Euclid Telescope Discovers 31 Ancient Quasars, Challenging Models of Early Supermassive Black Hole Formation

The European Space Agency's Euclid space telescope has identified 31 of the most ancient quasars ever observed, fundamentally altering our understanding of the early universe. Among this unprecedented haul are the two most distant quasars on record, shining brightly when the cosmos was merely a fraction of its current age. The findings, published in the peer-reviewed journal Astronomy & Astrophysics, push the boundaries of cosmic observation back to the universe's infancy, capturing light that has traveled for over 13 billion years to reach Earth. This discovery represents a major milestone in observational cosmology, providing a wealth of new data that challenges existing models of how the first supermassive black holes formed and grew so rapidly in the immediate aftermath of the Big Bang.[1][2][3]

Quasars are the intensely luminous cores of active galaxies, powered by supermassive black holes actively consuming vast amounts of surrounding gas and dust. During this brief, violent phase of a galaxy's evolution, the material spiraling into the black hole forms an accretion disk that heats up to extreme temperatures, releasing enormous quantities of energy across the electromagnetic spectrum. A single quasar can outshine its entire host galaxy by a factor of hundreds or even thousands, making them some of the brightest objects in the universe. It is this extreme luminosity that allows astronomers to detect them across vast cosmic distances, using them as brilliant beacons to illuminate the dark, early epochs of cosmic history.[1][4]

The two record-breaking quasars discovered by the Euclid team, designated EUCL J172902.75+641018.1 and EUCL J125308.55+705432.3, have confirmed redshifts of 7.77 and 7.69, respectively. In cosmology, redshift is a critical measure of distance and time; as the universe expands, the light from distant objects is stretched into longer, redder wavelengths. These extreme redshift values surpass the previous record of 7.64 set in 2021, placing the existence of these two quasars at just 670 million years after the Big Bang. To put this into perspective, they were already shining with the light of a trillion suns when the universe was merely 5% of its current age of 13.8 billion years, a time period often referred to as the Cosmic Dawn.[2][4]

This discovery fundamentally challenges existing astrophysical models regarding the formation and growth of supermassive black holes in the early cosmos. To power such intensely luminous quasars, the central black holes must have already grown to enormous masses—likely millions or even billions of times the mass of our Sun. Theoretical models struggle to explain how black holes could accumulate such immense mass in the relatively short cosmic timeframe of 670 million years. In the standard model of black hole evolution, they grow gradually by accreting matter or merging with other black holes, a process that should take billions of years to produce the behemoths observed by Euclid. The evidence suggests a critical gap in our current understanding of early cosmic mechanics.[5][6]

To resolve this theoretical tension, astrophysicists propose two primary hypotheses. The first suggests that the initial "seed" black holes were much larger than previously thought, perhaps formed from the direct, rapid collapse of massive primordial gas clouds rather than the slow death of individual early stars. The second hypothesis posits that these early black holes experienced periods of "super-Eddington accretion," consuming matter at rates that far exceeded the theoretical limits known as the Eddington limit, where the outward pressure of radiation should theoretically halt further inward flow of gas. The Euclid data provides crucial new evidence to test these competing theories, offering a larger sample size to analyze the growth curves of these ancient objects.[2][6]

Prior to the launch of Euclid, finding quasars from this specific epoch, known as the Epoch of Reionization, was exceptionally difficult and yielded only a handful of the brightest outliers. Ground-based telescopes struggled with the extreme faintness of the objects and the interference of Earth's atmosphere, which absorbs much of the infrared light necessary to spot high-redshift targets. Furthermore, ancient quasars are incredibly rare, as very few galaxies in the early universe had had enough time to grow large enough to host a supermassive black hole. Their primordial light is also easily confused with the signatures of much closer, cooler stars within our own Milky Way, requiring painstaking analysis to separate the true distant quasars from local cosmic noise.[3][5]

Euclid's unique design and capabilities allowed it to overcome these historical observational hurdles. Positioned 1.5 million kilometers from Earth at the second Lagrange point (L2), the telescope combines a massive field of view with highly sensitive near-infrared instruments. This allows Euclid to survey vast swaths of the sky efficiently, capturing the faint, highly redshifted light that optical telescopes miss. In just its first year of observations, analyzing data from the Euclid Wide Survey, the telescope has more than doubled the number of known quasars with a redshift greater than 7. This is a remarkable milestone that previously took the global astronomical community over a decade to achieve using a patchwork of ground-based observatories.[1][2][4]

The process of identifying these ancient beacons involved a sophisticated, multi-layered approach. The initial candidates were flagged using advanced machine learning algorithms designed to sift through Euclid's massive datasets, looking for specific "dropout" signatures—sharp cutoffs in the light spectrum that are characteristic of high-redshift objects absorbed by intergalactic hydrogen. Once the candidates were identified by the software, they required rigorous confirmation to ensure they were indeed distant quasars and not local artifacts. This confirmation was achieved through extensive spectroscopic follow-up observations using some of the most powerful ground-based facilities on Earth, including the Keck Observatory in Hawaii, the Magellan Telescopes in Chile, and the Subaru Telescope.[2][6]

Crucially, the newly discovered quasars are notably fainter than the handful of previously known ancient quasars. While earlier discoveries represented only the absolute brightest, most extreme outliers of the early universe, the Euclid sample provides a much more representative look at the general early quasar population. This broader, fainter sample is vital evidence for astronomers attempting to accurately map the quasar luminosity function—a measure of how many quasars exist at different brightness levels. Understanding this distribution is essential for calculating the overall energy output of quasars during the universe's infancy and determining their precise role in shaping the evolution of early galaxies.[2][5]

This expanded population data feeds directly into one of the most pressing questions in modern cosmology: what drove the Epoch of Reionization? During this period, the neutral hydrogen gas that filled the early universe was ionized, stripping electrons from protons and making the cosmos transparent to light as we see it today. The exact sources of this massive flood of ionizing radiation—whether it was primarily driven by the collective light of the first generation of stars in early galaxies, or by the intense radiation emitted by early quasars—remains a subject of intense debate. The 31 new quasars discovered by Euclid provide critical new data points to help resolve this mystery.[5][6]

While the discovery of the quasars themselves is robustly supported by the spectroscopic follow-up data, significant uncertainties remain regarding their exact physical properties. The precise masses of these newly discovered supermassive black holes have yet to be directly measured, leaving theoretical astrophysicists to rely on estimates derived from their luminosity. Furthermore, the environments surrounding these quasars—the host galaxies that feed them—remain largely hidden from view, obscured by the intense glare of the central black hole. Transparently acknowledging these unknowns is a core component of the evidence pack, highlighting where the current data ends and where future observational campaigns must begin.[2]

To bridge this gap in understanding, future observations will heavily rely on the James Webb Space Telescope (JWST). While Euclid is designed as a survey telescope to find these rare objects across wide areas of the sky, JWST acts as a precision instrument capable of zooming in on individual targets with unprecedented resolution. Follow-up observations with JWST will be necessary to characterize the host galaxies of these quasars, accurately weigh their central black holes using detailed spectroscopic analysis, and map the surrounding intergalactic medium. As Euclid continues its six-year mission to map one-third of the sky, astronomers anticipate the discovery of hundreds more ancient quasars, providing the definitive evidence needed to rewrite the rules of early black hole formation.[1][2][6]