Webb Telescope Reveals Unexpected Bounty of Bright Galaxies in the Early Universe | science

The James Webb Space Telescope has only been observing the sky for a few weeks, and already it has made a surprising discovery: tens, hundreds, maybe even 1000 times more bright galaxies in the early universe than astronomers predicted.

“No one expected anything like this,” says Michael Boylan-Kolchin of the University of Texas, Austin. “Galaxies are bursting out of the woodwork,” says Rachel Somerville of the Flatiron Institute.

Galaxy formation models may now need revision, as current ones argue that gas clouds should be much slower to coalesce into stars and galaxies than suggested by Webb’s galaxy-rich images of the universe early, less than 500 million years after the big bang. “This is very outside the box of what the models predict,” says Garth Illingworth of the University of California (UC), Santa Cruz.

Webb, an orbiting observatory run by NASA with contributions from the European and Canadian space agencies, began observing in late June from its vantage point 1.5 million kilometers from Earth. So far, much of its time has been devoted to projects aimed at showing off its capabilities, such as the Cosmic Evolution Early Release Science Survey (CEERS). Webb is designed to go deeper into cosmic history than its predecessor, the Hubble Space Telescope. Its 6.5-meter mirror, with six times the area of ​​Hubble, can pick up more light from distant sources and, unlike Hubble, operates at infrared wavelengths, making Webb more sensitive to those distant sources , whose light is stretched to longer and redder wavelengths by cosmic expansion.

Just days after Webb began observations, it spotted a candidate galaxy that appears to have been bright when the universe was only 230 million years old, 1.7% of its current age, which would make it the most far away never seen Surveys since then have shown the object to be just one of an impressive profusion of early galaxies, each small by today’s standards but brighter than astronomers expected.

Some researchers warn that the abundance, based on images of a small patch of sky, may be an illusion. Boylan-Kolchin wonders if Webb just got “extra lucky” and looked into a huge cluster of galaxies, denser than the rest of the early universe. That question will be resolved when CEERS expands its reach later this year and results come in from other large-scale surveys.

It is also possible for astronomers to misidentify galaxies from slightly more recent ages as very early galaxies. Spectra are the gold standard for measuring the age of a galaxy because they allow precise measurements of the reddening of its light. But gathering spectra from many galaxies takes time. Instead, Webb’s surveys so far have estimated the ages of galaxies from the color they appear in the images, a relatively crude method. Webb’s near-infrared camera filters its light into a few broad wavelength bins, giving astronomers a rough measure of color; redder equals farther. But dust surrounding a galaxy can fool observers, as it can absorb starlight and re-emit it at longer wavelengths, making the galaxy appear redder.

Webb’s early science teams have already identified some masked galaxies, as they report in several recent preprints. But if the profusion of early galaxies is real, astronomers may have to fundamentally rethink galaxy formation or the prevailing cosmology.

By looking at nearby galaxies, the researchers concluded that the heat inside the gas clouds slows down how quickly gravity would condense matter into stars, making star formation take about 100 times longer than if gravity alone charge As the first stars in a protogalaxy begin to shine, they inject more heat into the gas, pumping the brakes on star formation. And the first stars are short-lived giants; when they explode as supernovae, they heat the gas clouds even more or remove them entirely from a forming galaxy.

Studies with Hubble have shown that the rate of star formation has been relatively constant since about 600 million years after the big bang, says Charlotte Mason of the Niels Bohr Institute. But Webb’s results imply that in earlier times their pace was much faster — so fast, Somerville suggests, as if gas clouds were collapsing freely, without any slowing down from heat or supernovae.

In fact, Tommaso Treu of UC Los Angeles, who leads another Webb survey called GLASS, says his team is seeing these early galaxies “form stars like crazy.” They look, he adds, “like giant balls of star formation and nothing else.”

Theorists do not know whether the higher density of matter and higher temperatures of the early universe could have accelerated star formation. Another theory is that the first stars may have formed more quickly because they took shape only from the primordial matter left over from the big bang—hydrogen and helium—without the heavier elements forged by later generations of stars.

Or something may be wrong with the current understanding of how the universe evolves. The prevailing theory of cosmology, known as lambda-CDM (referring to cold dark matter), describes how, shortly after the big bang, the invisible dark matter that makes up most of the stuff in the universe clustered under its own gravity in “halos”. These halos drew on normal matter and created the conditions for it to condense into galaxies. Lambda-CDM predicts the number and size of haloes that should exist in the early universe, and thus the number of galaxies. “There’s not a lot of wiggle room,” says Boylan-Kolchin.

Somerville says it may be possible to tweak lambda-CDM to create something closer to what Webb is seeing. Or, he says, cosmologists may be forced to reassess the earliest moments of the big bang itself: the era of inflation, a period of rapid growth when quantum fluctuations grew into areas of higher or lower matter density: the seeds of the later halos. “If inflation is bad, that could be very fundamental,” he says. “But I wouldn’t bet on it being that.”

Having revealed the problem of early galaxies, Webb can provide the data needed to answer it. So far, Webb sees only young, hot, bright stars in new, early galaxies. Follow-up observations of these galaxies at longer wavelengths with Webb’s infrared instrument or ground-based radio telescopes sensitive to submillimeter waves could reveal that the gas clouds are actively building stars. These observations could help astronomers confirm that the first galaxies were unusually prodigious star factories and provide clues as to how they did so.

“We’ll have a much better picture of all this in 6 months,” says Boylan-Kolchin. “It’s a very exciting time.”

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