Astronomers may have discovered the universe’s first galaxies

Astronomers may have discovered the universe’s first galaxies

Astronomers may have discovered the universe’s first galaxies

Scientists have just announced that that they’ve discovered what may be some of the earliest galaxies to form in the universe, a tantalizing discovery made thanks to NASA’s new flagship James Webb Space Telescope.

“This is the first large sample of candidate galaxies beyond the reach of the Hubble Space Telescope,” astronomer Haojing Yan said yesterday at a press conference at the American Astronomical Society meeting in Seattle. Yan, who is a student at the University of Missouri, led the newly published study. Because the more sensitive JWST can see farther into space than its Hubble predecessor, it essentially looks further back in time. In the new catalog of 87 galaxies astronomers have discovered, some may date back to about 13.6 billion years ago, just 200 million years after the Big Bang. Then the galaxies radiated the light we see today – although those systems of stars, gas and dust would have changed drastically since then, if they existed at all.

While scientists have studied other distant galaxies dating back to when the universe was young, Yan and his colleagues’ discoveries could break those records by a few hundred million years or so. But at this point, all of them are still considered “candidate galaxies,” meaning their birthdates have yet to be confirmed.

Dating a galaxy can be a challenging business: It involves measuring its “redshift,” how much the light it emits is stretched into longer red wavelengths, which tells astronomers how fast the galaxy is moving away from us in the rapidly expanding universe . That, in turn, tells astronomers the distance of the galaxy from Earth — or rather, the distance the photons from its stars had to travel at the speed of light before reaching a space telescope near Earth like JWST. Light from stars in the farthest galaxy in this collection may have been emitted 13.6 billion years ago, likely quite soon after the young galaxy converged.

These newly estimated distances will need to be confirmed with spectra, which involves measuring the light the galaxies emit across the electromagnetic spectrum and determining their unique characteristics. Still, Yan expects many of them to be correctly dated to the early days of the cosmos: “I bet $20 and a large beer that the success rate will exceed 50 percent,” he said.

Yan’s team has imaged these galaxies with JWST’s NIRCam at six near-infrared wavelengths. To estimate their distances, the astronomers used a standard “drop-out” technique: hydrogen gas surrounding galaxies absorbs light at a certain wavelength, so the wavelengths at which an object can or cannot be seen put a limit on how far away it is likely to be. These 87 candidate galaxies mostly look like blobs that can only be detected in the longer (and thus redder) near-infrared wavelengths detectable by NIRCam, which could mean they are very distant and therefore very old.

However, it’s possible that some of them are much closer than expected, which would mean they’re not that old after all. For example, their light may simply be too dim to be detected at some wavelengths. Until Yan can collect more detailed data, he won’t know for sure.



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