The James Webb Space Telescope (JWST) appears to find several galaxies that became too massive too soon after the Big Bang, if the Standard Model of cosmology is to be believed.

In a study published in natural astronomyMike Boylan-Kolchin, associate professor of astronomy at the University of Texas at Austin, finds that six of the oldest and most massive candidate galaxies observed by the JWST so far contradict mainstream thinking in cosmology.

Indeed, other researchers estimate that each galaxy is seen between 500 and 700 million years after the Big Bang, yet is over 10 billion times more massive than our sun. One of the galaxies even appears to be more massive than the Milky Way, although our own galaxy had billions of extra years to form and grow.

“If the masses are right, then we’re in uncharted territory,” Boylan-Kolchin said. “We will need something very new about galaxy formation or a change in cosmology. One of the more extreme possibilities is that the universe expanded more rapidly soon after the Big Bang than we don’t expect, which may require new forces and particles.”

For galaxies to form so quickly at such a size, they would also have to convert nearly 100% of their available gas into stars.

“We typically see a maximum of 10% gas converted into stars,” Boylan-Kolchin said. “So while converting 100% of the gas into stars is technically at the limit of what is theoretically possible, it is true that it would require something quite different from what we expect.”

For all the breathless excitement it evokes, JWST has presented astronomers with a troubling dilemma. If the masses and time since the Big Bang are confirmed for these galaxies, fundamental changes to the reigning pattern of cosmology – the so-called Dark Energy + Cold Dark Matter (ΛCDM) paradigm, which has guided cosmology since late 1990s – might be needed.

Whether there are other faster ways to form galaxies than ΛCDM allows, or whether there was more material available to form stars and galaxies in the early universe than previously thought , astronomers should change their mainstream way of thinking.

The times and masses of the six galaxies are initial estimates and will require further confirmation by spectroscopy, a method that splits light into a spectrum and analyzes the brightness of different colors. Such an analysis could suggest that central supermassive black holes, which could heat up surrounding gas, could make galaxies brighter, so they appear more massive than they really are.

Or maybe the galaxies are actually seen at a time much later than originally expected due to dust causing the color of the galaxy’s light to turn redder, giving the illusion of being more light-years and therefore further in time.

Data on the galaxy come from the Cosmic Evolution Early Release Science Survey (CEERS), a multi-agency JWST initiative led by UT Austin astronomer Steven Finkelstein.

Another ongoing JWST collaborative project, COSMOS-Web, co-led by Caitlin Casey of UT Austin, may be involved in spectroscopy and shed more light on the results to help resolve the dilemma. COSMOS-Web covers an area about 50 times larger than CEERS and is expected to discover thousands of galaxies.

“It will be ideal for discovering the rarest and most massive galaxies in early times, which will tell us how the largest galaxies and black holes in the early universe arose so quickly,” Boylan-Kolchin said.

The initial discovery and estimates of the masses and redshifts of the six candidate galaxies were published in Nature in February by a team led by Swinburne University of Technology in Australia.