Black holes move through space just like stars, planets, and every other massive object in the universe. They orbit, drift, get yanked by gravity, and sometimes get launched at tremendous speeds. The Milky Way’s own central black hole, Sagittarius A*, orbits more or less at rest relative to the galaxy’s center, but other black holes race through space at hundreds or even thousands of kilometers per second. The ways black holes travel range from the mundane (simple orbital motion) to the dramatic (getting kicked by gravitational waves at a fraction of the speed of light), and astronomers have now observed some of these scenarios directly.
Sagittarius A* and the Quiet Center
The most precisely tracked black hole in the universe is the one at the center of our galaxy. Sagittarius A* (Sgr A*) is roughly four million times the mass of our Sun, and it has been monitored for decades using radio telescopes and infrared observations. Very Long Baseline Array measurements spanning 18 years found that Sgr A* appears to move across the sky at about 6.4 milliarcseconds per year along the galactic plane, but almost all of that apparent motion comes from our own Sun orbiting around the galactic center. Once you subtract the Sun’s motion, the leftover velocity of Sgr A* itself is tiny: less than about 1 kilometer per second in any direction.1The Astrophysical Journal. The Proper Motion of Sagittarius A*. III. The Case for a Supermassive Black Hole More recent work has refined this further by tying Keck adaptive optics observations to the Gaia reference frame, which is anchored to distant quasars and provides an essentially “absolute” coordinate system.2The Astrophysical Journal. Absolute Motion of the Infrared Counterpart to Sagittarius A* in the Gaia Celestial Reference Frame 3 and Limits on an Intermediate-mass Black Hole Companion
This near-stillness makes physical sense. Sgr A* is the most massive single object in the Milky Way’s core, so all the surrounding stars orbit around it rather than the reverse. Think of it as a bowling ball sitting at the bottom of a funnel: lighter objects roll around it, and only an extremely forceful event could dislodge it. That said, “near-stillness” is relative to the galaxy. Sgr A* is still hurtling through the universe along with the entire Milky Way, which moves at several hundred kilometers per second relative to the cosmic microwave background. In other words, the black hole isn’t stationary in any absolute sense; it just happens to sit calmly at the gravitational anchor point of its host galaxy.
Born With a Kick
Not every black hole enjoys such a peaceful existence. Stellar-mass black holes, the ones that form when massive stars die, often begin their lives moving fast. When a star collapses and explodes as a supernova, the explosion is rarely perfectly symmetric. The slight imbalance in which direction material gets flung can impart a “natal kick” to the newborn compact remnant, sending it flying through space. Neutron stars are well known for receiving natal kicks of hundreds of kilometers per second, and evidence is mounting that many black holes get them too.
A study of the X-ray binary AT2019wey, which contains a stellar-mass black hole, found that the system’s current velocity and position above the plane of our galaxy point to a natal kick delivered during a supernova explosion rather than a gentler process called direct collapse.3The Astrophysical Journal. Proper Motion and Natal Kick in the Galactic Black Hole X-Ray Binary AT2019wey The distinction matters: if a dying star collapses straight into a black hole without a violent explosion, most of the energy escapes as neutrinos, and any resulting kick comes only from tiny asymmetries in neutrino emission, producing a much smaller push.4Astronomy & Astrophysics. The impact of natal kicks on black hole binaries But when the collapse does involve a supernova, the kick can be substantial enough to send the black hole cruising through the galaxy on a trajectory very different from where its parent star lived.
These natal kicks have a lasting effect on what astronomers observe. A strong kick can break apart a binary star system, sending the newly formed black hole off on its own. A milder kick might keep the binary intact but alter its orbit. The population of black hole binaries we detect with X-ray telescopes is shaped by these kicks, since the systems that survived had to absorb the impact without flying apart.
