In the world of black holes, there are generally three size categories: stellar-mass black holes (about five to 50 times the mass of the sun), supermassive black holes (millions to billions of times the mass of the sun), and intermediate-mass black holes with masses somewhere in between.
While we know that intermediate-mass black holes should exist, little is known about their origins or characteristics—they are considered the rare "missing links" in black hole evolution.
However, four new studies have shed new light on the mystery. The research was led by a team in the lab of Assistant Professor of Physics and Astronomy Karan Jani , who also serves as the founding director of the Vanderbilt Lunar Labs Initiative. The work was funded by the National Science Foundation and the Vanderbilt Office of the Vice Provost for Research and Innovation.
The primary paper, " Properties of 'Lite' Intermediate-Mass Black Hole Candidates in LIGO-Virgo's Third Observing Run ," was published in Astrophysical Journal Letters and led by Lunar Labs postdoctoral fellow Anjali Yelikar and astrophysics Ph.D. candidate Krystal Ruiz-Rocha. The team reanalyzed data from the Nobel-Prize winning Laser Interferometer Gravitational-Wave Observatory (LIGO) detectors in the U.S. and the Virgo detector in Italy.
The researchers found that these waves corresponded to mergers of black holes greater than 100 to 300 times the mass of the sun, making them the heaviest gravitational-wave events recorded in astronomy.
"Black holes are the ultimate cosmic fossils," Jani said. "The masses of black holes reported in this new analysis have remained highly speculative in astronomy. This new population of black holes opens an unprecedented window into the very first stars that lit up our universe."
Earth-based detectors like LIGO capture only a split second of the final collision of these "lightweight" intermediate-mass black holes, making it challenging to determine how the universe creates them. To tackle this, Jani's lab turned to the upcoming European Space Agency and NASA's Laser Interferometer Space Antenna (LISA) mission, launching in the late 2030s.
In two additional studies published in Astrophysical Journal, " A Sea of Black Holes: Characterizing the LISA Signature for Stellar-origin Black Hole Binaries ," led by Ruiz-Rocha, and " A Tale of Two Black Holes: Multiband Gravitational-wave Measurement of Recoil Kicks ," led by former summer research intern Shobhit Ranjan, the team showed LISA can track these black holes years before they merge, shedding light on their origin, evolution, and fate.
Detecting gravitational waves from black hole collisions requires extreme precision—like trying to hear a pin drop during a hurricane. In a fourth study also published in Astrophysical Journal, " No Glitch in the Matrix: Robust Reconstruction of Gravitational Wave Signals under Noise Artifacts ," the team showcased how artificial intelligence models guarantee that signals from these black holes remain uncorrupted from environmental and detector noise in the data. The paper was led by postdoctoral fellow Chayan Chatterjee and expands upon Jani's AI for New Messengers Program , a collaboration with the Data Science Institute.
"We hope this research strengthens the case for intermediate-mass black holes as the most exciting source across the network of gravitational-wave detectors from Earth to space," Ruiz-Rocha said. "Each new detection brings us closer to understanding the origin of these black holes and why they fall into this mysterious mass range."
Moving forward, Yelikar said the team will explore how intermediate-mass black holes could be observed using detectors on the moon.
"Access to lower gravitational-wave frequencies from the lunar surface could allow us to identify the environments these black holes live in—something Earth-based detectors simply can't resolve," she said.
In addition to continuing this research, Jani will also be working with the National Academies of Sciences, Engineering, and Medicine on a NASA-sponsored study to identify high-value lunar destinations for human exploration to address decadal-level science objectives.
As part of his participation in this study, Jani will be contributing to the Panel on Heliophysics, Physics, and Physical Science, to identify and articulate the science objectives related to solar physics, space weather, astronomy, and fundamental physics that would be most enabled by human explorers on the moon.
"This is an exciting moment in history—not just to study black holes, but to bring scientific frontiers together with the new era of space and lunar exploration," Jani said. "We have a rare opportunity to train the next generation of students whose discoveries will be shaped by, and made from, the moon."
