AUSTIN, Texas — The James Webb Space Telescope (JWST) appears to be finding multiple galaxies that grew too massive too soon after the Big Bang, if the standard model of cosmology is to be believed.
In a study published in Nature Astronomy, researchers at The University of Texas at Austin find that six of the earliest and most massive galaxy candidates observed by JWST stand to contradict the prevailing thinking in cosmology. That’s because other researchers estimate that each galaxy is seen from between 500 million and 700 million years after the Big Bang, yet measures more than 10 billion times as massive as our sun. One of the galaxies even appears to be more massive than the Milky Way, despite the fact that our own galaxy had billions of more years to form and grow.
“If the masses are right, then we are in uncharted territory,” said Mike Boylan-Kolchin, associate professor of astronomy who led the study. “We’ll require something very new about galaxy formation or a modification to cosmology. One of the most extreme possibilities is that the universe was expanding faster shortly after the Big Bang than we predict, which might require new forces and particles.”
For galaxies to form so fast at such a size, they also would need to be converting nearly 100% of their available gas into stars.
“We typically see a maximum of 10% of gas converted into stars,” Boylan-Kolchin said. “So while 100% conversion of gas into stars is technically right at the edge of what is theoretically possible, it’s really the case that this would require something to be very different from what we expect.”
Despite all of the breathless excitement it evokes, JWST has presented astronomers with an unsettling problem. If the masses and time since the Big Bang are confirmed for these galaxies, fundamental changes to the reigning model of cosmology — what’s called the dark energy plus cold dark matter paradigm — could be needed. If there are other, faster ways to form galaxies than the current model allows, or if more matter actually was available for forming stars and galaxies in the early universe than was previously understood, astronomers would need to shift their prevailing thinking.
The six galaxies’ ages and masses are initial estimates and will need follow-up confirmation with spectroscopy, a method that splits the light into a spectrum and analyzes the brightness of different colors. Such analysis might suggest that central supermassive black holes, which could heat up the surrounding gas, may be making the galaxies brighter so that they look more massive than they really are. Or perhaps the galaxies are actually seen at a time much later than originally estimated due to dust that causes the color of the light from the galaxy to shift redder, giving the illusion of being more light-years away and, thus, further back in time.
The galaxy data comes from the Cosmic Evolution Early Release Science Survey, a multi-institution JWST initiative led by UT Austin astronomer Steven Finkelstein.
The initial discovery and estimates of the six galaxy candidates’ masses and redshifts were published in Nature in February by a team led by Swinburne University of Technology in Australia. The research is supported by the National Science Foundation and NASA.
