Euclid’s expanding quasar census is revealing how enormous black holes emerged during the Universe’s infancy.
More than 13 billion years ago, two brilliant objects blazed from galaxies that had barely begun to take shape. Their light, produced when the Universe was only 670 million years old, has now reached the European Space Agency’s Euclid space telescope.
The two objects are quasars, intensely bright galactic centers powered by supermassive black holes consuming surrounding matter. Each radiated with the power of roughly a trillion Suns when the cosmos was just 5% of its present age. They are the earliest quasars yet observed and belong to a group of 31 ancient quasars newly identified by Euclid.
A quasar appears during a relatively short period in a galaxy’s development. Gas and other material spiral toward the supermassive black hole at its center, forming a hot, rapidly moving disk that releases enormous amounts of energy. The resulting glow can be hundreds or thousands of times brighter than all the galaxy’s stars combined.
Astronomers have searched for the first quasars for decades because they preserve evidence from a formative period in cosmic history. Finding them could help explain how galaxies and supermassive black holes became so large so soon after the Universe began.
The search is difficult because these early objects are uncommon. Few galaxies had enough time to grow massive black holes, and the light reaching Earth is extremely faint after traveling across more than 13 billion light-years. Its appearance can also resemble that of much closer stars, making ancient quasars easy to overlook.
Euclid expands the quasar census
Euclid was launched in 2023 with the ability to examine broad areas of the sky while detecting faint infrared light. That combination allowed it to search efficiently through a period of cosmic history that earlier surveys could explore only in fragments.
The telescope has now identified 31 previously unknown quasars from the early Universe. The sample reaches back to a time when the cosmos had completed only 5% of its present lifespan.
“These early quasars date back to the Universe’s infancy,” says Daming Yang of Leiden University in the Netherlands, lead author of the Euclid discovery paper. “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.”
Earlier searches mostly detected the brightest and rarest quasars because those were easiest to distinguish at enormous distances. That left astronomers with too few examples to determine what the wider population looked like.
Euclid changes the investigation by detecting fainter objects across much larger regions of sky. Instead of studying only exceptional quasars, astronomers can begin examining a more representative group and asking how common these systems were during the Universe’s earliest stages.
“Euclid is a true game-changer,” adds Daming. “Before, we could only find a handful of the very brightest ancient quasars, but Euclid lets us search far more efficiently across huge areas of sky to capture much fainter light. It’s a unique tool for quasar hunting.”
Two quasars set new records
Among the discoveries are 12 quasars with a redshift of 7 or higher. Redshift describes how the expansion of the Universe stretches light toward longer, redder wavelengths. The greater the redshift, the farther back in time astronomers are looking. A value of 7 or above corresponds to the Universe’s first 770 million years.
The oldest objects in the group are EUCL J172902.75+641018.1 and EUCL J125308.55+705432.3. Their redshifts are 7.77 and 7.69, respectively, making them the earliest quasars currently known. Both are located slightly more than 13 billion light-years away and were already shining within the first 670 million years of cosmic history.
“This finding more than doubles the number of quasars we know of that are so ancient,” says Antonio La Marca, an ESA Research Fellow in the Euclid team. Astronomers needed more than a decade to locate the first 10 or so quasars with redshifts of 7 or higher. Euclid surpassed that total during a single year of observations.
“The Euclid team has taken a true ‘census’ of quasars at the dawn of the Universe for the first time,” adds Antonio. “It’s a big step toward understanding these fascinating objects on a more fundamental level.”
Quasars illuminate cosmic dawn
Silvia Belladitta and collaborators recently examined the second oldest quasar in greater detail. Their observations placed it inside a galaxy rich in gas and dust where stars were forming at an intense rate.
That environment offers a clue to how an early supermassive black hole and its host galaxy may have grown together. The black hole required a large supply of material to power the quasar, while the surrounding galaxy was simultaneously converting gas into new stars.
These objects appeared during the epoch of reionization, a major transition in cosmic history. Before this period, the Universe had passed through the ‘dark ages,’ when much of its hydrogen existed as cold, neutral gas. Energetic light from early stars, galaxies and quasars eventually ionized that gas, meaning it stripped electrons away from atoms (split apart by energetic light). This transformation helped create the transparent, structured cosmos observed today.
“Ancient quasars are rare discoveries. They’re interesting in themselves, but also time machines that enable us to explore the early Universe and understand how the first generation of galaxies came to be,” says ESA Euclid Project Scientist Valeria Pettorino.
A wider survey awaits
“Euclid’s capabilities are unrivaled. The telescope combines a large area, depth, sharp imaging, and unique space-based infrared vision in a way that lets us pick out rare, extremely distant objects far more efficiently than before.
And it’s not just the telescope: the data processing is only possible thanks to thousands of Euclid Consortium scientists and engineers working together to deliver scientific discoveries, sifting through enormous datasets to identify rare, distant quasars that we can study further using telescopes on the ground.”
