The moment when an enormous burst of light exploded from a black hole that had been sucking in all matter just after the universe was born has been captured. Because it happened so long ago, the light itself has faded, and in the meantime many bright stars have formed around us, making it harder than finding a needle in a haystack. Scientists say they can shed more light on the upheavals of the early universe by seeing it in its infancy.
The European Space Agency (ESA) said on the 6th that "in March, the Euclid space telescope discovered 31 quasars, more than doubling the number observed so far." A quasar is a phenomenon in which matter around a black hole shines as the brightest light in the universe. It is more than 1 trillion times brighter than the sun. Two of them occurred when the universe was only 5% of its current age, making them the oldest quasars ever observed. A paper with the findings was published the same day in the international journal "Astronomy & Astrophysics."
◇Light exploded from the abyssal black hole of the universe
A black hole is the state of a star that has reached the end of its life, exploded, and collapsed to an extreme. If a mass about the size of Earth became a black hole, it would shrink to a diameter of 1 cm. In that case, gravity—the force that pulls objects—becomes so strong that, true to its English name meaning "black hole," not even light can escape. Although black holes are invisible abysses of the universe, quasars reveal their presence. As matter is drawn into a black hole and orbits around it at tremendous speeds, friction among the material emits powerful light.
Of the quasars discovered this time, 12 formed when the universe was less than 6% of its current age. The Euclid international consortium team determined the quasars' ages using the so-called redshift phenomenon. Redshift is the stretching of light's wavelength toward the red as the universe expands. Redshift is easier to understand by comparing it to changes in a siren's sound.
When an ambulance approaches, its siren sounds higher, but as it passes and moves away, the sound becomes lower. Higher sounds have shorter wavelengths, and lower sounds have longer wavelengths. Likewise, celestial bodies in the early universe recede with the expansion of the universe, shifting their light toward the longer, red wavelengths.
The 12 quasars showed redshifts of 7 or more. That means the wavelengths of light from extremely distant objects have stretched sevenfold as the universe expanded. Joseph Hennawi, a co-author of the paper at Leiden University in the Netherlands, said, "A redshift of 7 takes us back to just 750 million years after the universe was born," adding, "That is a time less than 6% of the universe's current age."
Among them, EUCL J172902.75+641018.1 and EUCL J125308.55+705432.3 were confirmed with redshifts of 7.77 and 7.69, respectively. They appeared within the first 670 million years after the birth of the universe, setting the record as the oldest quasars discovered to date. Both objects are just over 13 billion light-years away (a light-year is the distance light travels in one year, about 9.46 trillion km). In other words, we are observing galaxies from about 13 billion years ago.
◇Hopes it will help understand early-universe upheavals
Quasars in the early universe are expected to greatly help reveal how the supermassive black holes that power them formed so early. Hennawi said, "These monstrous objects, with masses of billions of times that of the sun, existed when the universe was newborn, but we have not understood how they acquired such enormous mass so quickly."
Scientists spent decades searching for the universe's first quasars to uncover how supermassive black holes formed, but results were modest. In the early universe, galaxies had too little time to grow large, so quasars themselves were rare. Even when they did form, their light dimmed over vast time, making them hard to distinguish from other bright nearby stars today.
Euclid has completely changed the level of quasar research. The international consortium team said the discovery more than doubled the number of quasars formed in the early universe. It took more than 10 years to find just over 10 quasars with redshifts of 7 or higher, but Euclid found more than that in just one year.
Euclid is a space telescope launched in July 2023 that is surveying the entire sky with high-sensitivity cameras to compile a catalog of billions of galaxies. Currently, more than 2,000 scientists from 15 European countries, the United States, Canada, and Japan are conducting research in the Euclid consortium.
According to the consortium, Euclid's unrivaled infrared observation capability can find rare and extremely distant objects far more efficiently than before. In particular, Hennawi explained, "Thanks to recent artificial intelligence search algorithms, we can review data on tens of millions of targets and conclusively select only the small number of true quasars."
References
Astronomy & Astrophysics (2026), DOI: https://doi.org/10.1051/0004-6361/202658883