A new analysis of distant galaxies imaged by NASA’s James Webb Space Telescope shows that they are extremely young and share some remarkable similarities to “green peas,” a rare class of small galaxies in our cosmic backyard.
“With detailed chemical fingerprints of these early galaxies, we see that they include what might be the most primitive galaxy identified so far.
At the same time, we can connect these galaxies from the dawn of the universe to similar ones nearby, which we can study in much greater detail,” said James Rhoads, an astrophysicist at NASA's Goddard Flight Centre in Greenbelt, Maryland, who presented the findings at the 241st meeting of the American Astronomical Society in Seattle.
A paper describing the results, led by Rhoads, was published Jan. 3 in The Astrophysical Journal Letters.
Green pea galaxies were discovered and named in 2009 by volunteers taking part in Galaxy Zoo, a project where citizen scientists help classify galaxies in images, starting with those from the Sloan Digital Sky Survey.
Peas stood out as small, round, unresolved dots with a distinctly green shade, a consequence of both the colors assigned to different filters in the survey’s composite images and a property of the galaxies themselves.
“Peas may be small, but their star-formation activity is unusually intense for their size, so they produce bright ultraviolet light,” said Keunho Kim, a postdoctoral researcher at the University of Cincinnati and a member of the analysis team. “Thanks to ultraviolet images of green peas from Hubble and ground-based research on early star-forming galaxies, it’s clear that they both share this property.”
In July 2022, NASA and its partners in the Webb mission released the deepest and sharpest infrared image of the distant universe yet seen, capturing thousands of galaxies in and behind a cluster known as SMACS 0723. The cluster’s mass makes it a gravitational lens, which both magnifies and distorts the appearance of background galaxies.
Among the faintest galaxies behind the cluster were a trio of compact infrared objects that looked like they could be distant relatives of green peas. The most distant of these three galaxies was magnified by about 10 times, providing a significant assist from nature on top of the telescope’s unprecedented capabilities.
Webb did more than image the cluster – its Near-Infrared Spectrograph (NIRSpec) instrument also captured the spectra of selected galaxies in the scene.
When Rhoads and his colleagues examined these measurements and corrected them for the wavelength stretch resulting from the expansion of space, they saw characteristic features emitted by oxygen, hydrogen, and neon line up in a stunning resemblance to those seen from nearby green peas.