The 31 quasars emerged from the Euclid Wide Survey, which will eventually examine more than one-third of the sky. As Euclid maps billions of galaxies, it is expected to uncover additional quasars alongside evidence about the composition, history, evolution and large-scale structure of the dark Universe.
References:
“Euclid: Discovery of 31 new quasars at 6.6 < z < 7.8” by D. Yang, J. F. Hennawi, F. Guarneri, J. Wolf, S. Belladitta, J.-T. Schindler, A. C. N. Hughes, E. Bañados, D. J. Mortlock, J. Yang, F. Wang, X. Fan, K. Jahnke, D. Stern, C. J. Willott, A. J. Barth, H. J. A. Rottgering, R. G. Varadaraj, R. Decarli, A.-C. Eilers, M. Ezziati, Y. Fu, J. Huang, X. Jin, Y. Kang, L. N. Martinez-Ramirez, Y. Matsuoka, M. Onoue, R. Pello, R. P. Remigio, W. L. Tee, B. Venemans, G. Vietri, B. Wang, L. J. Abbo, H. Atek, S. Bisogni, S. E. I. Bosman, R. A. A. Bowler, C. J. Conselice, F. B. Davies, C. M. Gutierrez, Y. Harikane, K. Rubinur, C. C. Lovell, M. Magliocchetti, J. Matthee, F. Ricci, M. Scialpi, D. Scott, L. Spinoglio, F. Tarsitano, Y. Toba, F. Walter, J. R. Weaver, G. Zamorani, B. Altieri, A. Amara, S. Andreon, H. Aussel, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, E. Branchini, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Cropper, J.-C. Cuillandre, H. Degaudenzi, G. De Lucia, C. Dolding, H. Dole, M. Douspis, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, R. Farinelli, S. Ferriol, F. Finelli, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, P. Gómez-Alvarez, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. Gwyn, S. V. H. Haugan, H. Hoekstra, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, M. Jhabvala, S. Kermiche, B. Kubik, K. Kuijken, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, H. J. McCracken, E. Medinaceli, S. Mei, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, J. J. Mohr, A. Mora, M. Moresco, L. Moscardini, E. Munari, R. Nakajima, C. Neissner, R. C. Nichol, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, G. D. Racca, F. Raison, R. Rebolo, A. Renzi, J. Rhodes, G. Riccio, H.-W. Rix, E. Romelli, M. Roncarelli, C. Rosset, B. Rusholme, R. Saglia, Z. Sakr, D. Sapone, M. Sauvage, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, S. Serrano, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, L. Stanco, J. Steinwagner, P. Tallada-Crespí, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, F. M. Zerbi, E. Zucca, G. Fabbian, M. Huertas-Company, J. Martín-Fleitas, P. Monaco, V. Scottez and M. Viel, 6 July 2026, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202658883
Reference: “Euclid: A UV-faint quasar in a highly luminous star-forming host galaxy at z ≈ 7.7” by S. Belladitta, R. Decarli, E. Bañados, F. Walter, D. Yang, F. Guarneri, K. Jahnke, S. Bisogni, S. E. I. Bosman, X. Fan, Y. Fu, J. F. Hennawi, Y. Matsuoka, D. J. Mortlock, M. Onoue, J.-T. Schindler, L. Spinoglio, D. Stern, F. Wang, G. Vietri, C. J. Willott, J. Wolf, J. Yang, R. A. A. Bowler, K. I. Caputi, D. L. Clements, C. M. Gutierrez, H. J. A. Rottgering, D. Scott, F. Shankar, G. Zamorani, A.-C. Eilers, B. Altieri, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, A. Balestra, S. Bardelli, P. Battaglia, A. Biviano, M. Brescia, S. Camera, V. Capobianco, C. Carbone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, A. Costille, F. Courbin, H. M. Courtois, J.-G. Cuby, A. Da Silva, H. Degaudenzi, G. De Lucia, H. Dole, M. Douspis, F. Dubath, X. Dupac, S. Dusini, S. Escoffier, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, P. Fosalba, S. Fotopoulou, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. V. H. Haugan, H. Hoekstra, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, R. Laureijs, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, S. Marcin, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Melchior, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, C. Neissner, R. C. Nichol, S.-M. Niemi, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, F. Raison, A. Renzi, J. Rhodes, G. Riccio, H.-W. Rix, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, D. Sapone, B. Sartoris, M. Schirmer, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, L. Stanco, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, L. Valenziano, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, F. M. Zerbi, E. Zucca, J. García-Bellido, J. Martín-Fleitas, P. Monaco, V. Scottez and M. Viel, 9 July 2026, Astronomy & Astrophysics.
DOI: 10.1051/0004-6361/202659319
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