Universe Today reported that a study led by Emma Jane Weller, an Astronomy PhD candidate at Yale University, with Priyamvada Natarajan and Colin J. Burke, was published in The Astrophysical Journal Letters. The work introduces a class of black holes that drift through space without being bound to any host galaxy. ZME Science covered the findings and Phys.org highlighted the work.
The researchers define wandering black holes as objects that are not supermassive and are not gravitationally attached to any galaxy, allowing them to travel through the cosmos for billions of years. This distinguishes them from the supermassive black holes that are at galactic centers. The description appears in coverage by Universe Today, ZME Science, Phys.org and Yahoo Tech.
To study these objects the team used ASTRID, a high‑resolution cosmological simulation suite that models the evolution of stars, dark matter, gas and black holes from the earliest epochs to the present. The simulation does not automatically place black holes at galaxy centers; instead it lets gravitational forces move them freely. This makes it possible to separate centrally located black holes from those that wander.
ASTRID followed galaxies with stellar masses ranging from ten million to one trillion solar masses and traced their development over roughly 12.6 billion years, covering most of cosmic history. This range is reported by Universe Today, ZME Science and Phys.org. The broad scope enabled the team to compare massive systems with tiny dwarf galaxies within the same framework.
Because the simulation tracks gravitational interactions, it shows that black holes become wandering more easily in low‑mass galaxies where the central pull is weaker. In massive galaxies the deep potential well tends to keep black holes near the nucleus. Universe Today, ZME Science, Phys.org and Yahoo Tech make this point.
In low‑mass galaxies that are still forming stars, black holes tend to remain off-center or travel in the halo, while those that have stopped forming stars are more likely to settle back into the galactic center. Universe Today, ZME Science, Phys.org and Yahoo Tech note this trend.
Conversely, low‑mass galaxies that have ceased forming stars are more likely to contain black holes at their centers, while star‑forming low‑mass galaxies are more likely to host wandering black holes. This result comes directly from the ASTRID output and ZME Science, Phys.org and Yahoo Tech highlight it.
Despite billions of years of mergers and accretion, dwarf galaxies preserve a memory of the mass of the black‑hole seed that formed them originally. Universe Today, ZME Science, Phys.org and Yahoo Tech all state that in massive galaxies repeated mergers tend to blur any distinction between black holes that grew from light seeds and those that arose from heavy seeds. Thus, low‑mass systems remain valuable probes of the early black‑hole population because the seed‑mass signature can survive.
The study discusses two broad routes for the first black holes: light seeds of about one hundred solar masses left by the first generation of Population III stars, and heavy seeds ranging from ten thousand to one million solar masses formed by the direct collapse of pristine gas. These ranges are cited by Universe Today, ZME Science, Phys.org and Yahoo Tech. They correspond to the observational uncertainties surrounding the origin of supermassive black holes.
In massive galaxies, billions of years of mergers and growth tend to erase differences between seed types, making it difficult to infer the original formation channel. In contrast, small galaxies may preserve the signature, allowing astronomers to use their black‑hole masses as a fossil record of the early universe.
The ASTRID model cannot reproduce genuinely light, first‑star‑scale seeds; its smallest seeds already weigh roughly forty‑four thousand to four hundred and forty thousand solar masses. This limitation is noted by ZME Science and Yahoo Tech. Therefore the simulation follows heavier seeds down to about forty‑four thousand solar masses, showing how such seeds could leave detectable traces in low‑mass galaxies.
When the analysis is limited to black holes descended from seeds heavier than one hundred thousand solar masses, the fraction of low‑mass galaxies that host them falls markedly compared with the overall black‑hole population. This drop is reported by ZME Science and indicates that counting black holes in dwarf systems can retain a memory of the original seed population.
A 2025 survey of 1,606 galaxies showed that the presence of massive central black holes drops sharply toward lower galaxy masses, with roughly one‑third of dwarf systems ranging from 100 million to 1 billion solar masses hosting such a black hole. ZME Science mentions this observational result and matches the simulation’s expectation that wandering black holes are more prevalent in low‑mass systems.
The simulations indicate that certain galaxies showing no central black hole could actually host one at a distance from the core.
Astronomers seeking wandering black holes should examine regions outside galactic centers, employing deep X‑ray imaging to spot accretion, optical and infrared spectroscopy to measure movement, radio surveys to detect jet or hot‑gas emission, and transient flares that arise when an invisible black hole shreds a passing star. Universe Today, ZME Science, Phys.org and Yahoo Tech describe this framework. Together these techniques form a way to probe black‑hole origins and their dynamical histories.
“What is exciting about our findings is that black holes seem to remember more than the circumstances of their birth.” > — Priyamvada Natarajan
The research was led by Emma Jane Weller, an Astronomy PhD candidate at Yale University, with Priyamvada Natarajan, professor of physics and chair of the astronomy department at Yale, and Colin J. Burke, a postdoctoral fellow at Yale and the University of North Texas. It was published in The Astrophysical Journal Letters. This information is provided by Universe Today, ZME Science, Phys.org and Yahoo Tech.
Low‑mass galaxies keep a memory of the mass of the black‑hole seed that formed them originally, even after billions of years of mergers and accretion. This preservation occurs because their weaker gravitational potentials allow black holes to wander, keeping the seed‑mass imprint detectable. Universe Today, ZME Science, Phys.org and Yahoo Tech highlight this aspect of the simulation results.
The study identifies two pathways for the first black holes: light seeds of roughly one hundred solar masses left by the first generation of Population III stars, and heavy seeds ranging from ten thousand to one million solar masses formed by the direct collapse of pristine gas. These ranges reflect the current uncertainty about how supermassive black holes arose in the early universe.
To spot wandering black holes, researchers can use deep X‑ray data to find accretions, optical and infrared spectroscopy to track motions, radio observations to catch jet or hot‑gas signatures, and brief flares that happen when an unseen black hole disrupts a passing star. These methods together allow a search beyond galactic nuclei.
The comment from Priyamvada Natarajan underscores that the masses and trajectories of these black holes retain information about their origins, offering a fossil record that can be deciphered with suitable observations.
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