-established theories

The galaxies are much more massive than theoretical predictions would indicate for the age they are estimated to be, which is between 500 and 700 million years old. 

The researchers estimate that in order for the galaxies to reach their size in this time period, they would need to be converting nearly 100% of their available gas into stars. In contrast, astronomers typically see no more than 10% of gas converted into stars.

In a news release, Boylan-Kolchin pointed out that "If the masses are right, then we are in uncharted territory.”

Accounting for the differences between the predictions and reality would likely require changes in cosmological theory, possibly reinventing how we understand galaxy formation. The leading model of cosmology dates from the late 1990s and is termed the ΛCDM (Lambda CDM, or LCDM), also known as the dark energy + cold dark matter (ΛCDM) paradigm.

What might be possible, for example, is that new forces and particles exist which would explain how the universe expanded faster than we currently think right after the Big Bang. Another possibility is that more matter was available for forming stars and galaxies in the early universe than is currently understood.

The data on the galaxies used in the study was obtained from the Cosmic Evolution Early Release Science Survey (CEERS).

Interesting Engineering (IE) reached out to Professor Boylan-Kolchin for more insight into his paper.

The following exchange has been lightly edited for clarity and flow.

Interesting Engineering: What are the implications of the possibility that the universe was expanding faster after the Big Bang than prevailing theories suggest?

Professor Boylan-Kolchin: If the Universe expanded faster early in its history (the models typically have this happening for a short period near redshift of 3500 or near ~50,000 years after the big bang), then one implication is that the Universe would be somewhat younger than we currently believe. We now have a precise measurement of 13.8 Gyr (with an error of < 0.2%!) for the age of the Universe in the standard 6-parameter dark energy + cold dark matter (LCDM) model, but faster expansion would be an extension to this model and would require an age of closer to 12.8 or 13.0 billion years. This is one tangible example. [The] structure would also grow faster, somewhat paradoxically, because we’d require extra matter to ‘balance out’ that early expansion and this would help promote earlier growth of galaxies (perhaps matching JWST observations better).

These models for faster early expansion — some go by the name “Early Dark Energy” — were actually originally proposed to solve the Hubble tension, which is the discrepancy between measurements of the expansion rate based on cosmological data from early times (which is very precise but is indirect) vs. late times (which is direct but can be somewhat trickier). The extra early expansion would change our inference of the present expansion rate derived from early cosmological data to match the locally-measured rate (the universe would be expanding a little faster today than we’d have otherwise thought based on the early cosmological data). So, in that sense, this proposed early faster expansion *could* explain 2 separate ’tensions.’

IE: If the galaxies formed that fast, were they converting up to 100% of available gas into stars while typically only up to a 10% conversion is seen?

A 100% efficiency is not physically realistic, as it would imply that even all very diffuse gas far away from the galaxy (which forms at the center of a much larger halo of dark matter) would have to be converted into stars — and that’s just not possible in any model that we can think of. But, there are some proposals for a conversion efficiency that could be substantially higher than 10%, however, there are good reasons to take these seriously.

One reason that star formation is relatively inefficient in general is “feedback”: basically, stars themselves put energy back into surrounding gas, which heats that gas up and slows down subsequent star formation. Accretion onto supermassive black holes is another example of feedback that can inhibit star formation (and explain why it is only ~10% efficient typically). It could be that in the early Universe, feedback hasn’t had a chance to be as effective. Some people are proposing different modes of galaxy formation at early times will be conducive to feedback-free star formation as well. 

(Of course, another possibility is that the galaxies aren’t quite as massive as people are currently measuring, which can happen in a number of ways.)

IE: Does the JWST data suggest that our understanding of the Big Bang may be incorrect? 

No, this does not call the Big Bang into question at all. The Big Bang is an idea that the Universe originated in a singularity, was much hotter and denser at very early times, and then expanded and cooled, leading to the nucleosynthesis of hydrogen into helium and later leaving relic radiation (the cosmic microwave background, CMB) that we can detect today. All of this is extremely well tested, and any model will have to match those observational facts (which is basically what we mean by the Big Bang). 

The LCDM model is one implementation of a cosmology does this, and does so highly successfully, but there is room for additions to the model (early dark energy would be such an addition/extension to the LCDM model). Completely throwing out the LCDM model is possible, but any replacement would have to reproduce its successes while explaining observations that the LCDM model doesn’t. No such model exists at present.

IE: Can we confirm how fast the universe was expanding in the beginning? 

Precision measurements of the CMB [cosmic microwave background], which are underway and should be made public soon, should be able to test whether the Universe had a brief period of faster-than-expected expansion at very early times. These data will come from the Atacama Cosmology Telescope (and possibly from the South Pole Telescope), and the data should be able to tell us whether there is evidence for such an expansion or if any deviations from the standard expansion history that are enough to explain the Hubble tension (and possibly these early galaxies) are ruled out by the data.

Check out his new paper, “Stress testing ΛCDM with high-redshift galaxy candidates,” in Nature Astronomy.

Study abstract

Early data from the James Webb Space Telescope (JWST) have revealed a bevy of high-redshift galaxy candidates with unexpectedly high stellar masses. An immediate concern is the consistency of these candidates with galaxy formation in the standard ΛCDM cosmological model, wherein the stellar mass (M⋆) of a galaxy is limited by the available baryonic reservoir of its host dark matter halo. The mass function of dark matter haloes therefore imposes an absolute upper limit on the number density n (>M⋆, z) and stellar mass density ρ⋆ (>M⋆, z) of galaxies more massive than M⋆ at any epoch z. Here I show that the most massive galaxy candidates in JWST observations at z ≈ 7–10 lie at the very edge of these limits, indicating an important unresolved issue with the properties of galaxies derived from the observations, how galaxies form at early times in ΛCDM or within this standard cosmology itself.