You can also have a galaxy that is asymmetric for other reasons.” One of those reasons is a clumpy history of star formation that occurs naturally in some galaxies. “If you see a galaxy that’s very asymmetric, that’s usually an indication of a recent merger,” says Vicente Rodriguez-Gomez, an associate professor at the National Autonomous University of Mexico, who was not involved with the new papers. ![]() There is nonetheless a small chance that the object is an unstable galaxy that formed two clusters of stars at different times. Furthering the case for the merger claim, the A component is estimated to be tens of millions of years younger than its companion. The A clump is bluer, mostly free of dust and bursting with baby stars, whereas B is redder, dustier and comparatively lacking in new stars. The two clumps-unpoetically named “A” and “B”-have different colors, amounts of dust and rates of star formation. Its surprising shape looks like a lopsided peanut, and it has two clumps of stars on opposite ends, indicating that it is most likely two galaxies that formed separately before beginning to blend into one. Nevertheless, once JWST was operational, Coe, an astronomer at the Space Telescope Science Institute in Baltimore, Md., knew he had to take another look and tasked Hsiao with analyzing the new observatory’s data.ĭespite its unappetizing name, MACS0647-JD has given astronomers a taste for the diversity of galaxies that formed within the first 500 million years of the universe. Based on its redshift-a measure of how much its light has been stretched into the red end of the spectrum from the expansion of the universe-MACS0647-JD seemed to be the oldest galaxy then known, though even older galaxies have been observed in the years since. It appeared in Hubble’s image three times because of distortion and magnification from a massive cluster of galaxies sitting between it and Earth-an effect called gravitational lensing. At the time, it looked like little more than a red speck. ![]() The observation is described in two papers-one published in the Astrophysical Journal Letters in early June and another currently under peer review-both led by Tiger Yu-Yang Hsiao, a graduate student at Johns Hopkins University.ĭan Coe, principal investigator of the project, first spotted the merging galaxy, MACS0647-JD, with the Hubble Space Telescope about a decade ago. This merger appears to beat the former record holder by a full 300 million years. ![]() The photographs reveal ancient galaxies close to crashing into each other during the first 500 million years after the birth of the universe. A cosmic collision that may be the oldest galaxy merger ever seen has appeared in images from the James Webb Space Telescope (JWST).
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