The Webb telescope has unleashed a torrent of scientific discovery since becoming operational last year, peering farther than ever before into the universe's distant reaches — which also means it is looking back in time.

By the time light from the most distant galaxies reaches Earth, it has been stretched by the expansion of the universe and shifted to the infrared region of the light spectrum.

The Webb telescope's NIRCam instrument has an unprecedented ability to detect this infrared light, allowing it to quickly spot a range of never-before-seen galaxies — some of which could reshape astronomers' understanding of the early universe.

In two studies published in the Nature Astronomy journal, astronomers revealed they have "unambiguously detected" the four most distant galaxies ever observed.

The galaxies date from 300 to 500 million years after the Big Bang more than 13 billion years ago, when the universe was just two percent of its current age.

That means the galaxies are from what is called "the epoch of reionization," a period when the first stars are believed to have emerged. The epoch came directly after the cosmic dark ages brought about by the Big Bang.

 

'Surprising'

Stephane Charlot, a researcher at the Astrophysics Institute of Paris and co-author of the two new studies, told AFP that the farthest galaxy — called JADES-GS-z13-0 — formed 320 million years after the Big Bang.

That is the greatest distance ever observed by astronomers, he said.

The Webb telescope also confirmed the existence of JADES-GS-z10-0, which dates from 450 million years after the Big Bang and had previously been spotted by the Hubble Space Telescope.

All four galaxies are "very low in mass," weighing roughly a hundred million solar masses, Charlot said. The Milky Way, in comparison, weighs 1.5 trillion solar masses by some estimations.

But the galaxies are "very active in star formation in proportion to their mass," Charlot said.

Those stars were forming "at around the same rate as the Milky Way," a speed that was "surprising so early in the Universe," he added.

The galaxies were also "very poor in metals," he added.

This is consistent with the standard model of cosmology, science's best understanding of how the universe works, which says that the closer to the Big Bang, the less time there is for such metals to form.

 

Technical tour de force'

However, in February, the discovery of six massive galaxies from 500-700 million years after the Big Bang led some astronomers to question the standard model.

Those galaxies, also observed by the Webb telescope, were bigger than thought possible so soon after the birth of the universe — if confirmed, the standard model could need updating.

Pieter van Dokkum, an astronomer at Yale University not involved in the latest research, hailed the confirmation of the four newly discovered distant galaxies as a "technical tour de force".

"The frontier is moving almost every month," van Dokkum commented in Nature, adding that there was now "only 300 million years of unexplored history of the universe between these galaxies and the Big Bang".

The Webb telescope has observed possible galaxies even closer to the Big Bang, but they have yet to be confirmed, he said.   

 

Rocky exoplanet

In a separate development, the James Webb Space Telescope has measured the temperature of a rocky exoplanet for the first time, finding that a "cousin" of Earth most likely lacks an atmosphere, researchers said on March 27.

When the Trappist-1 system was discovered in 2017, astronomers were excited at the prospect that some of its seven rocky planets — which are roughly similar to Earth in size and mass — could be habitable.

Just 40 light years from Earth, the planets orbit much closer to their ultracool red dwarf star than the rocky planets in our Solar System. But their star gives off far less energy than our Sun.

The system made an obvious target for the piercing gaze of the Webb telescope, which has unleashed a torrent of scientific discovery since releasing its first observations in July.

Astronomers focused on Trappist-1b, the closest planet to the red dwarf, because it was the easiest to spot.

Webb's Mid-Infrared Instrument (MIRI) measured the change in brightness when the planet moved behind its star, in what is known as a secondary eclipse.

"Just before disappearing behind the star, the planet gives off the most light because it almost exclusively shows its 'day' side," Elsa Ducrot, a coauthor of a new study published in the journal Nature, told AFP.

By subtracting the brightness of the star, the researchers calculated how much infrared light the planet was giving off.

The MIRI instrument was therefore able to act like "a giant touch-free thermometer," NASA said in a statement.

 

'Perfect for baking pizza'

The planet's dayside temperature was determined to be 230 degrees Celsius — "just about perfect for baking pizza," NASA added.

France's Atomic Energy Commission (CEA) said that the heat was not redistributed throughout this "cousin" of Earth, a role normally provided by an atmosphere.

The scientists therefore concluded that Trappist-1b "has little or no atmosphere," said Ducrot, a CEA astrophysicist. She emphasized that other wavelengths would need to be analyzed to confirm the result.

But it was certain that the atmosphere did not contain carbon dioxide, because that would have absorbed some of the light, she added.

The Spitzer Space Telescope was not able to rule out an atmosphere on Trappist-1b despite observing 28 secondary eclipses, Ducrot said.

"The James Webb saw it in a single eclipse!"

The ability to analyze the potential atmospheres of such rocky exoplanets opens "a new era" in the study of planets outside our Solar System, she added.

It was already known that Trappist-1b was uninhabitable, as it is too close to its star.

But Trappist-1e, Trappist-1f and Trappist-1g are all thought to be in what is called the "goldilocks zone".

Planets in this zone have a moderate temperature which could support liquid water — considered essential for life anywhere.