Astronomers have spotted the oldest quasars ever seen – brilliant beacons powered by supermassive black holes that were already blazing when the universe was just 670 million years old. Using Europe's Euclid space telescope, an international team identified 31 of these ancient objects, including the two earliest known examples. The findings were published in the journal Astronomy & Astrophysics.
Quasars rank among the brightest objects in the cosmos: supermassive black holes at the centres of galaxies devour surrounding matter and shine with the light of roughly a trillion suns, visible across billions of light years. The two record-holders in the new haul, seen just over 13 billion light years away, have redshifts of 7.69 and 7.77 – making them the earliest quasars ever identified and surpassing a record the same group set in 2021.
Such objects are extraordinarily hard to find. Very few galaxies in the young universe had grown large enough to host them, and their faint light – stretched by cosmic expansion from ultraviolet into the infrared – is easily lost among thousands of nearby stars that look almost identical. Earth's atmosphere glows at exactly those wavelengths, which is why the search all but requires a telescope in space.
A game-changer above the atmosphere
That telescope is Euclid, launched by the European Space Agency in 2023. Operating above the atmospheric glow, it surveys vast swaths of sky at remarkable depth; once complete, its Wide Survey will map more than a third of the entire sky. "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," said lead author Daming Yang, a doctoral student at Leiden University. It took astronomers more than a decade to find the first ten quasars from this distant era; Euclid turned up more than that in a single year, more than doubling the known population.
The quasars date to the epoch of reionisation, when the first stars and galaxies flooded space with light and transformed the young cosmos. Studying them may help crack a deepening puzzle. One of the oldest quasars in the new batch sits inside a dusty, gas-rich galaxy convulsed by an intense burst of star formation – a possible clue to how the first giant black holes fed and grew.
"These monsters – weighing billions of times the mass of our sun – somehow already existed when the universe was in its infancy," said co-author Joseph Hennawi, who holds appointments at UC Santa Barbara and Leiden University. "We don't yet have a good understanding of how they grew so massive, so fast." Each step further back in time, he added, sharpens the question – and, with Euclid and machine-learning search tools, astronomers now have far more examples to study.