It isn’t easy to build a galaxy. The universe is a good 13.8 billion years old and the earliest galaxies ever detected—spotted by the James Webb Space telescope last November—did not form until 350 million years after the Big Bang. Not only did that infant universe take its time bringing forth its first galactic masses, it also didn’t build very big ones once it got around to it. The first galaxies were often dwarf galaxies—containing perhaps 100 million stars—compared to the size of modern galaxies like our Milky Way, which is believed to contain a minimum of 100 billion stars. Early galaxies, so the rule goes, were pipsqueaks.
Or at least that’s what the rule used to be. According to a new paper published today in Nature, objects that are thought to be at least six galaxies dating back as far as 500 million years after the Big Bang have been discovered with populations of tens or even hundreds of billions of stars. The largest of the six is thought to have a collective mass one trillion times greater than our sun—or 10 times the size of the Milky Way.
“It’s bananas,” said Erica Nelson, an assistant professor of astrophysics at the University of Colorado, Boulder, and a co-author of the paper, in a statement that accompanied its release. “You just don’t expect the early universe to be able to organize itself that quickly. These galaxies should not have had time to form.”
The observations, conducted by the Webb telescope last summer, were of a patch of sky near the Big Dipper that had previously been imaged by the Hubble Space Telescope. Hubble had detected nothing special in that region of space, but Hubble sees principally in the visible spectrum, while Webb operates in the infrared—essentially bringing a completely fresh eye to an otherwise familiar piece of cosmic real estate.
Straightaway, the new survey yielded something intriguing: popping out from the otherwise unremarkable background image were six blotches of light which, though fuzzy, were extremely bright and extremely red. It was the color that caught the astronomers’ eyes first. The universe is continually expanding and as objects move away from us, their wavelength of light is stretched into the red spectrum. The redder the color, the farther the object. These half dozen objects were so red they were calculated to be far enough away to have formed up to 13.3 billion years ago. What’s more, they were big—big enough not to be point sources of light like a bright star or a supernova, but galactic in scale.
That initial estimate of size, however, could have been an illusion. As Albert Einstein first postulated, and as more than a century of observations have confirmed, light from a distant object in space can be bent by the gravity of foreground objects, causing it to appear larger than it is—a phenomenon known as gravitational lensing. It was entirely possible that the seemingly galactic scale objects the authors of the new paper discovered were actually much smaller than they appeared and were simply being optically magnified. That idea, however, was quickly dismissed. Closer scrutiny of the entire image revealed no foreground bodies near enough to the six bright objects to have distorted their shape or size.
That left galaxies as the likeliest explanation for what the objects are—though even the researchers admit it will take follow-up observations to confirm that fact. Still, the possibility that they are indeed galaxies raises as many questions as it answers. For one thing, the galaxies would have to have been explosively prolific. The Milky Way is thought to give birth to perhaps two new stars every year. For the six galaxies detected in the new observations to have gotten as big as they did as fast as they did, they’d have had to be forming hundreds of new stars a year for hundreds of millions of years. For another thing, in the early days of the universe, heavier elements found in modern stars weren’t around: the principal elements that formed stars were hydrogen and helium, and that made for relatively small galaxies. If ones this big formed so early, it would mean that heavier matter was indeed more plentiful and present than scientists thought.
“If even one of these galaxies is real,” Nelson said in a statement, “it will push against the limits of our understanding of cosmology.”
That “if” is a small word with big implications, and the area of the sky that is home to the new objects will surely be scoured by other observations. Currently, the Webb team receives about a thousand requests for telescope observing time per year from astronomers around the world and is able to approve only about 200 of the applications. Some of those studies are certain to include observations of the new bodies with the telescope’s near-infrared spectrograph (NIRSPEC), which analyzes the temperature, mass, and chemical composition of target objects. If the six candidate galaxies are indeed actual galaxies, NIRSPEC should confirm that fact. In the process, it will completely transform our current understanding of how quickly large and mature galaxies could evolve and form.
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Write to Jeffrey Kluger at email@example.com