James Webb Space Telescope spies most ancient galaxies ever observed
The James Webb Space Telescope (JWST) has clapped back at the oldest galaxies ever observed.
Astronomers are now certain that light from these galaxies has been traveling to Earth for more than 13.4 billion years, two new studies report. The results show that these galaxies inhabited the universe when it was less than 350 million years old and demonstrate the rapid emergence of the first generations of galaxies.
“It was crucial to prove that these galaxies do, indeed, reside in the early universe. It is quite possible that the nearest galaxies are masquerading as very distant galaxies,” Emma Curtis-Lake, a co-author of one of the new studies and an astronomer. at the University of Hertfordshire in England, says a statement (opens in new tab).
“Seeing the spectrum revealed as we hoped, confirming that these galaxies are at the true edge of our view, just a bit farther than Hubble could see! It’s an extremely exciting achievement for the mission,” said Curtis-Lake.
Related: James Webb Space Telescope: Everything you need to know
Diagram of spectroscopic results from the James Webb Space Telescope showing four early galaxies. (Image credit: NASA, ESA, CSA, M. Zamani (ESA/Webb), Leah Hustak (STScI), Brant Robertson (UC Santa Cruz), S. Tacchella (Cambridge), E. Curtis-Lake (UOH), S Carniani (Scuola Normale Superiore), JADES Collaboration)
The discovery confirms JWST’s ability to perform one of its most important tasks – studying the early universe through light that has traveled as long as the expansion of the universe has stretched its wavelength. This stretch of light is called redshift; the longer the light travels, the further toward the red end of the electromagnetic spectrum the expansion of the universe shifts its light. This means that redshift can be used as a measure of distance, and that early galaxies should have light that exhibits extreme redshifts, with their light extending into the infrared—JWST’s specialty.
So far, the $10 billion observatory has identified several candidate galaxies at extremely high redshift, but these observations must be confirmed using spectroscopy.
Spectroscopy can be used to distinguish between early galaxies and nearby, more contemporary galaxies that may share similar properties, because spectroscopy can distinguish the characteristic fingerprints of specific elements. Early galaxies consist mainly of hydrogen and helium, with no heavier elements such as oxygen, nitrogen and carbon. This is because they have not yet been enriched by the heavy elements forged from stars through nuclear fusion and then dispersed when these stars die and go supernova.
The researchers’ analysis of data collected by JWST’s Near-Infrared Camera (NIRCam) and Near-Infrared Spectrograph (NIRSpec) instrument allowed them to determine that the four galaxies identified JADES-GS-z10-0 , JADES-GS-z11-0. JADES-GS-z12–0 and JADES-GS-z13–0 have indeed extreme redshifts, from 10.3 to 13.2. (JADES, by the way, stands for “JWST Advanced Deep Extragalactic Survey.”)
They came to this conclusion because the spectra from these galaxies lack the telltale signature of heavy elements like carbon, meaning JWST is seeing them as they were when the universe was only 300 to 500 million years old. (The universe is currently about 13.8 billion years old.)
“For the first time, we have detected galaxies just 350 million years after the Big Bang and can be absolutely certain of their fantastic distances,” co-author and NIRCam science team member Brant Robertson said in the statement. “Finding these early galaxies in such stunningly beautiful images is a special experience.”
The observations come from the first round of JADES observations, which were aimed at a small area of the sky known as the Ultra Deep Field that has been probed for nearly two decades by the Hubble Space Telescope. This part of the sky contains about 100,000 galaxies, each captured at some point in its history, potentially billions of years in the past.
The researchers used over 10 days of JWST mission time to study the Ultra Deep Field with NIRCam, observing it in nine different infrared colors. This was followed by 28 hours of data collection performed by the NIRSpec instrument over three days. JWST therefore provided extremely sensitive and sharp images of the region and also provided astronomers with the data they needed to obtain a precise measurement of the redshift of each galaxy and to reveal the properties of the gas and stars within each.
“These results are the culmination of why the NIRCam and NIRSpec teams came together to run this observing program,” said NIRCam principal investigator Marcia Rieke of the University of Arizona.
The two papers were published today (April 4) in the journal Nature (opens in new tab). The researchers first reported the results in December 2022, when they presented them at a conference.
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