Astronomers discover tiny galaxy with extraordinary star formation in distant Universe

Image of the tiny galaxy RX J2129-z95 discovered thanks to JWST. Formed just 500 million years after the Big Bang. Their study could help astronomers learn more about galaxies that existed shortly after the Big Bang.  Credit: ESA/Webb, NASA y CSA, P. Kelly

Using first-of-their-kind observations from the James Webb Space Telescope (JWST), an international scientific team, in which the Instituto de Astrofísica de Canarias (IAC) participates, finds a unique, minuscule galaxy that emitted its light more than 13 billion years ago. The galaxy, detected through gravitational lensing, is one of the smallest ever discovered at this distance and has an extremely high star formation rate for its size. This discovery could help astronomers learn more about galaxies that were present shortly after the Universe came into existence. The paper is published in Science.

“This galaxy is far beyond the reach of all telescopes except the James Webb, and these first-of-their-kind observations of the distant galaxy are spectacular,” says Patrick Kelly, a researcher at the University of Minnesota who co-led the study. “Here, we’re able to see most of the way back to the Big Bang, and we've never looked at galaxies when the universe was this young in this level of detail. The galaxy’s volume is roughly a millionth of the Milky Way’s, but we can see that it’s still forming the same numbers of stars each year.”

The JWST can observe a wide enough field to image an entire galaxy cluster at once. The researchers were able to find and study this new, tiny galaxy because of a phenomenon called gravitational lensing—where mass, such as that in a galaxy or galaxy cluster, bends and magnifies light. A galaxy cluster lens caused this small background galaxy to appear 20 times brighter than it would if the cluster were not magnifying its light.

The researchers then used spectroscopy to measure how far away the galaxy was, in addition to some of its physical and chemical properties. “The galaxies that existed when the Universe was in its infancy are very different from what we see in the nearby Universe now,” explains Hayley Williams, first author on the paper and a Ph.D. student at the Minnesota Institute for Astrophysics. “This discovery can help us learn more about the characteristics of those first galaxies, how they differ from nearby galaxies, and how the earlier galaxies formed.”

The JWST can collect about six times as much light as the Hubble Space Telescope and is much more sensitive at redder, longer wavelengths in the infrared spectrum. This allows scientists to access an entirely new window of data. “The James Webb Space Telescope has this amazing capability to see extremely far into the universe. We're seeing things that previous telescopes would have ever been able to capture. It’s basically getting a snapshot of our universe in the first 500 million years of its life, " says Ismael Pérez-Fournon, a researcher at the IAC and the University of La Laguna (ULL) who has participated in the study. "Moreover, the increase in brightness provided by the gravitational lensing effect of the galaxy cluster is equivalent to observing this tiny galaxy with a telescope such as the Webb telescope with a diameter of more than 100 m," he adds.

Studying galaxies that were present when the Universe was this much younger can help scientists get closer to answering a huge question in astronomy regarding how the Universe became reionized, that is, the process that caused the Universe to return to being composed of ionised plasma and the cosmos to begin to look as we know it," concludes Frédérick Poidevin, a researcher at the IAC and co-author of the paper.

Article: Hayley Williams, Patrick Kelly et al. “A magnified compact galaxy at redshift 9.51 with strong nebular emission lines”. Science, Apr 2023 DOI: 10.1126/science.adf5307

Contact at the IAC:
Ismael Pérez-Fournon, ipf [at] (ipf[at]iac[dot]es)
Frédérick Poidevin, frederick.poidevin [at] (frederick[dot]poidevin[at]iac[dot]es)

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