Discovery of a Galaxy at Redshift 14.4, 280-Million Years After the Big-Bang
On January 15, 2013, I published a comprehensive textbook with my former PhD student, Steve Furlanetto (currently a tenured professor at UCLA), titled: “The First Galaxies in the Universe” (available here at Princeton University Press). The purpose of the textbook (and its shorter predecessor “How Did the First Stars and Galaxies Form?”, published three years earlier here), was to summarize the theoretical framework that I developed with my students and postdocs regarding the properties of the first stars and galaxies. These sources of ultraviolet light broke the primordial hydrogen atoms throughout the Universe into their constituent electrons and protons, ushering in the so-called Epoch of Reionization. The first light emitted by the earliest stars provide quantitative details to the scientific version of the biblical phrase in genesis: “Let there be light.” Understanding the formation of the first galaxies, which led to the production of the oxygen and carbon that biology relies on, is an important part of figuring out our cosmic roots. My textbook was written in anticipation of the James Webb Space Telescope, which I helped design as a member of its first working group two decades earlier.
After a major unexpected delay, the Webb telescope was finally launched in 2021 and operated magnificently as a discovery machine of the first galaxies since then.
In 1992, my colleague Piero Madau told me that his paper on high-redshift galaxies was rejected from publication by a referee who argued that the paper is too speculative because we do not know whether there are any galaxies whatsoever beyond redshift 2. The cosmic reality is very different than this referee conceived it to be. In fact, the Webb telescope has revealed a growing population of bright galaxies at redshifts larger than 10.
Yesterday, 13 years after my textbook was published, NASA announced here the confirmed detection of the record breaking farthest known galaxy, MoM-z14, in the COSMOS Legacy Field. This field covers a mosaic of the sky measuring 2 square degrees, about ten times the angular area of the Moon. The galaxy’s redshift is 14.44 (+/- 0.02), corresponding to about 280 million years after the Big-Bang, when the age of the infant Universe was only 2% of its current value, 13.8 billion years. The Universe expanded by a factor of 15.44 since this galaxy emitted its light and so the observed wavelengths of its radiation are stretched by this factor relative to their values at emission. The discovery, led by Rohan Naidu from MIT (who received his PhD from the Harvard Astronomy department in 2022) was announced 8 months ago in a preprint available here.
The redshift of MoM-z14 is confirmed spectroscopically with the NIRSpec/prism (Near-Infrared Spectrograph) through the detection of a sharp absorption break (owing to Lyman-alpha transition from the ground level to the first excited level of hydrogen atoms) as well as five ultraviolet emission lines including a nitrogen feature. These prominent ultraviolet lines signal a rising star-formation history, with a factor of 10 increase in the last 5 million years. As expected in my textbook for galaxies at that redshift, the source is extremely compact, about 240 light years in radius — a hundred times smaller than the separation between the Sun and the center of the Milky-Way galaxy.
The nitrogen spectral features observed in the early galaxy MoM-z14 cannot be produced by normal stars within 280 million years after the Big Bang. In a new research project that I am conducting with my postdoc, Devesh Nandel, we are relating the nitrogen production to supermassive stars which could have naturally formed out of the pristine cosmic gas before it was enriched with heavy elements by later generations of stars. As discussed in my textbook, the primordial hydrogen and helium gas could not cool efficiently and likely fragmented into massive stars.
The absence of a strong damping wing of the hydrogen absorption feature suggests that the hydrogen atoms in the immediate intergalactic environment of MoM-z14 were already broken, as expected in reionization models for that redshift. The galaxy MoM-z14 cleared out the thick, primordial hydrogen fog of the early Universe in the space surrounding it. Thus, MoM-z14 provides another clue for mapping out the timeline of reionization, work that was not possible until the Webb telescope lifted the veil on this cosmic era. Future radio observatories will aim to measure the faint emission by hydrogen from that era at a wavelength of 21-centimeter, as anticipated in my textbook.
Observing the earliest stars is akin to archaeology, since digging deep into space takes us back in time as a result of the finite speed of light. The Webb telescope is akin to an archeological shovel that reveals ancient layers of cosmic history.
Like other galaxies that the Webb telescope has discovered in the early universe, MoM-z14 is brighter and more chemically enriched than my textbook expected to find in this early era.
MoM-z14 is one of a growing group of surprisingly bright galaxies in the early Universe, about a hundred times more abundant than predicted in my textbook before the launch of the Webb telescope. When asked by reporters about my textbook 13 years ago, I expressed the hope that some of my predictions will be proven wrong by the Webb telescope. After all, science is a learning experience and observations are crucial in refining our ideas about our cosmic roots.
ABOUT THE AUTHOR
Avi Loeb is the head of the Galileo Project, founding director of Harvard University’s — Black Hole Initiative, director of the Institute for Theory and Computation at the Harvard-Smithsonian Center for Astrophysics, and the former chair of the astronomy department at Harvard University (2011–2020). He is a former member of the President’s Council of Advisors on Science and Technology and a former chair of the Board on Physics and Astronomy of the National Academies. He is the bestselling author of “Extraterrestrial: The First Sign of Intelligent Life Beyond Earth” and a co-author of the textbook “Life in the Cosmos”, both published in 2021. The paperback edition of his new book, titled “Interstellar”, was published in August 2024.
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