Discoveries From Maunakea Reveal Hidden Worlds Around Accelerating Stars

Astronomers using W. M. Keck Observatory and the Subaru Telescope on Maunakea, Hawaiʻi Island have discovered a massive planet and a brown dwarf orbiting distant stars—two rare companions that deepen our understanding of how giant planets and substellar objects form and evolve.

These discoveries are the first results from the OASIS program (Observing Accelerators with SCExAO Imaging Survey), a new large-scale survey that combines precision stellar motion data from space-based missions with the cutting-edge imaging capabilities of Maunakea’s observatories.

“These discoveries may help advance our abilities to image another Earth with future space-based observatories such as NASA’s Roman Space Telescope. These results show what happens when we combine Maunakea’s unmatched observing conditions with cutting-edge instrumentation,” said Thayne Currie, professor at The University of Texas at San Antonio and principal investigator of OASIS.

The pair of studies, led by The University of Texas at San Antonio, are published in the The Astronomical Journal and The Astrophysical Journal Letters, respectively.

Hunting for Elusive Companions

Only about one percent of stars host massive planets or brown dwarfs that can be photographed directly with today’s telescopes. Even in young systems where these objects still glow with heat from their formation, they remain far fainter than their host stars—requiring both ingenuity and advanced technology to detect.

OASIS identifies promising targets by analyzing measurements from the European Space Agency’s Hipparcos and Gaia missions to find “accelerating stars”—stars whose motion reveals they are being tugged by unseen companions. The Subaru Telescope’s extreme adaptive optics system, SCExAO, then captures high-contrast images of these hidden worlds, while follow-up observations using Keck Observatory’s NIRC2 camera provide longer-wavelength measurements essential for characterizing their atmospheres and orbits.

A Rare Brown Dwarf: HIP 71618 B

The first discovery, HIP 71618 B, is a 60-Jupiter-mass brown dwarf located 169 light-years away in the constellation Bootes. Brown dwarfs, sometimes referred to as “failed stars,” form like stars but never accumulate enough mass to sustain nuclear fusion and cooler. Brown dwarfs are cooler than stars and are much fainter at visible wavelengths we can see than at longer, infrared wavelengths that can be seen with Keck Observatory and the Subaru Telescope. Data from Keck/NIRC2 and SCExAO taken within days of one another discovered this companion. Follow-up data from both Keck Observatory and the Subaru Telescope taken over the next year then revealed the companion’s orbit.

One exciting outcome of this discovery is its unique suitability for NASA’s Roman Space Telescope. Roman will conduct a technology demonstration to test coronagraph systems—tools future telescopes will depend on to image Earth-like planets that are billions of times fainter than their host stars.

Before this discovery, no confirmed object met all the strict criteria needed to validate this technology. HIP 71618 B now provides that rare target: a bright host star, an ideal separation, and a companion that will be faint enough at visible wavelengths where Roman operates to challenge and confirm the performance of its coronagraph.

“The discovery of HIP 71618 B is demonstrably suitable for the Roman Coronagraph Technology Demonstration,” said Mona El Morsy, postdoctoral researcher at The University of Texas at San Antonio and lead author of this study. “Providing a target that advances the community’s preparation for this mission is directly relevant, and I am optimistic that these discoveries will pave the way for many more systems identified through the OASIS survey.”

A New Giant Planet: HIP 54515 b

The other newly discovered companion, HIP 54515 b, is an 18-Jupiter-mass planet orbiting a star 271 light-years away in the constellation Leo. Located at a distance from its star similar to Neptune’s orbit around the Sun, the planet appears extraordinarily close to its host star as seen from Earth—comparable to the apparent size of a football viewed over 200 miles away. The Subaru Telescope’s SCExAO system delivered the ultra-sharp images needed to reveal this faint, giant planet beside its bright star.

While SCExAO imaged this planet, Keck Observatory data played a critical supporting role in interpreting it, enabling researchers to precisely model its properties and evolutionary history. “We used over a decade’s worth of data from the Keck Observatory Archive (KOA) to help precisely calibrate SCExAO”, said Currie.

Maunakea’s Enduring Legacy of Discovery

Together, these discoveries highlight the power of combining space-based precision measurements with the unparalleled imaging capabilities of Maunakea’s observatories. OASIS’s early results demonstrate how the Subaru Telescope’s SCExAO system, Keck Observatory’s high-resolution infrared imaging, and decades of archival data continue to uncover companions that would otherwise remain invisible.

“As these discoveries show, Maunakea Observatories like Keck Observatory and the Subaru Telescope remain leading engines of discovery in astronomy even 25–30 years after their construction,” said Currie. “They will be even more powerful in the near future with new instruments coming online and improvements to existing instrumentation. With improved technology serviced by a team of dedicated local staff, Keck Observatory and the Subaru Telescope will remain critical telescopes in astronomy for many, many decades to come.”

What’s Next for OASIS

The research team has uncovered additional planetary and brown dwarf companions through OASIS, which will be announced in 2026. Plans are also underway to collect new Subaru Telescope SCExAO images of HIP 71618 B and to reimage HIP 54515 b using Keck Observatory to refine the companions’ properties and orbits.

Astrobiology, Astronomy, exoplanet,