Hawaiʻi telescopes help find two most distant quasars, reaching back to the universe’s first 670 million years

Four Hawaiʻi telescopes have helped confirm the two most distant quasars ever found, part of a growing partnership between the state’s premier observatories and a European Space Agency mission mapping the early universe.

The W. M. Keck Observatory and Canada-France-Hawaiʻi Telescope on Maunakea, Subaru Telescope on Maunakea, and the University of Hawaiʻi Institute for Astronomy’s Pan-STARRS Telescopes on Haleakalā are all working with the agency’s Euclid space telescope, which launched a mission in 2023 to map the large-scale structure of the universe in three dimensions and study dark energy.

The collaboration’s latest result: confirmation of 31 candidate ancient quasars, including the two most distant on record, dating to roughly the first 670 million years of the universe’s history—about 5% of its current age.

Euclid first flagged the objects because they were “dark”—undetected—in the single optical color the spacecraft captures, while showing up in its three near-infrared colors, a pattern typical of very distant objects. That signature alone isn’t enough to confirm a detection: low-mass stars called brown dwarfs can mimic the same color pattern, so researchers run extensive tests to rule out contamination before a candidate is considered credible. Subaru Telescope then contributed additional imaging, and Keck Observatory took the final step, capturing spectra of the objects to confirm what they were and how far away—and how far back in time—they actually are.

“The method is not exact,” said John O’Meara, chief scientist and deputy director at Keck Observatory, explaining why a Euclid detection alone isn’t enough. “Multiple things can sometimes have the same ratio of colors and a more exact method is needed to prove definitively what the object is. That method is to obtain a spectrum of the object, which is what the observatories here (in my case, Keck) have done.”

Jean-Gabriel Cuby, CFHT’s executive director, described what that confirmation moment is like after years of preparation: once a spectrum reveals a telltale signature called the Lyman-alpha line, “then you know you’ve made it! And for those who worked years preparing for these moments, these are extremely satisfying and rewarding moments!”

Quasars are extremely bright objects powered by supermassive black holes actively feeding at the centers of galaxies, and finding them from the universe’s infancy helps astronomers understand how galaxies and black holes formed and evolved in that early era, sometimes called “cosmic dawn.” O’Meara said the discovery effectively settles a long-running scientific debate over whether quasars could have existed that early at all.

“Finding so many can basically end the debate of whether they exist this early in cosmic time,” O’Meara said. “More data is needed, however, to determine what kind of population is out there.” He compared it to searching an airport for people over 90—finding one proves it’s possible, but understanding the group requires a much larger sample to test theories thoroughly.

Scientists have known for more than a decade that supermassive black holes—some with masses in the billions of suns—existed when the universe was under a billion years old, Cuby said. What was missing were instruments capable of pushing the search even further back; Euclid was built in part to fill that gap. NASA’s recently launched Roman Space Telescope is expected to contribute to the same effort.

Keck’s role reflects its particular strengths within the four-telescope Hawaiʻi partnership. “We combine one of the largest apertures on the ground (to see very faint objects) with precision spectrographs to determine the nature of objects and their distance,” O’Meara said, noting Keck’s mirror is the largest among the telescopes following up Euclid candidates, allowing it to study the faintest, most distant objects in the survey.

A statewide effort, years in the making

Keck’s spectroscopy is only part of the picture. The imaging that lets astronomers pick out likely distant quasars in the first place comes from a separate, Hawaiʻi-based effort: the Ultraviolet Near Infrared Optical Northern Survey, a partnership among Canada-France-Hawaiʻi Telescope, Subaru and Pan-STARRS that began surveying the northern sky in 2017—years before Euclid launched.

The partnership took years to assemble. Euclid was formally adopted as an ESA mission in 2012, and it was clear from the start that the spacecraft would need ground-based follow-up—but formalizing those partnerships took time. France, as the mission’s lead country, contributed observing time at CFHT, but not enough on its own. So Euclid’s science consortium struck a deal directly with Canadian astronomers: observing time at CFHT in exchange for roughly 30 Canadian scientists joining the Euclid collaboration.

