James Webb Reveals Candidate Oldest Galaxies, Sparking Debate on Universe‘s Beginnings
NASA‘s $10 billion James Webb Space Telescope (JWST) has delivered astonishing images of distant cosmic phenomena since beginning science operations in July 2022. But one of its most groundbreaking discoveries emerged in January 2023, when an international team announced the detection of four exceptionally ancient galaxy candidates.
These embryonic galaxies date back over 13 billion years, to when the universe was only a few hundred million years old. The findings provide new clues to that mysterious era after the Big Bang, when the first stars and galaxies formed. Yet some experts argue Webb may have misidentified the primeval objects, touching off lively discussion among cosmologists.
As the scientific community scrutinizes the data, Webb‘s glimpse into the extreme early universe highlights lingering questions about cosmic origins. The saga also demonstrates how radically the telescope can transform our comprehension of spacetime‘s distant past.
Illuminating Creation‘s ‘Dark Ages‘
Astronomers designate the phase shortly following the Big Bang as the "Dark Ages." During this window, which lasted several hundred million years, the primordial universe contained mostly neutral hydrogen and helium atoms, along with mysterious dark matter. There were no luminous objects emitting light.
The Dark Ages ended when gravity condensed the very first stars out of clouds of hydrogen and helium. The ignition of these colossal stars, and their explosion as supernovae, forged the first heavy elements like carbon, oxygen and nitrogen. Out of this enriched material, smaller stars and prototype galaxies took shape.
Observing the Cosmic Dawn when star formation initially began, and the subsequent emergence of early galaxies, could tremendously advance theories about the universe‘s evolution. "Theorists are very keen to see Webb constrain the first galaxies that formed after the Big Bang," says astronomer Emma Curtis-Lake of the University of Hertfordshire, a member of the JADES collaboration using Webb to study distant galaxies.
But peering so far across space and back in time pushes even Webb‘s capacities. It requires the instrument‘s unprecedented infrared sensitivity, which can detect extremely redshifted light from the farthest observable galaxies. As Curtis-Lake notes, "The limiting factor…is simply that these galaxies are very faint."
Four 13 Billion-Year-Old Galaxies?
The research team, including members of Webb‘s NIRSpec and NIRCam instrument teams, utilized both cameras to analyze a region called the Hubble Ultra Deep Field. This area, first imaged by Hubble in the mid-2000s, harbors some of the most distant galaxies viewable. Astronomers took the equivalent of a nine-to-twenty-eight hour long-exposure image, accumulating enough fragile light from remote sources to study them.
Through spectroscopy, the team pinpointed what they interpret as four exceptionally redshifted galaxies, denoting extreme distances (and ages) based on their wavelengths. If the redshift measurements prove accurate, these galaxies would have formed a mere 300 to 500 million years after the Big Bang, when the universe was only 3 to 5 percent its current age. That means Webb may have spotted some of cosmic history‘s very first galaxies.
"I was really excited to see such clear detections 12.8 to 13.6 billion years back in time," says astronomer Brant Robertson of UC Santa Cruz, another JADES team member. "The signals were unambiguous." The researchers named the objects after their redshifts (actually super-high blueshifts from our perspective): JADES-GS-z10-0, JADES-GS-z11-0, JADES-GS-z12-0 and JADES-GS-z13-0.
But another group of scientists quickly questioned the findings in their own paper published days later. They propose an alternative interpretation — that the observed objects are not ancient galaxies, but actually dark stars. These hypothetical objects, composed of normal matter and dark matter, could mimic the appearance and perceived distances of early galaxies. Resolving this debate awaits further observations by Webb and other instruments.
Improbable Images Require Epic Exposures
Regardless of their exact identity, recording measurable signals from sources potentially dating from only a few hundred million years after the Big Bang alone represents a monumental achievement. Gathering enough light to generate meaningful data demanded extraordinary efforts by the JADES program and Webb itself.
