APS
The new JWST observatory is revealing far more bright galaxies in the early Universe than anyone predicted, and astrophysicists have more than one explanation for the puzzle.
Two weeks after NASA revealed the first images taken by the JWST observatory, scientists woke to the news that cosmology might be broken. Analyzing the JWST’s images, a team of astronomers had spotted a galaxy that shouldn’t be there, at least according to the most frequently used model of the Universe’s evolution, called ΛCDM [1]. The galaxy was inexplicably bright and incredibly young with respect to the current age of the Universe. The initial calculations dated it to just 250 million years after the big bang, when there should not have been enough time for such a galaxy to have evolved. “There was a lot of press given to the idea that the JWST discoveries were a challenge for the basic paradigm of cosmology,” says Rachel Somerville, who studies galaxy formation at the Flatiron Institute, New York.
A flurry of reports of other early-Universe galaxies with anomalously high brightnesses then emerged, leaving astronomers on tenterhooks as to what they might see next [2]. “As more data came in, it became clear that the abundance of early bright galaxies was higher than theorists had predicted,” says Steven Finkelstein, an astrophysicist at the University of Texas at Austin. “It was an incredibly exciting time.”
A year and a half on, and with more data in hand, astronomers have revised the estimated age of the record-breaking galaxy [3]. They say it most likely dates to 1.2 billion years after the big bang, when galaxies were widespread. Theorists have also now largely laid to rest doubts about the ΛCDM model, with the latest nail in the coffin coming from a new study by Nashwan Sabti of Johns Hopkins University, Maryland, and his colleagues that compares predictions of a modified ΛCDM model with Hubble Space Telescope data [4]. “Hubble data are very, very strict when it comes to adding in more galaxies,” Sabti says. “If cosmology were broken, then we should see some sign of that in the Hubble data. We don’t.”
Still, the JWST observations continue to unearth—and confirm—unexpectedly bright early-Universe galaxies, so most astrophysicists agree that a puzzle remains. However, the problem isn’t with the ΛCDM model but with astrophysical models for galaxy and star evolution. Three possible solutions to this puzzle lead the pack, all of which include stars and galaxies in the early Universe behaving very differently from those in the Universe today. “In retrospect, it’s perhaps not surprising that these things were different in the early Universe,” Somerville says. But the assumption that things were the same had been hard coded into models. “With JWST data, that is now changing,” she says.
Red Light Means Go
The JWST observatory was designed to peer farther into the Universe than any other galaxy-imaging telescope. This feat requires two key elements: First, the observatory is equipped with a gargantuan mirror that makes it 100 times more sensitive to faint, distant objects than the Hubble Space Telescope. Second, the observatory detects significantly redder light than its forerunners.
