Euclid was built mainly to map the large-scale universe. Barely into its survey, it has already changed the census of some of the earliest known quasars.

In a paper accepted for publication in Astronomy & Astrophysics and posted to arXiv on 3 July 2026, D. Yang and more than 200 colleagues report 31 newly identified quasars at redshifts between 6.6 and 7.8. In ordinary time language, their light comes from when the universe was still within its first billion years. The most distant of the group, EUCL J172902.75+641018.1 at about redshift 7.77, is described by the team as the most distant quasar yet reported.

This is one accepted paper, not settled consensus. The objects still need the usual follow-up work that early-universe astronomy demands, especially for black hole masses and host-galaxy properties. But the discovery matters because quasars are not just bright dots. They are powered by gas falling into massive black holes, and finding more of them this early adds pressure to a problem astronomers have been wrestling with for years: how did some black holes become so large so fast?

What Euclid found

The 31 quasars were selected from roughly 3,000 square degrees of sky covered during the first 1.5 years of the Euclid Wide Survey. The search used Euclid’s visible and near-infrared images, plus additional ground-based data where available, to pick out candidates whose colours looked like very distant quasars rather than nearby cool stars or compact galaxies.

That photometric sorting was only the first step. The team then used spectroscopic follow-up with Keck, Magellan and the Large Binocular Telescope to confirm the objects. Spectroscopy is crucial here because redshift is not a decoration on the result. It is the distance and time measurement. A quasar at redshift 7.7 is being seen as it was roughly 670 million years after the Big Bang.

The new sample includes 12 quasars at redshift 7 or higher, more than doubling the previously known number in that range, according to the paper. It also pushes into fainter territory than many earlier high-redshift quasar searches, with rest-frame ultraviolet magnitudes from about -25.5 to -23.6. That matters because the earliest known quasars used to be found mostly by hunting the brightest examples. Euclid is beginning to fill in the less extreme population.

Why quasars are a black hole problem

A quasar is not a galaxy shining normally. It is an active galactic nucleus: a central black hole surrounded by infalling gas that becomes hot enough to radiate across enormous distances. The black hole itself is dark, but the accretion process can outshine the stars around it.

That is why ancient quasars are so awkward. If a quasar is already visible less than a billion years after the Big Bang, then its central black hole has already formed, found fuel and grown large enough to power a beacon that can be seen across most of cosmic history. In the simplest picture, a black hole seed forms from the death of an early massive star, then grows by accreting gas. But growth is limited. Radiation from the accretion flow pushes back against infalling material, creating what astronomers call the Eddington limit.

There are ways around the timing problem, but none is trivial. The seed black holes could have been unusually massive from the start, perhaps formed by the direct collapse of gas clouds. They could have grown during episodes of super-Eddington accretion, where gas falls in faster than the textbook limit under special conditions. They could have merged with other black holes. Or some combination of these processes may have operated in the dense early universe.

The point is not that the Euclid objects make black hole growth impossible. They make the accounting harder and much more interesting. Each additional quasar at redshift 7 or beyond is another marker showing that massive accreting black holes were not rare curiosities by that time.

The record object is only part of the story

The most attention-grabbing source in the sample is EUCL J172902.75+641018.1, at redshift about 7.77. Another very early source, EUCL J125308.55+705432.3, sits at a similar epoch and has already been studied in a companion paper led by S. Belladitta. That follow-up used NOEMA observations to detect [CII] emission and cold dust in the quasar host galaxy, setting a systemic redshift of 7.6980 plus or minus 0.0004.

That second paper is useful because it shows why the next stage is not simply counting quasars. EUCL J125308.55+705432.3 is relatively faint in rest-frame ultraviolet light compared with previously known quasars around redshift 7.5, yet its host shows bright [CII] emission and signs of intense star formation. The authors estimate a star-formation rate above 250 solar masses per year. In other words, some of these early quasars may sit in dusty, actively growing galaxies that older optical searches were less likely to find.

That changes the sample bias. If early quasar searches mainly found the brightest objects not hidden by dust, then the known population was never a neutral inventory of early black holes. Euclid’s wide-area infrared survey can find objects that are fainter in the ultraviolet or otherwise easier to miss. The 31 new quasars may therefore be less a final answer than an opening of the search space.

A result that was anticipated, but still matters

Euclid finding early quasars is not a total surprise. A 2019 Euclid preparation paper predicted that the wide survey should be able to identify large numbers of quasars beyond redshift 7, including objects fainter than many previous searches could efficiently select. But predictions and confirmed spectra are different things. The new paper reports confirmed quasars, not just candidates selected by colour.

The scale also matters. Before Euclid, quasars at redshift 7 and above were found one by one, after difficult searches through vast catalogues contaminated by nearby objects that can mimic their colours. Adding 12 such quasars in one early release more than doubles the known sample, giving astronomers a better way to test how common these objects are and how quickly their number density falls with redshift.

The discovery also reaches into the epoch of reionisation, the period when the first stars, galaxies and accreting black holes transformed the intergalactic gas from mostly neutral to ionised. Quasars are useful probes of that process because their spectra carry absorption signatures from material between the quasar and Earth. More high-redshift quasars mean more sightlines through the early intergalactic medium.

What this does not prove

The careful version is important. The paper does not by itself solve the origin of the first supermassive black holes. It also does not mean every one of the 31 objects has a precisely measured black hole mass. Quasar luminosity tells astronomers that an accreting black hole is present, but turning spectra into black hole masses requires further observations and modelling.

Still, the timing is severe. Earlier discoveries already showed billion-solar-mass black holes around redshift 7, including the redshift 7.642 quasar reported by Feige Wang and colleagues in 2021. Reviews of massive-black-hole origins, including work by Marta Volonteri, Melanie Habouzit and Monica Colpi, describe several possible seed and growth channels precisely because ordinary stellar-remnant growth struggles to explain the most extreme early quasars without special conditions.

Euclid’s 31 quasars do not replace that theoretical problem. They widen it. Instead of asking only how one or two extraordinary black holes formed early, astronomers can now ask how common such engines were, how varied their host galaxies were, and whether the early universe produced massive black holes through one dominant route or several.

The answer will probably come from combining Euclid’s wide survey with deeper follow-up from telescopes such as JWST, ALMA, NOEMA and the largest ground-based observatories. Euclid can find the needles across a very large field. Other instruments can then study the metal content, dust, gas, star formation and black hole masses in detail.

For now, the discovery is a census shock rather than a complete explanation. There were more bright black-hole engines operating near the dawn of cosmic history than the old sample made visible. The next problem is working out how the universe built them in time.

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