ESA's Euclid Telescope Finds 31 Ancient Quasars, Two Records From 670 Million Years After the Big Bang

Two of the objects in ESA's latest Euclid catalogue are the most distant quasars ever recorded. Each was already blazing roughly 670 million years after the Big Bang, with the brightness of a trillion Suns. They are part of a haul of 31 ancient quasars identified in data from the Euclid space telescope, which launched in 2023.

A quasar is what a galaxy's core looks like during a brief, violent phase. Huge quantities of gas and other material spiral toward the supermassive black hole at the center and release enormous amounts of energy. The core then outshines the rest of the galaxy, by hundreds or even thousands of times. Astronomers have hunted for the earliest ones for decades, because they carry clues about how the first galaxies and supermassive black holes formed. The hunt is hard. Few galaxies had grown large enough at that stage to host such an object, the light that reaches us is extremely faint, and the sources are easily confused with much closer stars.

The two record holders are EUCL J172902.75+641018.1, with a redshift of 7.77, and EUCL J125308.55+705432.3, at 7.69. Redshift measures how far light has been stretched by the expanding Universe, and so how far back in time it set out. Both objects lie just over 13 billion light-years away. The previous record, set by an object found in 2021, was a redshift of 7.64. Antonio La Marca, an ESA Research Fellow on the Euclid team, says the finding more than doubles the number of quasars known from so early an era.

Twelve of the 31 quasars have a redshift of 7 or greater, which places them within the Universe's first 770 million years. The pace is striking. Astronomers needed more than a decade to find roughly the first 10 quasars at that distance, and Euclid has passed that number in about a year. La Marca describes the result as the first true census of quasars at the dawn of the Universe.

The sample also differs in kind. Until now, most known early quasars were exceptionally luminous ones that were simply easier to spot, which made it hard to understand the wider population. Euclid is also finding much fainter examples that earlier searches missed. Daming Yang of Leiden University, lead author of the discovery paper, calls the telescope a true game-changer. Where researchers once found only a handful of the very brightest, he says, they can now search far more efficiently across huge areas of sky.

Follow-up work has already begun on one of the new finds. Silvia Belladitta and colleagues studied the second most ancient quasar in more detail. They found it sits inside a galaxy rich in gas and dust, where new stars are forming at a tremendous rate. That offers a glimpse of the surroundings of an early supermassive black hole, and may help explain how the first massive galaxies grew alongside the black holes at their centers.

These quasars also belong to the epoch of reionization. In that era the Universe emerged from its cold, dark state, the so-called dark ages, as energetic radiation heated the surrounding gas and ionized it. ESA Euclid Project Scientist Valeria Pettorino calls ancient quasars rare discoveries and time machines that let astronomers explore how the first generation of galaxies came to be. She credits the combination of wide sky coverage, depth, sharp imaging and space-based infrared vision, along with thousands of Euclid Consortium scientists and engineers who sift the data. Candidates are then studied further with ground-based telescopes.

All 31 came from the Euclid Wide Survey, which will eventually cover more than one-third of the sky. Euclid's main mission is to investigate the dark Universe, but the survey is also turning up these rare objects as a byproduct. Astronomers expect the growing collection to help answer a long-standing question: how supermassive black holes became so enormous so soon after the Big Bang.