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A new analysis of distant galaxies recorded by the James Webb Space Telescope (JWST) shows that they share properties with a rare class of galaxies called “green peas” found in our cosmic backyard.
One of these galaxieswhich existed when the Universe was only 5% of its current age, may be one of the most “chemically primitive” galaxies astronomers have ever seen.
“With detailed chemical fingerprints of these early galaxies, we see that they contain perhaps the most primitive galaxy yet identified,” said research leader James Rhoads, an astrophysicist at NASA’s Goddard Space Flight Center in Maryland, in a expression. “At the same time, we can connect these galaxies from the beginning of the Universe with similar ones nearby that we can study in much more detail.”
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“Green pea” galaxies were discovered in observations from the Sloan Digital Sky Survey in 2009. Green peas are so named because they stand out as small, round, unresolved dots with a distinct green hue. They appear green because much of the light from these rare galaxies comes from bright, glowing gas clouds that emit light at specific wavelengths, rather than from the broad spectrum of light and continuous colors that they emit Stars in other galaxies.
These green pea galaxies are rare, accounting for only 0.1% of nearby galaxies. They’re also (cosmically) compact, with diameters of just 5,000 light-years — just 5% the width of our galaxy, the Milky Way. But what green pea galaxies lack in size, they seem to make up for in star-forming rate.
“Peas may be small, but their star-forming activity is unusually intense for their size, so they produce bright ultraviolet light,” Keunho Kim, a postdoctoral researcher at the University of Cincinnati and a member of the analysis team, said in the statement. “Thanks to ultraviolet images of Hubble green peas and ground-based research on early star-forming galaxies, it’s clear they both share this property.”
Green peas in the early universe
In July 2022, the JWST team unveiled the deepest and sharpest infrared image of the distant universe ever recorded, which captured the galaxies in and behind a galaxy cluster called SMACS 0723.
As a result of a phenomenon called gravitational lenses, SMACS 0723 enlarges and distorts the appearance of the galaxies beyond. The image showed a trio of infrared objects resembling the distant relatives of local galaxies, the green pea.
SMACS 0723’s gravitational lensing magnified the most distant of these galaxies by a factor of 10, giving the space telescope a massive natural observation boost.
Using its Near-Infrared Spectrograph (NIRSpec) instrument, JWST also obtained the spectra of the galaxies in the image, revealing the telltale signs of oxygen, hydrogen and neon emissions, further enhancing the resemblance to green pea galaxies.
This spectrographic data allowed the team to measure the amount of oxygen in these distant and early galaxies for the first time, and showed that two of these galaxies contain about 20% of the oxygen that the Milky Way contains.
As stars die, they enrich the universe with heavy elements that they forged during their lives, which means that early galaxies like these should have relatively few elements heavier than hydrogen and helium compared to older galaxies like ours. which astronomers refer to as “metals”.
“We see these objects as they existed 13.1 billion years ago, when the universe was about 5% of its current age,” Sangeeta Malhotra, a NASA Goddard researcher and research team member, said in the statement. “And we see that they are young galaxies in every respect – full of young stars and glowing gas that contains few chemical products recycled from previous stars.”
However, the third of these early lens galaxies is more unusual. “One of them contains only 2% of the oxygen of a galaxy like our own and could be the most chemically primitive galaxy identified so far,” Malhotra said.
The team’s research was published on January 3rd The Letters of the Astrophysical Journal and was presented at the 241st meeting of the American Astronomical Society in Seattle on January 9th.
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