The Early Release Observations (EROs) of JWST beautifully demonstrate the promise of JWST in characterizing the universe at Cosmic Dawn. A recent investigation of distant galaxies captured by NASA’s James Webb Space Telescope reveals that they are remarkably similar to “green peas,” a rare class of small galaxies in our cosmic backyard and very young.
Green pea galaxies were discovered and named in 2009 by volunteers participating in Galaxy Zoo. In this project, citizen scientists help classify galaxies in images, starting with those from the Sloan Digital Sky Survey. Small, rounded, unresolved specks with a particular green hue were distinguished as peas in the survey’s composite images and a characteristic of the galaxies themselves.
Because a significant portion of the light in green pea galaxies comes from brilliantly blazing gas clouds, these galaxies have distinctive colors. Unlike stars, which produce a rainbow-like spectrum of continuous color, gases emit light at specific wavelengths. Peas are typically only 5,000 light-years across, or roughly 5% the size of our Milky Way galaxy. They are also relatively small.
Keunho Kim, a postdoctoral researcher at the University of Cincinnati and a member of the analysis team, said, “Peas may be small, but their star-formation activity is unusually intense for their size, so they produce bright ultraviolet light. 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.”
James Rhoads, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said, “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.”
Stars convert lighter elements like hydrogen and helium into heavier ones as they generate energy. These heavier elements are integrated into the gas that creates the following stellar generations after stars burst or shed their outer layers at the end of their lives, continuing the process. Throughout the universe’s history, stars have steadily improved it.
Two of the Webb galaxies had oxygen levels that are about 20% lower than those of the Milky Way. Despite making up fewer than 0.1% of the nearest galaxies seen by the Sloan survey, they resemble ordinary green peas. Even more, the peculiarity is present in the third analyzed galaxy.
Goddard researcher Sangeeta Malhotra said, “We’re seeing these objects as they existed up to 13.1 billion years ago when the universe was about 5% its current age. And we see they are young galaxies in every sense – full of young stars and glowing gas containing few chemical products recycled from earlier stars. Indeed, one of them contains just 2% the oxygen of a galaxy like ours and might be the most chemically primitive galaxy yet identified.”