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The Webb Space Telescope Is a Time Machine


A recently discovered galaxy resembles a tomato that has been squished or perhaps the top of a cherry-flavored Ring Pop. Just a red blob, so hazy and without edges that I had to double-check that my contacts were in before I even looked. I say these things because I'm not sure how we could even begin to comprehend what this cosmic object is—not just a galaxy, but possibly the most distant galaxy we have ever seen—without invoking a few little earthly connotations.


The galaxy was spotted by the James Webb Space Telescope, the newest and most powerful observatory in the world, which kicked off operations last week. The starlight that Webb spotted from this galaxy left its glittery boundaries long ago, before, well, nearly everything. 


According to two separate teams of astronomers, that blurry tomato we’re seeing is the way this galaxy looked just 300 million years after the universe came into existence. So, so much has happened since then—our sun flickered on, the planets were formed, life arose on Earth, Ring Pops were invented. Webb has rewound that tape. 


The glow of the most distant galaxies, the kind that the observatory was designed to detect, takes eons to reach us. When Webb captures this ancient, well-traveled light, the telescope becomes a time machine. So by gazing upon this red blob, we are looking back more than 13.5 billion years, at a cosmic memory.


Hello, Glassy (Tommaso Treu / Pascal Oesch / NASA / CSA / ESA / STScI)


Several astronomers I’ve spoken with say that the preliminary discovery, if it holds true, could have extraordinary implications for the next era of astronomy. Neither of the teams that spotted the cosmic tomato expected to find a galaxy like this so soon, in their very first observations of this kind. 


Astronomers haven’t even cranked up the Webb telescope as far as it can go; they’ve given it a little poke, and already distant galaxies like this one are “just falling off the tree,” Jane Rigby, a NASA astrophysicist and the Webb operations project scientist, told the Atlantic. 


Also the galaxy appeared in a tiny field of view, smaller than a crater on the moon in the night sky; who knows what else Webb will find in the entire moon’s worth of sky? With each deep observation, every big rewind, the telescope will bring us closer to the Big Bang, revealing faint galaxy after galaxy. We’re about to go rolling through time.


The new galaxy is still only a candidate for the title of most distant galaxy ever discovered. For one thing, the finding has yet to undergo peer review. For another, the astronomers who spotted the galaxy in the Webb data—two separate teams, working independently, one of which calls its find GLASS-z13 and the other GHZ2—will need to make new observations to confirm its distance. (I’ll call the galaxy Glassy to make things easier; the data set that produced the discovery is known as GLASS.) But if it’s confirmed, Glassy’s red glow would break the current record, set by a galaxy spotted through the Hubble Space Telescope in 2015, for the most ancient light ever observed by 100 million years or so.


The teams that found Glassy have dated it by studying the properties of its light. The universe has been expanding ever since the Big Bang, a process that stretches light into longer, redder wavelengths. Starlight from distant galaxies leaves its source as visible light, but by the time it reaches us, it is “redshifted” down the electromagnetic spectrum into the infrared range—invisible to our eyes, but perfect for Webb’s sensors. Astronomers know that the redder light is, the farther away the galaxy that produced it. 


Glassy “is detected very, very well in the redder wavelengths, but when you go to the bluer wavelengths, it just completely drops out, and it drops out very dramatically,” Rohan Naidu, an astronomer at Harvard who led one of the teams that spotted the galaxy, told me. “That signature is very characteristic of these very distant galaxies, and it’s very difficult for any other objects to make in such a dramatic manner.”


A zoomed-out view of Glassy (Tommaso Treu / NASA / CSA / ESA / STScI)


To confirm Glassy’s distance from us, astronomers will need to measure the galaxy’s light using a different method that would reveal information about its chemical composition. That technique is considered the gold standard in measuring galactic distances, and scientists are certain that Webb can pull it off. Last week, the Webb team released data that showed just how well the observatory can capture the particularities of a galaxy much closer than Glassy, but still considered quite distant. 


The light from that galaxy took 13.1 billion years to reach Earth, and yet Webb could pick out the distinct signatures of oxygen, hydrogen, and neon with impressive sharpness. Knowing the composition of the most distant galaxies “is really going to reveal to us something fundamental about how these galaxies form and grow,” Tommaso Treu, a UCLA astrophysicist and member of the other team that independently identified the galaxy, told me. (Treu also led the Webb observation program that produced the data in which Glassy was found.)


For now, astronomers are basking in the possibility of Glassy, which, on top of being a potential record-breaker, is also far weirder than they’d imagined. Astronomers have always thought that galaxies couldn’t have gotten very big so early in the universe’s history, and would start bulking up on stars about 500 million years out from the Big Bang. But Glassy is extremely luminous, suggesting that it holds an abundance of stars, which together are 1 billion times as massive as our sun. 


“That would mean that star formation gets going fast,” Chris Lintott, an Oxford astronomer who studies galaxy formation and was not involved in the new research, told me. Maybe producing massive stars is far easier than scientists have predicted, or perhaps the very earliest galaxies were shaped by gravitational forces we don’t understand. Whatever the explanation, the existence of galaxies such as Glassy would suggest that “the end of the universe’s dark ages”—when the first stars ignited—would have been “spectacular,” Lintott said.


This is just the beginning of getting closer to the beginning. Expect a flood of “now this might be the most distant galaxy we’ve ever seen!” scientific papers. Several astronomers told me that they would not be surprised if the next candidate for the title holder is announced as soon as next week. A year from now, they said, tens, maybe hundreds, of galaxies might be identified at similar distances. 


“We’ll figure out which ones are real, and then we’ll study those,” Rigby said. Then the true fun will begin—figuring out what those galaxies are made of, how much dust they contain, the story of the brilliant stars within. We’re only just starting to get familiar with the universe’s most ancient light, even though it’s been out there all along. “We have, for all of human history, been bathed in light reaching us from such distant galaxies, born when the universe was just a few hundred million years old,” Lintott said. “But only now have we built something capable of capturing it.”

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