A Wave of Ancient Quasars from the Dawn of the Universe

Keck Observatory and ESA’s Euclid mission double the known population, including the two most distant quasars ever found

15 of the 31 quasars discovered, the small dots at the center of each tile, with their names and redshift (z). Credit: ESA/Euclid/Euclid Consortium/NASA, image processing by the Euclid Science Ground Segment and Antoine Basset (CNES).

Maunakea, Hawaiʻi — Astronomers using the W. M. Keck Observatory on Maunakea, Hawaiʻi Island, have confirmed two-thirds (21 of 31) of the most ancient quasars from the Euclid mission, including two of the most distant ever observed.

Quasars represent a brief phase in a galaxy’s life during which large amounts of material spiral into the central supermassive black hole, releasing enormous amounts of energy. In this phase, the galaxy’s nucleus can become one of the brightest persistent sources in the Universe.

Astronomers have been hunting for the Universe’s earliest quasars for decades. These celestial archives reveal conditions in the earliest days of the cosmos, including how the first supermassive black holes and galaxies took shape. But accessing them isn’t easy. Quasars from this era are difficult to find: they are elusive, as few galaxies had time to grow large enough, and their light has traveled for more than 13 billion years to reach us, arriving faint and stretched into infrared wavelengths, where it can resemble nearby cool stars.

“We see these quasars as they were during the Universe’s infancy,” says Daming Yang, lead author of the study and graduate student at Leiden University in the Netherlands. “By finding and studying them, we can better understand how these enormous systems formed and grew so quickly — one of the greatest mysteries in astrophysics.”

The study, led by an international team in the Euclid consortium, is published in today’s issue of Astronomy & Astrophysics.

Confirming Ancient Quasars

The 31 quasars reported here were selected from ESA’s Euclid Wide Survey, which will cover more than one-third of the total sky once complete. While the Euclid mission identified promising candidates, confirming them required follow-up spectroscopy from ground-based observatories.

To confirm these quasars spanning redshifts from 6.5 and beyond, the team used three instruments at Keck Observatory, covering a broad wavelength range: the Multi-Object Spectrograph for Infrared Exploration (MOSFIRE), the Low Resolution Imaging Spectrometer (LRIS), and the Keck Cosmic Web Imager (KCWI). With these instruments, the team analyzed the light from more than 100 candidates in the northern sky, searching each one for a telltale signature: a sharp drop in brightness known as the Lyman-alpha break. This cutoff is imprinted by hydrogen gas that pervaded the early universe, which absorbed the quasar’s light at specific wavelengths before it could reach us. The precise location of that drop confirms the object as a genuine quasar and pins down its distance.

The challenge is that these quasars appear incredibly faint due to their extreme distances, so detecting this signal requires the combination of highly sensitive instruments and the light-gathering capability of the world’s largest ground-based telescopes, such as Keck Observatory.

An elusive and distant population

Before Euclid, astronomers had identified only a handful of quasars at redshift 7 or higher after decades of searching — a measure of distance tied to how light stretches as the universe expands — corresponding to the first 770 million years after the Big Bang. Finding more and pushing further into the early universe is extraordinarily challenging for several reasons: so early in cosmic history, very few galaxies had grown large enough to power them; those that existed are so far away that their light has been travelling for over 13 billion years, arriving incredibly dim; and over that vast journey, the light has been stretched into infrared wavelengths, invisible to traditional optical telescopes.

The mission has already uncovered 12 new quasars above redshift 7, more than doubling the known population. For the first time, astronomers have a large enough sample to study these ancient quasars not as individual curiosities but as a population, building the first statistical picture of how supermassive black holes formed and grew in the Universe’s earliest epochs.

The two most ancient of the batch, EUCL J172902.75+641018.1 and EUCL J125308.55+705432.3, have redshifts of 7.77 and 7.69, respectively, setting a new record for the most ancient quasars ever found. Both lie more than 13 billion light-years away and emerged during the Universe’s first 670 million years.