“This was an extremely good deal for Canada because they got access to Euclid while not funding the space mission itself,” Cuby said in an email to Maui Now. A similar arrangement followed with Japan for Subaru’s time. Because Euclid is designed to survey roughly a third of the sky—including regions not visible from Hawaiʻi—the consortium also arranged for Southern Hemisphere coverage through public data from the Dark Energy Survey and, more recently, the newly operational Rubin Observatory in Chile.

Each UNIONS telescope specializes in a different slice of the color spectrum: CFHT’s MegaCam covers blue and ultraviolet light, and the observatory’s WIRCam instrument extends its reach into the near-infrared, though all of CFHT’s UNIONS contributions came from MegaCam; Pan-STARRS contributes red-light data from its long-running asteroid-tracking work; and Subaru’s wide-field Hyper Suprime-Cam adds far-red imaging. Combined, those colors let astronomers estimate how far away an object is—a measurement Euclid’s own instruments can’t produce with the same precision on their own.

“We need as many colors as possible. This is absolutely essential for the scientific objectives of Euclid, and it cannot do it alone,” Cuby said in a Sept. 9 Maunakea Observatories blog post detailing the collaboration.

Getting Euclid into space at all was not a given. The spacecraft was originally slated to launch on a Russian Soyuz rocket, but when Russia invaded Ukraine in 2022, that plan collapsed within days—with the mission nearly ready to fly. “It became a point of considerable uncertainty (and stress), since the mission was almost ready to be launched,” Cuby told Maui Now. For a few months, a delay of years was on the table before the European Space Agency arranged an alternative launch with SpaceX. Euclid finally lifted off on July 1, 2023. “You can imagine the relief for all when the mission was launched,” he said.

Yoshiki Matsuoka, an associate professor at Japan’s Ehime University who works with Subaru’s contribution to the project, said the optical imaging is what allows scientists to separate genuine distant-quasar candidates from Euclid’s broader haul of near-infrared detections. Without it, he said, identifying the faintest, most distant objects “would be like trying to recognize the color red in an RGB image without the blue channel.”

Hawaiʻi’s continuing role

Euclid has so far surveyed only a small fraction of its planned sky coverage and is expected to keep operating through the rest of the decade, meaning Hawaiʻi’s telescopes are likely to remain central to the mission’s follow-up work. O’Meara said that role will only grow as more of the sky is mapped, with Hawaiʻi facilities positioned to both flag rare, unusual objects and follow up on hundreds or thousands of quasar and gravitational-lensing candidates.

He also pointed to the discovery as evidence of Maunakea’s continued relevance in an era when ground-based astronomy increasingly depends on partnerships with space missions. “Maunakea’s facilities combined are unmatched in the ability to provide the ground-based survey response,” O’Meara said, adding that reaching the faintest objects and gathering quality spectra requires “a dark, dry, stable sky” and broad sky visibility that Maunakea offers better than any other site in the world.

Cuby went further, tying the discovery directly to the debate over Maunakea’s future.

Astronomy’s case for staying on the mountain “is not a self-sufficient argument,” he said—the field also has to change how it operates there.

“It is absolutely essential for astronomy to change its approach to its practice, and to engage in a meaningful and reciprocal manner with Hawaiʻi’s local communities, and with the MKSOA process,” Cuby said, referring to the state’s Maunakea Stewardship and Oversight Authority. He said CFHT is “committed to actively and genuinely participating in this process,” and pointed to “the inalienable right of the local population to determine the use of these lands in a manner that serves them best.”

“Astronomy is a global science,” he said. “Observatories are complementary to each other, more than competing between themselves. Hawaiʻi is unique for Northern sky observations. Some capabilities available in Hawaiʻi are not available anywhere else. Without Hawaiʻi, the scientific outcome of the Euclid mission (or of any other mission, for that matter), would be reduced.”