An international team of astronomers, including a team at the University of Arizona Steward Observatory , announced the discovery of 31 quasars from a time when the universe was just 600 to 800 million years old – a mere 5% of its current age. Quasars are among the brightest, most energetic objects in the universe, powered by supermassive black holes devouring matter at the center of galaxies.
The observations, published in the journal Astronomy & Astrophysics on July 6, mark a significant step forward in our understanding of the early universe and include the two most distant quasars ever observed. The bounty includes the new record-holder, designated as EUCL J172902.75+641018.1, corresponding to a cosmic age of about 670 million years and surpassing the previous record by 15 million years.
Their extreme luminosity makes quasars visible across cosmic distances, acting as beacons that illuminate the epoch of reionization, a pivotal phase when the first stars and galaxies ionized the dark, neutral hydrogen fog filling the early universe. Yet, quasars from that time period are exceedingly rare and difficult to detect. Their light is stretched into the near-infrared spectrum by cosmic expansion – hence the term "redshift" – falling into a wavelength range where Earth's atmosphere glows brightly, drowning out faint signals. Until now, only nine quasars had been confirmed at distances greater than "redshift seven" – meaning the light from those objects took nearly 13 billion years to reach Earth. Now, that number has grown to 23.
Scientists are still not sure how supermassive black holes containing the mass of billions of suns could form in the – cosmically speaking – short span of a few hundred million years after the Big Bang. Similarly, it is unclear how they influenced the reionization of the universe, what their host galaxies looked like and how the black holes affected them.
"With only a few quasars known beyond redshift seven, we simply cannot answer these questions," said Daming Yang, a doctoral student at Leiden Observatory and first author of the paper. "Finding more of them at such distances – and pushing to even greater distances – is the only way forward."
The Euclid Consortium scientists employed a multi-pronged approach. First, machine learning algorithms analyzed Euclid's optical and near-infrared band images, identifying candidates with the telltale dropout signatures in spectra of high-redshift quasars. Spectroscopic confirmation was obtained thanks to a ground-based follow-up with Keck Observatory in Hawaii, the Magellan Telescopes in Chile and the Large Binocular Telescope in Southern Arizona, headquartered at the University of Arizona, that confirmed 31 quasars from the early universe.
"The quasars presented in this paper are fainter, less luminous, and have somewhat lower-mass black holes than the ones that we discovered before," said Xiaohui Fan, Regents Professor of Astronomy at the U of A Steward Observatory. "Having a space telescope like Euclid dedicated to this purpose allows us to hunt for the smaller, less luminous ones that we weren't able to go after before."
Fan's team was instrumental in providing follow-up observations of selected targets that the survey turned up, taking advantage of the U of A's large telescopes to take long exposures of faint objects and analyze their spectra, like a "light-signature." Fan's colleagues at the U of A also measured the distances of early quasar candidates.
"This is truly exciting," said Jinyi Yang, a former assistant research professor at Steward, who is now an assistant professor at University of Michigan. "These luminous quasars, shining from deep within the reionization era, the last major transition in our universe's history, offer invaluable insights into how the cosmos emerged from darkness and how the earliest supermassive black holes formed."
The Euclid Space Telescope, launched in 2023, is transforming quasar discovery with its unprecedented combination of depth and sky coverage. Unlike previous surveys, Euclid's Near-Infrared Spectrometer and Photometer and Visible Camera scan thousands of square degrees with exquisite sensitivity. Reaching magnitudes as faint as 24.5 in the near-infrared, Euclid's data is deep enough to detect quasars 10 to 100 times fainter than those found in earlier wide-field surveys, allowing the elaboration of a wider and more representative catalogue of quasars from this epoch of the universe.
"We are reaching the limit of what ground-based observations can give us," Fan said. "We have to go really deep and cover a lot of sky, because these things are rare. Euclid allows us to find them, but to obtain the high spectroscopic resolution, we have to turn to our ground-based observatories like LBT and Magellan."
With only one year and a half of Euclid data, this discovery is just the beginning. The full 6-year survey is expected to uncover hundreds more high-redshift quasars, including the first z > 8 quasars.
"Discovery is only the first step," said Silvia Belladitta, postdoctoral researcher at the Max Planck Institute for Astronomy in Germany and lead author of a first follow-up paper to be published soon. "Observing these objects across the full electromagnetic spectrum using data from other facilities allows us to characterize the environments of these quasars and their host galaxies. Further observations on the second most ancient quasar showed that it is embedded in a dusty, gas-filled galaxy that is rapidly forming new stars, hinting at what the host galaxy of an early supermassive black hole may be like!"
The next Euclid data release is scheduled for late 2026. This unprecedented dataset, corresponding to one year of Euclid observations, will represent – and by far – the largest map of the universe ever produced from space in both infrared and visible light. Its unique combination of wide sky coverage and high resolution will also drive breakthroughs in many other fields of astrophysics, with discoveries on the nature of dark matter and dark energy expected in 2027.
The Euclid Consortium, in partnership with NASA and the European Space Agency, or ESA, designed and built the instruments of the Euclid space telescope. The Euclid mission aims to map the extragalactic sky over a period of six years, providing unique data that offer new insights into dark energy and dark matter. Launched on July 1, 2023, the telescope successfully began its cosmological survey on February 14, 2024. The Euclid Consortium comprises more than 2,000 members from more than 300 laboratories in 15 European countries, plus Canada, Japan and the United States, covering various fields in astrophysics, cosmology, theoretical physics and particle physics.
