Quasars rank among the brightest and most powerful objects in the universe, powered by supermassive black holes at galactic cores that emit energy detectable across billions of light‑years.
An international team of researchers has identified 31 of the earliest quasars ever found, including the two oldest known examples. These objects emitted the equivalent of about a trillion suns when the universe was merely 670 million years old. Published in Astronomy & Astrophysics, the findings provide an unprecedented view of the universe’s earliest epochs.
“These objects give us the clearest clues about how supermassive black holes form,” said co‑author Joseph Hennawi, a physics professor with joint appointments at UC Santa Barbara and Leiden University. “These behemoths — hundreds of billions of times the Sun’s mass — already existed when the universe was still in its infancy, and we lack a full explanation of how they grew so quickly.”
Challenges in Detecting Ancient Quasars
For decades, astronomers have searched for the universe’s earliest quasars because they hold valuable insight into how the first galaxies and supermassive black holes formed.
Nevertheless, detecting them is extremely difficult. Quasars that formed less than about 770 million years after the Big Bang are exceedingly rare, as only a few galaxies had grown sufficiently massive to host them. Their faint light is also easily mistaken for that of nearby stars in our own galaxy.
Another challenge stems from the universe’s expansion: the light from these distant quasars shifts from ultraviolet into the near‑infrared. Earth’s atmosphere emits strongly in these wavelengths, which hampers ground‑based telescopes from detecting such faint sources.
Astronomers use this effect, called redshift, to gauge both distance and age; a higher redshift indicates a more distant, earlier object. “A redshift of 7 corresponds to a time when the universe was only 750 million years old — less than 6% of its present age,” Hennawi explained.
“These factors make finding quasars at such distances incredibly challenging,” said lead author Daming Yang, a doctoral student in Hennawi’s group at Leiden University. “For each quasar there are thousands of Milky Way stars and nearby galaxies that appear nearly identical in imaging surveys, and because their light is shifted into the infrared at such distances, we require a survey that is both wide enough to capture these rare objects and deep enough to detect their faint emission.”
Given these constraints, ground‑based searches are nearly impossible; space‑based observations provide a far clearer view.
Euclid Space Telescope Discovers 31 Ancient Quasars
The European Space Agency launched the Euclid space telescope in 2023 to study the universe during this pivotal era. Positioned above Earth’s atmosphere, Euclid avoids the infrared glow that limits ground‑based observations while mapping vast regions of the sky with remarkable depth.
Using data from the Euclid Wide Survey, researchers identified an unprecedented 31 new quasars from the early universe. When the survey is complete, it will map more than one‑third of the entire sky. Some of these newly discovered quasars originate from a period when the universe was only about 5% of its current age.
Until now, astronomers had primarily detected only the brightest and rarest ancient quasars, limiting the sample size for studying the early quasar population as a whole.
“Euclid is a true game‑changer,” Daming said. “Previously we could only locate a handful of the brightest ancient quasars, but Euclid enables us to search far more efficiently across vast sky areas to detect much fainter objects. It is a unique instrument for quasar hunting.”
Insights Into the Universe’s First Billion Years
Researchers recently examined the second oldest quasar in detail and found that it resides in a dusty, gas‑rich galaxy experiencing an intense burst of star formation, offering new clues about the environments where the earliest supermassive black holes grew.
These newly discovered quasars originate from the epoch of reionization, when the first stars and galaxies ionized the neutral hydrogen that once filled space, shaping the evolution of the cosmos that followed.
Of the 31 newly discovered quasars, 14 have redshifts of 7 or higher. The two oldest, with redshifts of 7.69 and 7.77, represent the earliest quasars ever identified. Located just over 13 billion light‑years away, they are observed as they existed within the universe’s first 670 million years and surpass the previous record set by Hennawi’s group in 2021.
“Every step further back in time makes the puzzle more perplexing: How did the Universe produce supermassive black holes so quickly?” Hennawi said. “We are finding black holes with hundreds of millions of solar masses at a time when the universe was just beginning.”
Exploring Deeper Into Cosmic History
Astronomers have steadily pushed farther back into cosmic history using improved telescopes and sophisticated search techniques. It took more than a decade to discover roughly the first 10 quasars with redshifts of 7 or higher. Euclid has already identified more than that in a single year, effectively more than doubling the known population of these extremely ancient objects.
Machine learning has also become essential to the search. According to Hennawi, advanced algorithms can now examine tens of millions of astronomical sources and separate the few genuine quasars from the vast number of look‑alike stars and galaxies.
Hennawi’s team spent years developing many of the algorithms used in these discoveries. He also leads development of PypeIt, the software used by astronomers at the University of California to process observations from the Keck telescopes. Through UC’s observing access, Keck confirmed two‑thirds of the newly discovered quasars, including the three most distant examples.
The researchers are now aiming to discover the first quasar with a redshift greater than 8, which would reveal an object existing within the universe’s first 630 million years.
James Webb and ALMA Will Study These Ancient Giants
Finding these quasars is only the beginning. The team has secured observing time with the James Webb Space Telescope to study many of them in detail. Future observations will measure the masses of their black holes, analyze the chemistry of the surrounding gas, and use their light to trace how reionization unfolded across the early universe.
Meanwhile, the Atacama Large Millimeter Array will study the dust, gas, and star formation within the galaxies hosting these ancient quasars, offering an even clearer picture of how the earliest massive galaxies evolved.
“The bigger vision is to stitch all of this together into a coherent timeline,” Hennawi said, “a quasar chronicle of the first billion years.”
Daming Yang, Antoine Basset, and Jean-Charles Cuillandre of the Euclid Consortium contributed to this story.
