Last year, astronomers were intrigued by a fast-moving asteroid zipping through our Solar System. It sped along at about 68 kilometers per second, twice the speed at which Earth orbits the Sun. But what if something even larger and quicker—a black hole—zoomed past at around 3,000 kilometers per second? We wouldn’t even notice until its gravitational pull started affecting the paths of our outer planets.
While it might sound far-fetched, evidence suggests that runaway black holes are not just theoretical. Astronomers have observed massive black holes racing through other galaxies, hinting at the existence of smaller, less detectable ones in our cosmic neighborhood.
The concept of runaway black holes takes us back to the 1960s. New Zealand mathematician Roy Kerr solved equations from Einstein’s general relativity, revealing key insights about spinning black holes. One was the “no-hair theorem,” which states that black holes can be identified by just three traits: mass, spin, and electric charge. Kerr found that a black hole can have substantial energy in its rotation—up to 29% of its mass can be in the form of this rotational energy.
Roger Penrose, a British physicist, theorized over fifty years ago that this rotational energy can be released. Essentially, a spinning black hole functions like a super battery, capable of unleashing enormous amounts of energy. When two black holes collide, they can release this energy in a matter of seconds, often producing gravitational waves.
When LIGO and Virgo started detecting these gravitational waves in 2015, they provided tangible proof supporting many theories. They recorded the “ringdowns” of newly formed black holes, where the speed of rotation influences how long they vibrate. Observations revealed that some black holes had randomly oriented spins and significant energy reserves, reinforcing the idea that runaway black holes might actually exist.
Finding runaway black holes isn’t easy, especially the smaller ones. However, larger black holes—those with masses in the millions or billions of suns—would disrupt their surroundings as they travel through galaxies. They leave behind trails of stars, similar to how a plane leaves contrails in the sky. This process, driven by gravitational forces, can take millions of years.
In 2025, researchers published exciting findings showing straight lines of stars in several galaxies, potentially proof of runaway black holes. One study by Yale’s Pieter van Dokkum illustrated a distant galaxy captured by the James Webb telescope, showcasing a bright trail around 200,000 light years long, possibly created by a black hole 10 million times the mass of our Sun, zooming close to 1,000 kilometers per second.
Another study described a straight contrail in NGC3627, likely caused by a black hole with a mass of about 2 million suns, traveling at around 300 kilometers per second and leaving a trail roughly 25,000 light years long.
These findings raise compelling questions about the existence of smaller runaway black holes, as gravitational waves hint that even they could achieve the necessary speeds for intergalactic travel.
The idea of runaway black holes adds a thrilling layer to our understanding of the universe. While the chances of one entering our Solar System are slim, it’s a captivating concept that enriches the ongoing narrative of cosmic exploration and discovery.
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