University of Michigan researchers were part of an international team that used the European Space Agency’s Euclid space telescope to discover 31 of the most ancient quasars ever observed.
They are so old, in fact, that they date back to the universe’s so-called reionization era, when stars, galaxies and supermassive black holes were first forming.
“This is truly exciting,” said Jinyi Yang, co-author of the new study published in the journal Astronomy & Astrophysics and assistant professor in the U-M Department of Astronomy. “These luminous quasars, shining from deep within the reionization era, the last major transition in our universe’s history, offer invaluable insights into how the cosmos emerged from darkness and how the earliest supermassive black holes formed.”
Quasars are among the brightest, most energetic objects in the universe and are powered by supermassive black holes devouring matter at the center of galaxies. They are short-lived compared to a galaxy’s lifetime, but in that relatively brief moment, quasars can outshine the rest of their host galaxies by hundreds to thousands of times.
By finding the most distant quasars, astronomers can learn more about the early universe. But ancient quasars are rare because few galaxies had enough time to grow large enough to host one. These quasars are also hard to find because their primordial light is both faint and easy to confuse with stars.
But Euclid, which began its cosmological survey in February 2024, is ushering in a new era in that search, said study co-author Feige Wang, U-M assistant research scientist in astronomy.
“The Euclid mission is completely changing the game,” Wang said. “Of those 31 quasars, 12 are above redshift 7, more than doubling all the known quasars that are beyond redshift 7.”
Redshift is a measure of how much the wavelength of light from an astronomical object has been stretched due to the expansion of the universe. Light that travels longer to reach us—that is, light from distant sources that was emitted long ago—will have higher redshifts. In this sense, observing objects with high redshifts allows astronomers to look back in time and study the universe when it was younger, Wang said.
Previously, the record for the most distant quasar was held by one discovered in 2021 by Wang and Yang with a redshift of 7.64. The new study includes two quasars that break that record: one with a redshift of 7.69 and another with a redshift of 7.77. That means both emerged within 670 million years of the Big Bang and their light took more than 13 billion years to reach us.
To 8 and beyond
What sets Euclid apart is its unprecedented combination of depth and sky coverage. This allows the space telescope to detect quasars 10 to 100 times fainter than those found in earlier wide-field surveys.
“It’s a unique tool for quasar hunting,” said Daming Yang, lead author of the new study and a doctoral student at Leiden University in the Netherlands. “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.”
Although Euclid is now accelerating the discovery of ancient quasar candidates, astronomers also rely on a battery of other telescopes and instruments to confirm and characterize these objects. For instance, Jinyi Yang, Wang and their teams, including U-M postdoctoral researcher Xiangyu Jin, led efforts with the Magellan Telescopes at Las Campanas Observatory in Chile to analyze the Euclid quasar candidates. They confirmed 10 of the 31 quasars found in this study.
Moving forward, they and their colleagues on the Euclid Consortium—made up of 2,600 members from 18 countries—will keep searching for more and older quasars to answer questions about the early universe.
For their part, Yang and her team are investigating how these early supermassive black holes grow and impact the evolution of their host galaxies. Wang’s team is exploring the large-scale environments around these quasars, examining their place in the cosmic web of galaxies and what they can tell us about how it was spun.
The newly discovered quasars could also help in both projects by providing targets for the Extremely Large Telescope when it comes online, which is anticipated to be 2029. The 39-meter telescope will be the world’s largest working with visible and infrared light wavelengths and U-M is the only U.S. university participating in its design and construction. That means its students, staff and faculty will have unique opportunities to pursue their research goals with this state-of-the-art observatory.
“We want to answer questions about how these quasars formed, what were the black holes like that seeded them and how did they grow up,” Yang said. “The current observations of distant quasars are challenging existing models of black hole seeds and early growth. Every time we get new observational evidence from new quasars, we can put tighter and tighter constraints on these models.”
And Euclid will soon have more help in this new age of quasar discovery. The Vera Rubin Observatory started its survey of the heavens last year from a mountaintop in Chile using the world’s largest camera. And the Roman Space Telescope is slated to launch Aug. 30 with a field of view that will be 100 times larger than the Hubble Space Telescope.
“We will basically have three really powerful survey telescopes within the next year and they will allow us to push the redshift frontier,” Wang said. “Pushing to redshift 9 may take a few years, but I think we may see a redshift of 8 very soon.”