Wandering Alone Through the Galaxy
Many black holes are not in binary systems at all. They drift through the galaxy in isolation, invisible to conventional telescopes because a lone black hole doesn’t emit light. The only practical way to spot one is gravitational microlensing: when such a black hole passes between us and a distant background star, its gravity bends the star’s light, briefly magnifying and deflecting it. In 2022, a team using the Hubble Space Telescope reported the first unambiguous detection of an isolated stellar-mass black hole through this technique, observing the long-duration microlensing event known as MOA-2011-BLG-191/OGLE-2011-BLG-0462.5The Astrophysical Journal. An Isolated Stellar-mass Black Hole Detected through Astrometric Microlensing Follow-up observations over six years confirmed the result and solidified it as the first and only unambiguously identified isolated stellar-mass black hole to date.6The Astrophysical Journal. OGLE-2011-BLG-0462: An Isolated Stellar-mass Black Hole Confirmed Using New HST Astrometry and Updated Photometry
These solitary black holes are thought to be common. Theoretical estimates suggest the Milky Way could harbor on the order of a hundred million stellar-mass black holes, most of them completely dark and drifting. The fact that we’ve only confirmed one says more about how hard they are to find than how rare they are. Each is following its own orbit through the galaxy, influenced by the combined gravitational pull of all the surrounding matter, occasionally making its presence felt through brief lensing events as it drifts in front of a background star.
Dynamical Friction and the Slow Drag Toward the Center
When a heavy object moves through a sea of lighter objects, something interesting happens. The heavy object’s gravity pulls nearby stars (or dark matter particles) toward it, creating a temporary overdensity behind it, like a gravitational wake. That trailing clump of matter then tugs backward on the heavy object, gradually slowing it down. This effect, called dynamical friction, was first described by Subrahmanyan Chandrasekhar in 1943, and it plays a crucial role in how supermassive black holes end up at the centers of galaxies.
After two galaxies merge, each one’s central supermassive black hole is left orbiting somewhere in the combined stellar system. Dynamical friction drags each black hole inward, transferring its orbital energy to the surrounding stars and causing it to spiral toward the center of the merged galaxy.7Monthly Notices of the Royal Astronomical Society. Rapid sinking and efficient mergers of supermassive black holes in compact high-redshift galaxies The timescale for this sinking depends on the mass of the black hole, the density of the surrounding stellar environment, and the structure of the galaxy’s core. In dense, compact galaxies at high redshift, the process can happen quickly.8Monthly Notices of the Royal Astronomical Society. High-redshift supermassive black hole mergers in simulations with dynamical friction modelling In more diffuse environments, it can stall: if the core of the galaxy has too few slow-moving stars for the black hole to interact with, the drag effectively weakens, and the black hole can get stuck in orbit at a distance of a few parsecs from the center rather than reaching it.9The Astrophysical Journal. Dynamical Friction around Supermassive Black Holes
This stalling problem, sometimes called the “last parsec problem,” is an active area of research. Simulations suggest that in realistic galaxies, additional effects like the galaxy’s rotation, gas dynamics, and repeated interactions with individual stars eventually finish the job and bring the two black holes close enough to form a gravitationally bound binary.
When Galaxies Merge, Black Holes Follow
Galaxy mergers are the main pathway by which supermassive black holes end up near each other. When two galaxies collide, their stars mostly sail past one another because the distances between stars are vast. But the two central black holes, each embedded in its own dense stellar core, are gradually funneled inward by dynamical friction as described above. If both black holes are actively swallowing gas during this process, astronomers can observe the pair as a dual active galactic nucleus, with two bright points visible in X-ray, optical, or radio images.10arXiv. Dual Active Galactic Nuclei in Nearby Galaxies
Candidate dual and binary supermassive black holes have been identified through velocity offsets in the broad emission lines of quasars. When the broad-line region of an active black hole is moving relative to its host galaxy’s rest frame, the spectral lines appear Doppler-shifted, and this shift can be interpreted as evidence of a binary or a recoiling black hole. Deep Chandra X-ray observations of quasars with such velocity offsets are helping astronomers distinguish between genuine binary systems, recoiling remnants, and more mundane explanations involving gas dynamics around a single black hole.11The Astrophysical Journal. Chandra X-Ray Observations of Quasars with Velocity-offset Broad Lines: Assessing the Binary Supermassive Black Hole Hypothesis
Gravitational Wave Recoil
The most violent way a black hole can be set in motion is through the merger process itself. When two black holes spiral together and merge, they radiate gravitational waves. If the merger is perfectly symmetric, those waves carry energy equally in all directions and the remnant black hole stays put. But real mergers are almost never perfectly symmetric. Differences in the masses and spins of the two black holes mean the gravitational waves are radiated more strongly in some directions than others. The resulting imbalance acts like a rocket exhaust, delivering a recoil kick to the newly formed remnant.
