The Universe Fridays March 13, 2026 5 min read Add Us On Google Add SciAm Have astronomers found a runaway monster black hole or just a very weird galaxy? Despite years of debate and follow-up studies, an odd streak of cosmic light still defies a final explanation. Is it a giant black hole screaming through intergalactic space? By Phil Plait edited by Lee Billings This artist’s concept shows a runaway supermassive black hole plowing through intergalactic space. Newborn stars trail in its wake, formed from the black hole’s compression of tenuous gas in front of it. NASA, ESA, Leah Hustak (STScI) Stay connected to The Universe: Get email alerts for this weekly column by Phil Plait Enter your email I agree my information will be processed in accordance with the Scientific American and Springer Nature Limited Privacy Policy . We leverage third party services to both verify and deliver email. By providing your email address, you also consent to having the email address shared with third parties for those purposes. Sign Up There is something inherently terrifying about a supermassive black hole hurtling through space at an excess of three million kilometers per hour. Normally these behemoths squat at the centers of galaxies and for good reason; they’re usually the single most massive objects in their host galaxy and thus aren’t easily budged. But then there’s RBH-1. As a hint, the acronym “RBH” stands for “runaway supermassive black hole,” and this object may be just that: a monster some tens of millions of times the sun’s mass hauling astronomically through intergalactic space at mind-crushing speed. On supporting science journalism If you're enjoying this article, consider supporting our award-winning journalism by subscribing . By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today. Or it may just be a weird galaxy. This uncertainty may be the oddest part of the whole story: not that a runaway giant black hole might exist but that the data are so ambiguous that we can’t be sure what we’re really seeing. Even more fun, astronomers discovered RBH-1 by accident! They were examining routine Hubble Space Telescope observations of a nearby dwarf galaxy when they spotted something peculiar : a long, linear streamer of light aligned with a distant galaxy. Follow-up observations that obtained and analyzed this structure’s spectrum—its brightness versus color, which can reveal a host of information about the emitting object —revealed it to be about 7.7 billion light-years away from Earth. This means it’s quite large, approximately 200,000 light-years in length—about twice the width of our Milky Way galaxy. The spectrum also shows the structure is a mix of gas and stars and suggests that the far end is a bright knot of gas glowing as bright as nearly 50 million suns. The discovery team came up with several interpretations for the structure, including debris from a galaxy collision, gas stripped from a high-velocity galaxy moving through the tenuous intergalactic medium, and more. But the researchers concluded the best explanation was that the object is a runaway supermassive black hole that was ejected from the nucleus of a galaxy and has been trailing a wake of material as it plows through space. This may seem far-fetched, given that giant black holes aren’t known for going on walkabouts. Amazingly, however, there are several ways to eject a black hole, even one so gargantuan. For example, when two galaxies collide, their black holes can fall toward each other and eventually merge. When this happens, a truly staggering amount of energy is released as gravitational waves in a pulse so powerful that it can briefly be thousands of times more energetic than all the stars in the observable universe combined . If that energy is not released symmetrically—for example, if the colliding black holes’ spins aren’t aligned with the plane of their mutual orbit—it can give a ridiculously strong kick to the resulting merged black hole, which is then ejected from the galaxy at high speed. It’s also possible that, during a particularly complex three-way galaxy collision, all three black holes interact gravitationally, resulting in two forming a tight binary system while the third is flung away. So this idea isn’t as goofy as it initially seems. The astronomers presented evidence supporting their conclusion as well. Almost immediately, that finding was called into question, however. Another team of astronomers published a different conclusion : the structure is actually an exceptionally flat “bulgeless” galaxy; that is, a disk galaxy that is similar to our Milky Way but lacks a central bulge of old stars . Such galaxies are rare but not unknown. Seen edge on, such a galaxy would appear as a th