"You need a very big telescope to collect enough light from these faint early galaxies to understand their properties," Robertson emphasizes. "Their distances make them incredibly challenging targets." Even for Webb, the biggest telescope in space, photographing these realm-crossing galaxies strained the bounds of possibility.
The objects reside over 30 billion light years from Earth; because of cosmic expansion during the billions of years their light traveled here, they now lie around 40 billion light years away. But when the galaxies originally emitted the light, mere hundreds of millions of years had passed since cosmic creation. In a fundamental sense, because observing distant regions allows sight into correspondingly distant eras, astronomers stand witness through such images to the dawning of star and galaxy formation.
"What I find amazing is that Webb can capture light from so long ago," says astronomer Leah Hustak of the Space Telescope Science Institute, another project participant. "It‘s allowing us to directly observe the Cosmic Dawn and start to understand how early galaxies formed." Really comprehending these youthful galaxies requires obtaining information known as spectra — detailed readings of objects‘ light signatures across infrared wavelengths.
Spectra supply crucial insights like galaxies‘ chemical makeup, stellar populations, distances and ages. But gathering enough light for robust spectra again demanded extraordinary observing stamina from Webb. "The primary constraint in studying early galaxies is having sensitive enough instruments to detect their faint signals," Curtis-Lake explains.
The exposures ranged up to 28 hours for the oldest candidate galaxy. Even prolonging data collection to such extremes, spectra quality remains limited. "The objects are still only barely detected in these long exposures," notes Robertson. Still, the spectra did clearly exhibit telltale signatures of very distant galaxies. That includes intense emission from doubly-ionized oxygen, indicating stellar nurseries full of hot, massive stars.
And CONTRAST project leader Stephen Tacchella of Cambridge stresses how groundbreaking even fuzzy information is for investigating the universe‘s formative chapter. "Any insights at these extreme distances are exciting and give us clues into how galaxies form," Tacchella says. "These observations push Webb to its limits."
Debates and Discoveries from New Cosmic Frontiers
But rebuttals quickly materialized following January‘s ancient galaxy announcement. Only days afterward, astronomer Rennan Barkana of Tel Aviv University publicized a competing explanation. His paper, coauthored with colleagues from the University of Texas at Austin, instead interprets the objects as dark stars rather than galaxies.
These long-hypothesized bodies, composed of hydrogen, helium and dark matter, might dominate the early universe‘s first stages. They could potentially mimic both the observed cross-universe distances and chemical signatures of embryonic galaxies. "It‘s not impossible the four candidates are galaxies," acknowledges Texas coauthor Isaac Shivvers. "But the dark star scenario seems more likely."
The teams‘ differing conclusions highlight uncertainties in analyzing Webb‘s unprecedented deep space data. "When you point the most sensitive telescope ever constructed farther than anyone has looked before, you expect to be surprised," reasons Shivvers. Indeed, another recent paper suggests Webb may have already viewed a dark star. Clearly such intriguing entities, seemingly bobbing into view at observable existence‘s hazy frontiers, require examining with multiple approaches.
"Over the next year, we should be able to gather more data," says Curtis-Lake. "Hopefully that will help determine if these candidates are some of the earliest galaxies in the universe, or alternatively very distant dark stars." Additional pointings could also uncover even more primitive galaxy candidates, from deeper eras after the Bang. "There are likely galaxies at higher redshifts waiting to be confirmed," Robertson agrees.
Inaugurating new instruments like Webb invariably incites revolutions in comprehension. Gaining access to barely-glimpsed cosmic territories reshapes ideas, poses unforeseen questions, ignites vigorous debate. Discoveries shift understanding‘s very foundations in exciting, disruptive ways.
Studying the primordial universe‘s structure, contents and population comprises perhaps the highest-impact area that Webb could revolutionize over its multiyear mission. Even amidst ongoing analysis and arguments, the telescope‘s radical observations seem poised to completely transform conceptions of spacetime‘s formative phases. They herald a new portal onto cosmic creation itself.
