What could drive a supermassive black hole (SMBH) from its home galaxy? They can have hundreds of millions or even billions of solar masses? What is strong enough to drive away one of these giants?
The answer lies in galaxy mergers.
Astronomers have determined that this is the first confirmed case of a runaway SMBH. It is located in the Cosmic Owl galaxy, which is actually a pair of ring galaxies about 8.8 billion light-years away. The rings appear like owl eyes as they get closer to merging. Astronomers observing the Cosmic Owl found a long linear feature in the galaxy and wondered whether it could be the tail of the first confirmed runaway SMBH. Now new research confirms this.
The JWST captured these images of the Cosmic Owl. Each of the “eyes” is an active galactic nucleus (AGN), and the “beak” is a stellar chamber. Image source: Liu et al. 2025.
The new research is titled “JWST confirmation of a runaway supermassive black hole from its supersonic bow shock” and was submitted to The Astrophysical Journal Letters. The lead author is Pieter van Dokkum from the astronomy department at Yale University. Van Dokkum is the lead author of several papers examining the Cosmic Owl for clear evidence of a runaway SMBH. The research is available online at arxiv.org.
“The occasional escape of supermassive black holes (SMBHs) from their host galaxies is a long-standing prediction of theoretical studies,” write van Dokkum and his co-authors. “We present JWST/NIRSpec IFU observations of a possible runaway supermassive black hole at the tip of a 62 kpc long linear feature at z = 0.96.”
There are two channels that can give an SMBH the speed it needs to escape its galaxy. One is caused by a three-body interaction, the other is a gravitational wave recoil caused by a BH-BH merger. “Both channels form naturally as a result of galaxy mergers, as the black holes of the ancestral galaxies end up at the center of the descendant galaxies,” the authors write.
Two different characteristics play a role here. One is the tail, which is 200,000 light years long, and the other is the bow shock absorber. The pressure in the tail is lower than at the bow shock, so gas accumulates in the tail and forms new stars.
This HST image shows the tail of the runaway black hole 1 (RBH1). The tail is about 62 kpc long, or about 200,000 light years. Photo credit: van Dokkum et al. 2025.
The JWST observed the candidate Runaway Black Hole 1 (RBH1) with its NIRSpec Integrated Field Unit. This instrument observes small patches of sky in cubes of 3 arcseconds by 3 arcseconds, simultaneously capturing light and spectra. This allows astronomers to not only see objects, but also analyze light to simultaneously determine composition, temperature and motion.
“We thus find that the observed kinematics at the tip of RBH-1 are qualitatively consistent with expectations for a strong supersonic bow thrust,” the authors explain. A bow shock absorber is important evidence of an RBH. “The evidence for a supersonic bow shock at the tip of RBH-1 is very strong, almost overwhelming.”
This image is based on JWST observations of the red-shifted spectral lines OIII and H-alpha. Regarding the mean field, the authors explain: “There is a striking pattern where the emission near the tip systematically shifts further upstream at higher velocities.” On the left and right are position/velocity diagrams, also based on OIII and H-alpha. “These diagrams show a clear gradient of ∼ 600 km s−1 over ∼ 1 kpc,” the authors write. Photo credit: van Dokkum et al. 2025.
By identifying a tail and a bow shocker, researchers have confirmed that what they are seeing is the first confirmed runaway black hole. In a previous work, they identified these features, but lacked detailed evidence to confirm that what they saw was an RBH. New JWST and HST observations are largely responsible for the confirmation, with the JWST playing the leading role.
“The central suggestion of Paper I was that the linear feature is the trail behind a runaway supermassive black hole, and this is strongly supported by our analysis,” the authors write. “Using newly acquired HST/UVIS and JWST/NIRSpec data, we confirm that the remarkable linear feature reported in Article I is the trail behind a runaway SMBH.”
“We also confirm the presence of a spatially resolved bow shock at the head of the wake, something we predicted based on shock models and wake luminosity.” [O III] Nodes in the Keck/LRIS data,” the authors write in their conclusion.
It has been 50 years since scientists predicted that SMBHs could spin out of control due to gravitational wave recoil or three-body interaction. Finding the first is always a triumph of determination and intellectual prowess, but where there is one, there are likely to be others. Finding them will be the task of future telescopes.
“The most obvious data sets to systematically search for these features are large-scale studies using Euclid and Roman,” the authors conclude.
The universe can sometimes seem like a terribly strange and threatening place, and this discovery will not allay fears. Even if we’re not in any danger at all, it’s a terrifying realization that supermassive black holes with tens of millions of solar masses can rocket through space, compressing everything in front of them and dragging a stream of gas and new stars with them.
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