Building a quasar chronicle

A multi-wavelength follow-up study of all high redshift quasars is currently underway. Using a collection of ground and space-based telescopes the team is constructing a quasar chronicle that will trace how supermassive black holes and their host galaxies evolved over the first billion years of cosmic history, and how reionization unfolded.

“We have a real sample at such high redshift for the first time, and we can finally start answering the questions that were unanswerable before,” said Yang.

“Every one of these 31 quasars is a new sightline into the early Universe, and the follow up science is just beginning” added Joseph Hennawi, co-author and professor at the University of California, Santa Barbara.

As the ESA Euclid space telescope continues to scan new sky, the probability of finding the first quasars beyond redshift 8 increases. A redshift 8 quasar would be shining when the Universe was less than about 630 million years old and would also place the strongest direct constraints yet on how early supermassive black holes could have formed and grown.

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ABOUT MOSFIRE The Multi-Object Spectrograph for Infrared Exploration (MOSFIRE), gathers thousands of spectra from objects spanning a variety of distances, environments and physical conditions. What makes this large, vacuum-cryogenic instrument unique is its ability to select up to 46 individual objects in the field of view and then record the infrared spectrum of all 46 objects simultaneously. When a new field is selected, a robotic mechanism inside the vacuum chamber reconfigures the distribution of tiny slits in the focal plane in under six minutes. Eight years in the making with First Light in 2012, MOSFIRE’s early performance results range from the discovery of ultra-cool, nearby substellar mass objects, to the detection of oxygen in young galaxies only two billion years after the Big Bang. MOSFIRE was made possible by funding provided by the National Science Foundation.

ABOUT KCWI The Keck Cosmic Web Imager (KCWI) is designed to provide visible band, integral field spectroscopy with moderate to high spectral resolution formats and excellent sky-subtraction. The astronomical seeing and large aperture of the telescope enables studies of the connection between galaxies and the gas in their dark matter halos, stellar relics, star clusters, and lensed galaxies. KCWI covers the blue side of the visible spectrum; the instrument also features the Keck Cosmic Reionization Mapper (KCRM), extending KCWI’s coverage to the red side of the visible spectrum. The combination of KCWI-blue and KCRM provides simultaneous high-efficiency spectral coverage across the entire visible spectrum. Support for KCWI was provided by the National Science Foundation, Heising-Simons Foundation, and Mt. Cuba Astronomical Foundation. Support for KCRM was provided by the National Science Foundation and Mt. Cuba Astronomical Foundation.

ABOUT LRIS The Low Resolution Imaging Spectrometer (LRIS) is a very versatile and ultra-sensitive visible-wavelength imager and spectrograph built at the California Institute of Technology by a team led by Prof. Bev Oke and Prof. Judy Cohen and commissioned in 1993. Since then it has seen two major upgrades to further enhance its capabilities: the addition of a second, blue arm optimized for shorter wavelengths of light and the installation of detectors that are much more sensitive at the longest (red) wavelengths. Each arm is optimized for the wavelengths it covers. This large range of wavelength coverage, combined with the instrument’s high sensitivity, allows the study of everything from comets (which have interesting features in the ultraviolet part of the spectrum), to the blue light from star formation, to the red light of very distant objects. LRIS also records the spectra of up to 50 objects simultaneously, especially useful for studies of clusters of galaxies in the most distant reaches, and earliest times, of the universe. LRIS was used in observing distant supernovae by astronomers who received the Nobel Prize in Physics in 2011 for research determining that the universe was speeding up in its expansion.

ABOUT KECK OBSERVATORY The W. M. Keck Observatory telescopes are among the most scientifically productive on Earth. The two 10-meter optical/infrared telescopes atop Maunakea on the Island of Hawaiʻi feature a suite of advanced instruments including imagers, multi-object spectrographs, high-resolution spectrographs, integral-field spectrometers, and world-leading laser guide star adaptive optics systems. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c) 3 non-profit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. For more information, visit: www.keckobservatory.org

Originally published at https://keckobservatory.org on July 6, 2026.