Yale Study Traces Wandering Black Holes to Galaxy Mergers

Wandering black holes that travel through the cosmos for billions of years without being bound to any galaxy may have originated as supermassive black holes displaced from galactic centers by ancient mergers. Researchers from Yale University and the University of North Texas explored this hypothesis in a new study published in The Astrophysical Journal Letters, utilizing cosmological simulations to trace black hole evolution across 12.6 billion years.

Simulations Using the ASTRID Suite Track Black Hole Evolution Over 12.6 Billion Years

The research team employed ASTRID, a high-resolution cosmological simulation suite that models the evolution of the Universe from its earliest periods to the present day. The simulation tracks stars, dark matter, gas, and black holes across galaxies ranging in mass from 10 million to 1 trillion Solar masses. Unlike simulations that automatically place black holes at galaxy centers, ASTRID models the gravitational forces that move black holes through their surroundings. This capability allowed the team to differentiate between stable galactic-core black holes and wandering objects, revealing that the displacement process happens more frequently in low-mass galaxies where gravitational pull is weaker.

Our results show that considering wandering black holes, in addition to centered black holes, is essential for understanding the origins and dynamics of massive black holes and the histories of their host galaxies.

Emma Jane Weller

Yale Researchers Disentangle Galaxy Histories From Black Hole Locations

The study was led by Emma Jane Weller, an Astronomy PhD candidate at Yale University, alongside Professor Priyamvada Natarajan and Postdoctoral Fellow Colin J. Burke. Natarajan serves as Chair of the Yale astronomy department and a Principal Investigator with Harvard University’s Black Hole Initiative. Prevailing scientific theories suggest early black holes originated as seeds in the young Universe, though researchers debate whether they formed as small seeds left by Population III stars or heavy seeds created via direct gas collapse. Natarajan, a leading proponent of the heavy seeds theory, notes that present-day black hole locations carry the imprint of everything that has happened to their host galaxies.

What is exciting about our findings is that black holes seem to remember more than the circumstances of their birth. Their present-day locations carry the imprint of everything that has happened to their host galaxies. By separating black holes at galactic centers from those that are wandering, we can begin to disentangle these two histories. Some of the universe’s most revealing black holes may be the ones that have wandered away.

Priyamvada Natarajan

Observational Methods Planned to Probe Wandering Black Hole Populations

The ASTRID simulation also indicated that low-mass galaxies retain information about their initial seed black holes despite billions of years of growth. The findings suggest that low-mass galaxies that stopped forming stars tend to keep black holes at their centers, while galaxies still actively forming stars are more likely to host wanderers. The research team aims to combine these simulation results with deep X-ray observations, optical and infrared spectroscopy, radio astronomy, and transient flares generated when black holes consume stars to identify specific imprints of galaxy evolution.

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