Tangles of huge organic molecules are drifting across a distant galaxy, astronomers using the James Webb Space Telescope (JWST) have found. Scientists have never spotted such molecules so far from Earth, and their presence suggests that their host galaxy was busy making stars early in the Universe’s history.
The galaxy is 3.8 billion parsecs (12.3 billion light-years) away so distant that it looks like it was less than 1.5 billion years after the big bang. He must have basically trained with overdrive, says Justin Spilker, an astronomer at Texas A&M University in College Station.
Spilker and his colleagues describe the find today in Nature1. It shows the power of the new JWST, even if the spectrometer aboard the telescope that made the measurement suffered a sudden and startling degradation in performance.
Photographic bombardment galaxy
Seen from Earth, the galaxy, known as SPT0418-47, lies behind another, closer galaxy. The gravity of the intervening galaxy bends and distorts the light of SPT0418-47, making it about 30 times brighter than it would otherwise appear, an effect called gravitational lensing.
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Spilkers’ team wanted to find polycyclic aromatic hydrocarbons (PAHs), which are chemical compounds found in soot and smoke. They also form near massive young stars that emit a lot of ultraviolet light.
By feeding on that energy, the molecules grow large and eventually look like smoke or soot particles floating in space. They help regulate how gas inside galaxies is heated and cooled, and thus help control how new stars are born, says Stacey Alberts, an astronomer at the University of Arizona in Tucson.
Previous studies of SPT0418-47 identified areas where stars could form, but were unable to detect PAHs2. Molecules are hard to spot except in the infrared wavelengths of light, which JWST excels at studying. So Spilker’s team pointed the telescope at the galaxy last August, in what were some of his first scientific observations. Months later, they finally crunched the data and the PAHs emerged.
The molecules appear as bright blobs within the ring of the galaxy. That irregularity surprised Spilker. Wherever we see molecules there are stars forming, but there are also parts in that ring where stars are forming where we don’t see molecules, he says. This is the part that we don’t really understand yet.
Regardless, the PAHs suggest that the galaxy was busy making stars early in the history of the Universe. At a time when the Universe was only 10 percent of its current age, SPT0418-47 already had a mass similar to that of today’s Milky Way.
Other JWST observations have spotted PAHs in nearby galaxies3. But seeing PAHs in this distant galaxy is an important clue to how these molecules form, says Karin Sandstrom, an astronomer at the University of California San Diego. They’re still quite mysterious, and we don’t fully understand how they even form in the Milky Way, she says. Alberts adds that the new discovery will force astronomers to rethink how the dust formed and how it shaped the first generations of stars and galaxies.
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More breakthroughs may or may not be on the way. Spilker and his colleagues are planning to use JWST to search for PAHs in two other gravitationally lensed galaxies. But the telescope’s mid-infrared spectrometer, which is what the team used to study SPT0418-47, is currently experiencing problems.
On May 25, the team running JWST reported that the spectrometer was not collecting as much information as it should in one of the modes it operates in. Two of the four channels it watches in that mode are degrading, in the worst case losing up to 50% of data.
The root cause of this problem is still being investigated, the engineers wrote. The spectrometer continues to function, but the team has worked to carefully quantify the effect of this leak on the scientific data.
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