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 category of tiny and young galaxies.
NASA, ESA, CSA, and STScI
The Discovery of Green Peas
Volunteers working on Galaxy Zoo, a project where citizen scientists help categorize galaxies in photographs starting with those from the Sloan Digital Sky Survey, made the discovery and naming of green pea galaxies in 2009.
According to NASA, peas are tiny, rounded, unresolved specks with a striking green hue caused by colors assigned to various filters in the composite photos and a characteristic of the galaxies themselves.
Due to a significant portion of its light emanating from incandescent gas clouds, green pea galaxy colors are rare. Gases from peas release light at particular wavelengths, as opposed to stars, which produce a spectrum of continuous color resembling a rainbow.
They are only 5,000 light-years across, or roughly 5% the size of our Milky Way galaxy. Webb's deep-field image may have captured some of these rare galaxies.
"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," James Rhoads, an astrophysicist at NASA's Goddard Space Flight Center, said in a statement.
The deepest and brightest infrared image of the distant universe ever seen was released in July 2022 by NASA and its Webb mission collaborators. It showed thousands of galaxies from the SMACS 0723 galaxy cluster.
Due to its mass, the cluster acts as a gravitational lens, enlarging and warping the image of background galaxies. A triad of small infrared objects that appeared distant relatives of green peas was among the weakest galaxies captured behind the cluster.
The furthest of these three galaxies was magnified roughly ten times thanks to Webb's powerful vision.
The typical features released by oxygen, hydrogen, and neon lined up in a striking resemblance to those seen from neighboring green peas when Rhoads and his colleagues studied these measurements and corrected them for the wavelength stretch caused by the expansion of space.
According to NASA, the Webb spectra also allowed for the first measurement of the oxygen content in these cosmic dawn galaxies.
About 20% less oxygen than our Milky Way is present in two Webb galaxies. They appear like common green peas, although they only make up less than 0.1% of the nearest galaxies that the Sloan survey has seen.
According to Goddard researcher Sangeeta Malhotra, these objects appear to have lived up to 13.1 billion years ago, when the universe was only 5% as old as it is now.
Malhotra adds that one may be the most chemically primitive galaxy yet discovered because it has only 2% of the oxygen of a galaxy like ours.
The findings of the team were published in The Astrophysical Journal Letters.
