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Wandering black holes can preserve clues about how their host galaxies formed and changed. Their locations, motions and occasional flares may reveal how black holes grew, how galaxies assembled, and what kinds of black-hole seeds existed. The evidence combines simulations with a small number of observations; it is not yet a complete census.
What makes a black hole a “wanderer”?
“Wandering” describes a black hole’s position or motion, not a single kind of object or a single origin. The term can refer to an isolated stellar-mass black hole moving through a galaxy, or to a more massive black hole displaced from the center of a galaxy or its dark matter halo. Those cases have different formation histories and are found with different methods.
Many galaxies host a supermassive black hole at or near their center, but a black hole need not remain there. A black hole can be offset from the galaxy’s central region, and some stellar-remnant black holes roam without a bright source of matter around them. The word alone does not tell astronomers how massive an object is, why it moved, or whether it formed in the early universe.
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Black holes and galaxies grow together through processes such as mergers and the accretion of matter. When galaxies assemble, their black holes may also be displaced or left outside the new system’s center. The number and distribution of those off-center objects can therefore offer evidence about a host’s past assembly, as well as about how and when black holes formed.
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That record is indirect. A simulation can connect a population of wandering black holes to a particular model of galaxy formation, but it does not establish that every observed galaxy followed that history. Astronomers compare predictions with observations to test which formation scenarios are plausible.
Galaxy mergers can displace black holes
As galaxies merge, their black holes can end up away from the center of the combined system. The details depend on how the galaxies and their dark matter halos assembled. The offset and environment of a black hole may thus help researchers reconstruct aspects of that process.
Stellar explosions can give black holes a kick
Some stellar-mass black holes form when massive stars collapse. If the explosion that accompanies the collapse is asymmetric, the remnant can receive a kick and move through its galaxy. This is a different route to wandering from the displacement of a supermassive black hole during galaxy assembly.
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What simulations predict—and what they do not prove
Simulations help estimate how many wandering black holes might exist and where they might be found, including objects too faint to detect directly. Their results depend on how a study defines a wanderer, how black-hole seeds form, and how the model handles the dynamics of black holes and their host galaxies. Predictions should not be mistaken for observed population counts.
Romulus: a modeled population across cosmic time
A 2021 Romulus collaboration study allowed black holes to evolve dynamically instead of fixing them at the centers of their halos. In that simulation, wandering-black-hole counts scaled roughly with halo mass, and cluster-sized halos contained thousands. The study also estimated that wanderers contributed around 10 percent of the local black-hole mass budget when seed masses were included. At redshift z ≳ 4, the simulated wanderers outweighed and outshone central supermassive black holes.
These are results of the Romulus model, not universal measurements. The redshift result concerns the simulated population at an earlier stage of cosmic history; it does not mean that wandering black holes generally outshine central ones in the nearby universe.
ASTRID: possible links to low-mass galaxies
A 2026 account of findings from the ASTRID cosmological simulation reported that black holes in lower-mass galaxies were more likely to wander. The researchers suggested that the locations and abundance of those objects could retain information about black-hole seed populations and the histories of their host galaxies. The same account reported an association between central black holes and earlier cessation of star formation in low-mass galaxies.
That association does not show that central black holes caused star formation to stop, nor does the simulation prove that a particular wandering black hole reveals a unique seed or galaxy history. It describes a relationship within a modeled cosmic population. The news account identified a journal publication date of September 7, 2026, and quoted the study team; the findings should be understood as reported simulation research.
How astronomers find black holes away from galactic centers
A black hole can be difficult to see when it is not actively pulling in gas and dust. Astronomers can instead look for effects on nearby or background objects. Two approaches in the reports below—tidal disruption flares and gravitational microlensing—detect different phenomena and are not interchangeable.
Tidal disruption flares reveal some massive black holes
If a star passes close enough to a black hole, tidal forces can tear it apart. The resulting flare can make an otherwise hard-to-see black hole visible, including one far from a galaxy’s nucleus. In July 2026, NASA reported that an AI system flagged an unusual flare in data from the Zwicky Transient Facility, and follow-up observations with Swift supported the interpretation. NASA described the associated wandering black hole as having roughly a million solar masses.
NASA’s report also quoted Robert Stein, a research fellow at the University of Maryland and NASA’s Goddard Space Flight Center: “We were looking for these star-shredding events as a way to find otherwise invisible supermassive black holes wandering away from the galactic cores where they usually reside.” Stein said the discovery was “one of just a couple that have been confirmed so far,” characterizing the technique as a way to hunt for more—not as evidence of how common these objects are.
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Microlensing can expose an isolated stellar-mass black hole
An isolated stellar-mass black hole may emit little or no detectable light. Its gravity can still bend and magnify the light of a more distant background star. That brief change is called a microlensing event. NASA has described using long-term Hubble astrometry—the precise measurement of a star’s position over time—to study such an event and infer the black hole’s properties.
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This method detects a black hole’s gravitational effect on background starlight; it does not rely on a star being torn apart or on a bright accretion flare. It is therefore suited to a different kind of wandering object than the tidal-disruption searches for massive black holes.
Two reported off-center examples are separate discoveries
NASA has also reported the off-center tidal disruption event AT2024tvd, located about 2,600 light-years from its host galaxy’s central black hole, which has a mass of roughly 100 million Suns. This event is distinct from the separate 2026 report of a flare associated with a roughly million-solar-mass wandering black hole. The examples show that flares can identify black holes away from a galaxy’s center; they do not establish how frequently such objects occur.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Wandering black holes are not the same as primordial black holes
Primordial black holes are hypothetical objects proposed to have formed during the first second after the Big Bang. Their existence has not been definitively established. A primordial black hole could also be wandering, but an off-center location or a lensing signal by itself does not show that an object has primordial origins.
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How to interpret a claim about a wandering black hole
When comparing a reported discovery with a simulation, check what kind of object and evidence the claim actually concerns. These distinctions help prevent a prediction for one population from being treated as a measurement of another.
- Mass class: Is it a stellar-mass remnant or a supermassive black hole?
- Reference point: Is the object offset from the galaxy’s center, the halo’s center, or both?
- Host and era: What is known about the host galaxy’s mass and the object’s redshift?
- Proposed origin: Is the explanation a stellar-remnant kick, displacement during galaxy assembly, or the separate hypothesis of a primordial black hole?
- Evidence type: Is the claim based on a simulation, a microlensing measurement, or a tidal disruption flare?
- Evidence status: Is it a model prediction, a candidate, or a confirmed observation?
Keeping those distinctions clear matters because a simulation can predict a large hidden population while observations confirm only a few individual objects. Together, the two kinds of evidence can test ideas about black-hole seeds and galaxy histories, but neither alone provides a complete account of the population.
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