The view of the ancient universe revealed by the James Webb Space Telescope (JWST), the most powerful observatory ever launched, is so unexpected that scientists think it might pose a fundamental challenge to our basic understanding of the cosmos, reports a new study.
The telescope has glimpsed inexplicably massive galaxies that formed some 500 to 700 million years after the Big Bang, leaving researchers baffled about how such galactic behemoths managed to emerge so early in cosmic history. The existence of these galaxies may present a serious challenge to the standard model of cosmology, also known as the Lambda cold dark matter (ΛCDM) model, which is an extremely well-corroborated framework that accurately predicts many phenomena in the universe.
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JWST endured a string of delays before it finally made its way to space, but its results have proved to be well worth the wait. Launched on Christmas Day 2021, the telescope has revolutionized our perspective on the cosmos with its unprecedented sensitivity. From its perch about a million miles from Earth, JWST has captured extraordinary shots of our solar backyard, while also peering deep more than 13 billion years into the past, at an era when some of the first stars and galaxies were taking shape.
In addition to its stunning pictures, JWST has also pinpointed puzzling views that were impossible with previous telescopes. For instance, the telescope has spotted several galaxies in the early universe that appear to be utterly gargantuan, with masses ranging from 10 billion to 100 billion times that of our Sun. Put simply: These galaxies shouldn’t exist, according to rules laid out in the standard model.
Michael Boylan-Kolchin, a cosmologist at the University of Texas at Austin, has now revealed how these galaxies are “stress testing” ΛCDM, exposing “an important unresolved issue with the properties of galaxies derived from the observations,” according to a study published on Thursday in Nature Astronomy.
“The results have been a real surprise for me, and it’s been a very exciting period,” Boylan-Kolchin said in an email to Motherboard. “I have never seen anything like the frenzy of activity and results that accompanied the release of the first data!”
“I’m a theorist, so I don’t analyze the images myself, but I remember downloading the first images on my phone as soon as they were made public and feeling a sense of amazement at the accomplishment, that humans can peer back virtually to the edge of what is possible to see and to capture the earliest phases of galaxy formation,” he continued.
Indeed, JWST’s images are jaw-dropping on a pure aesthetic level, but Boylan-Kolchin and other scientists have also found many riddles in the telescope’s observations, including those massive galaxies that appear some 500 million years after the Big Bang.
“These objects really do appear to be early behemoths,” Boylan-Kolchin noted. “They are so massive that we do not expect to have enough collections of atomic matter in the Universe at that time to give rise to that much stellar content.”
So how did these galaxies get so big so fast? JWST’s observations suggest that the answer may be linked to the rapid growth of supermassive black holes during the same time period. Virtually all modern galaxies contain a supermassive black hole at their centers, including the Milky Way, suggesting that this is a core feature of large galactic structures. If black holes in the early universe were able to grow to huge masses in a short timeframe, it might explain why so many massive galaxies are showing up in the telescope’s images—though this explanation essentially trades out one mystery for another.
“The early data from JWST suggest that massive black holes are perhaps even more prevalent at early times than astrophysicists had thought; right now, this seems like perhaps the most likely scenario for explaining these galaxies,” Boylan-Kolchin said. “However, that’s just a hypothesis right now, and it will take a lot more work to confirm or refute this possibility.”
“And if it does turn out that massive black holes are making these galaxies appear more massive than they truly are, then we will have other puzzles to understand: how did so many black holes grow so massive so quickly in the early Universe?” he added.
It’s also conceivable that some unknown mechanism in the early universe supercharged the process of star formation, which could explain why these early galaxies appear so massive and bright. Another mind-boggling possibility is that these galaxies are packed with a group of stars called Population III, which are the first stars that ever shone in the universe. Spotting these stellar ancestors has been a major goal in astronomy for decades, but it’s extremely difficult to see objects that are this far away in time and space. Population III stars are expected to be brighter and more massive than their descendants, which hints that they might be hidden away in the strange galaxies seen by JWST.
If none of these explanations ultimately fit, however, it may be time to consider whether these ancient galaxies have exposed a fundamental gap in our understanding of the universe.
“Perhaps the observations are telling us that our standard and very successful ΛCDM cosmology is incomplete, that we’re missing a component,” Boylan-Kolchin said. “There are clues that this is the case: calculations of the expansion rate of the Universe based on measurements at early cosmic epochs don’t agree with direct measurements in the local Universe, for example. And some proposed solutions to this disagreement, which is called the ‘Hubble tension,’ involve adding additional dark energy at very early times, only 50,000 years after the Big Bang.”
“An interesting byproduct of these ‘early dark energy’ models is that they predict faster evolution of structure and more structure at high redshift, which is exactly what would help explain the existence of these massive early galaxies,” he added. “It is intriguing that a single solution might explain both of these observational discrepancies.”
One thing is clear: Scientists have their work cut out for them in terms of unraveling the true meaning of these bizarre images. To that end, future observations can help to confirm that these galaxies really are that massive, and astronomers also plan to look at much bigger patches of sky to make sure they aren’t seeing a fluke that is limited to one region. For now, though, we will all have to uneasily sit with the unexplained presence of these galactic giants at the edge of space and time.
“Both paths are being actively pursued by scientists,” Boylan-Kolchin concluded. “In fact, that makes this field even more exciting: these are questions we should be able to answer in a matter of months or a couple of years, not decades. I can’t wait to see what we find and what other surprises await us!”
