An international team of scientists has discovered 31 of the most ancient quasars ever found. Quasars are among the brightest, most energetic objects in the universe, powered by supermassive black holes devouring matter at the centers of galaxies. Their extreme luminosity makes them visible across tremendous cosmic distances.

Two of these discoveries represent the earliest quasars yet observed in cosmic history. They radiated the light of a trillion suns when the universe was merely 670 million years old. The findings, published in the journal Astronomy & Astrophysics, represent significant progress in understanding the early universe.

“These objects provide the best clues for understanding how supermassive black holes form. These monsters — weighing billions of times the mass of our sun — somehow already existed when the universe was in its infancy.”

Joseph Hennawi, physics professor with joint appointments at UC Santa Barbara and Leiden University

Astronomers have pursued the universe’s first quasars for decades. These objects reveal what occurred during the cosmos’ earliest period, including how the first supermassive black holes and galaxies formed. However, quasars from earlier than approximately 770 million years after the Big Bang remain exceedingly rare and difficult to detect. Few galaxies had grown large enough to generate a quasar, and their light is stretched from ultraviolet into near-infrared wavelengths by cosmic expansion, falling into a range where Earth’s atmosphere glows brightly, drowning out faint signals.

“A redshift of 7 takes us to when the universe was just 750 million years old, less than 6% of its current age.”

Joseph Hennawi

Lead author Daming Yang, a doctoral student in Hennawi’s group at Leiden University, noted the challenge: “For every one of them there are thousands of stars in our Milky Way and nearby galaxies that look almost identical in the imaging surveys. And since their light is stretched to the infrared at such distances, we need a survey that is both wide enough to capture these rare objects and deep enough to detect their faint light.”

In 2023, the European Space Agency launched the Euclid space telescope to investigate this era. It views the universe from above Earth’s infrared haze, surveying an area of sky far larger than ground-based observatories could cover at comparable depth. The telescope has discovered an unprecedented 31 new quasars in the early universe, pushing back to a time when the cosmos was just 5% of its current age.

“Euclid is a true game-changer. 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 to capture much fainter light.”

Daming Yang

The second most ancient quasar was recently studied in greater detail. Analyses revealed it was embedded in a dusty, gas-filled galaxy that was actively forming new stars, providing insight into what the host galaxy of an early supermassive black hole may have resembled.

These quasars date to the epoch of reionization — when the first stars and galaxies ionized the dark, neutral hydrogen fog filling the early universe. This crucial era set the stage for everything observed today.

Of the 31 new quasars, 14 are at or above a redshift of 7. The two most ancient have redshifts of 7.69 and 7.77, setting a new record for earliest quasars ever found. Both lie just over 13 billion light-years away, emerging during the universe’s first 670 million years. They break 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? We’re finding black holes with hundreds of millions of times the mass of our sun at a time when the universe was barely getting started.”

Joseph Hennawi

Better telescopes and smarter searches have enabled astronomers to continue examining deeper into the universe’s history. Discovering the first 10 or so quasars at a redshift of 7 or above took more than a decade — but Euclid discovered more than that in a single year. This discovery more than doubles the number of known ancient quasars.

Beyond revolutionary observatories like Euclid, new machine-learning methods enable scientists to filter through tens of millions of sources and reliably identify genuine quasars from far more common imposters. Hennawi’s group has spent years developing algorithms critical to these recent discoveries. He also leads PypeIt development, software that astronomers at the University of California use to process data collected at the Keck telescopes. Two-thirds of these new quasars, including the three most distant, were discovered through UC’s privileged Keck access.

The team’s current objective is to push the distance frontier even further, finding the first quasar beyond redshift 8, which would place it within the first 630 million years of the universe’s existence.

Discovery represents only part of the investigation. The team has approved programs with the James Webb Space Telescope to study many of these quasars in detail, including measuring their black hole masses, probing the chemistry of surrounding gas, and using the imprint of the intergalactic medium on their light to trace reionization’s progression. Meanwhile, telescopes like the Atacama Large Millimeter Array will examine the cosmic dust glowing in the host galaxies themselves, revealing details about their dust, gas, and star formation.

“The bigger vision is to stitch all of this together into a coherent timeline: a quasar chronicle of the first billion years.”

Joseph Hennawi

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Journal: Astronomy & Astrophysics
DOI: 10.1051/0004-6361/202658883