The theoretical maximum for these kicks is extreme. A massive set of 1,381 numerical relativity simulations exploring high-energy black hole collisions found that in the most favorable spin configurations, the recoil velocity can reach roughly 28,500 kilometers per second, about 10 percent of the speed of light.12PubMed. Ultimate Black Hole Recoil: What is the Maximum High-Energy Collision Kick? In practice, kicks this large require extreme conditions that are unlikely in nature, but kicks of hundreds to thousands of kilometers per second are expected to be common outcomes of real mergers.
Observational evidence is starting to catch up with theory. Analysis of the gravitational wave signal from the merger event GW200129 found evidence of strong orbital precession, and models constrained the remnant’s kick velocity to roughly 1,500 kilometers per second, with a lower bound of about 700 kilometers per second at 90 percent credibility.13PubMed. Evidence of Large Recoil Velocity from a Black Hole Merger Signal Future space-based gravitational wave detectors are expected to measure kicks as low as about 500 kilometers per second for supermassive black hole mergers, which would be a common outcome following galaxy mergers.14PubMed. Black Hole Kicks as New Gravitational Wave Observables These measurements won’t just detect the final speed; they’ll track how the kick builds up during the final orbits, using the Doppler shift of the gravitational waves themselves.
Ejected From Star Clusters
Gravitational wave recoil isn’t the only way a black hole gets launched. In dense star clusters, three-body interactions can catapult black holes out entirely. When a compact binary (say, two black holes orbiting each other tightly) encounters a third object, the encounter transfers energy from the binary’s internal orbit to the kinetic energy of the participants. If the recoil velocity exceeds the cluster’s escape speed, the binary and the interloper both get ejected.15Astronomy & Astrophysics. Eccentric black hole mergers via three-body interactions in young, globular, and nuclear star clusters
This matters because it affects where black hole mergers take place. A binary that gets kicked out of a globular cluster will merge in isolation, far from any stars, whereas one that stays inside the cluster might undergo further encounters that change its orbit before the merger happens. The escape velocity of a typical globular cluster is on the order of tens of kilometers per second, which is low enough that many dynamically formed binaries do get ejected. Nuclear star clusters, which sit at the centers of galaxies and are much more massive, have higher escape speeds and can retain more of their black holes. The type of cluster environment shapes the population of merging black holes that gravitational wave detectors eventually pick up.
The Runaway Black Hole Caught in the Act
In 2025, astronomers used the James Webb Space Telescope to confirm one of the most dramatic examples of a moving black hole ever observed: a supermassive black hole racing through intergalactic space at roughly 950 kilometers per second, leaving a 62-kiloparsec-long trail of shocked gas behind it. The object, at a redshift of 0.96, had been a puzzle since its initial discovery because of its peculiar linear feature stretching away from a galaxy. JWST’s infrared spectroscopy revealed a sharp velocity jump of about 600 kilometers per second at the feature’s tip, exactly what you’d expect from a supersonic bow shock.16The Astrophysical Journal Letters. JWST Confirmation of a Runaway Supermassive Black Hole via Its Supersonic Bow Shock
The velocity along the wake decreases smoothly from about 300 kilometers per second near the tip to about 100 kilometers per second closer to the former host galaxy, a pattern explained by the shocked gas gradually mixing with the surrounding medium through turbulent entrainment. The emission-line ratios at the tip match expectations for fast radiative shocks, and energy conservation over the lifetime of the wake suggests the black hole’s mass is at least ten million solar masses.17arXiv. JWST Confirmation of a Runaway Supermassive Black Hole via its Supersonic Bow Shock The researchers concluded that the wake is powered by a supersonic runaway supermassive black hole, a scenario long predicted as a consequence of either gravitational-wave recoil or multibody ejection from a galactic nucleus. Seeing it confirmed observationally was a milestone.
What makes this object so striking is that the black hole didn’t just leave its galaxy quietly. As it plows through the diffuse gas between galaxies, it compresses the gas ahead of it hard enough to trigger star formation in its wake. It’s simultaneously destroying and creating: ripped from its home galaxy by an enormous kick, it drags enough material and energy with it to light up a trail visible across cosmic distances.
What Happens to the Disk After a Kick
A natural question about recoiling black holes is whether they take their surrounding material with them. When a supermassive black hole is actively feeding, it’s surrounded by an accretion disk of hot gas. Simulations of merging supermassive black hole binaries show that even after a kick of about 1,000 kilometers per second, the entire surrounding disk can remain gravitationally bound and move with the remnant.18arXiv. Accretion, Jets, and Recoil in a Merging Supermassive Black Hole Binary: A Prompt Electromagnetic Postmerger Counterpart for LISA In one simulation, the newly merged and recoiling black hole even re-launched a relativistic jet aligned with its spin axis shortly after coalescence. This means a kicked black hole doesn’t go dark after ejection; it can continue glowing as an active galactic nucleus as it travels, potentially making it detectable as an off-center or intergalactic point source. The prospect of catching such objects has astronomers excited for the era of combined gravitational-wave and electromagnetic observations.
Primordial Black Holes and Cluster Dynamics
Stellar-mass and supermassive black holes aren’t the only types that move. Primordial black holes, which may have formed from density fluctuations in the very early universe, would also travel through space. If they exist, they’d behave gravitationally like any other compact mass. Theoretical work suggests primordial black holes could have formed accompanied by ultradense dark matter halos, tiny but extraordinarily dense clumps that formed at very high redshifts.19Monthly Notices of the Royal Astronomical Society. Ultradense dark matter haloes accompany primordial black holes These halos would orbit and interact with each other just as stellar-mass black holes do in clusters.
Clusters of primordial black holes, if they formed, would be subject to disruption by encounters with stars, molecular clouds, and other massive structures in the galaxy. The vulnerability of such a cluster depends on its internal binding energy and the relative velocity of whatever it encounters. For clusters with masses around a million solar masses, peak disruption occurs at relative velocities of roughly 12 to 16 kilometers per second, which is well within the range of velocities found in the Milky Way’s disk and bulge.20Monthly Notices of the Royal Astronomical Society. Do Primordial Black Hole Clusters Survive the Galaxy? Collisional Disruption and Microlensing Implications This means that if primordial black hole clusters once existed in the galaxy, many of them would have been torn apart by now, scattering their individual members into the general galactic population of dark, drifting compact objects. Whether primordial black holes actually exist remains unconfirmed, but the physics of how they’d move and interact is well understood in principle.
How Fast Can a Black Hole Possibly Travel
The speed limits depend on the mechanism. For natal kicks from supernovae, typical velocities are tens to a few hundred kilometers per second. For three-body ejections from star clusters, the speed is capped by the energy available in the binary’s orbit, usually producing kicks of tens of kilometers per second. Gravitational wave recoil can reach much higher: measured or inferred kicks for astrophysically plausible mergers range from several hundred to about 1,500 kilometers per second, with theoretical models predicting kicks up to about 5,000 kilometers per second for mergers involving rapidly spinning black holes with unfavorable spin orientations.13PubMed. Evidence of Large Recoil Velocity from a Black Hole Merger Signal The extreme upper bound of roughly 28,500 kilometers per second from high-energy collision simulations sits at about 10 percent the speed of light, but this requires maximally spinning black holes colliding under conditions unlikely to occur in nature.12PubMed. Ultimate Black Hole Recoil: What is the Maximum High-Energy Collision Kick?
Whether a kicked black hole actually escapes its galaxy depends on the competition between its velocity and the galaxy’s escape speed. A large elliptical galaxy might have an escape velocity above 1,000 kilometers per second at its center, while a dwarf galaxy could have one below 100 kilometers per second. A kick that would barely register in a giant galaxy could easily send a black hole sailing out of a dwarf. This means gravitational wave recoil is especially consequential for small galaxies, which might have trouble retaining their central black holes after mergers. Some models of galaxy evolution suggest this could explain why certain dwarf galaxies appear to lack central black holes entirely, while others retain them: the outcome hinges on the spin geometry of the final merger.