JWST observations confirm RBH‑1 as the first verified runaway supermassive black hole. Located about 7.5 billion light‑years away and weighing at least 10 million Suns, RBH‑1 is speeding at ~954 km/s (≈593 miles/second) and carving a bow shock with a 200,000‑light‑year star‑forming wake. NIRSpec spectroscopy detected a sharp 600 km/s velocity jump across the shock, and the team favors gravitational‑wave recoil from a black hole merger as the most likely cause. The finding validates long‑standing predictions that merged supermassive black holes can be ejected from their host galaxies.
JWST Confirms First Runaway Supermassive Black Hole — RBH‑1 Ejected at 954 km/s
The new JWST observations homed in on the bow shock at the front of the structure. (van Dokkum et al., arXiv, 2025)
A rare cosmic speedster has been confirmed: astronomers report that a supermassive black hole of at least 10 million solar masses has been ejected from its host galaxy and is racing through space at roughly 954 kilometers per second (about 593 miles per second), or ~0.32% of the speed of light. The source, now designated RBH-1, lies roughly 7.5 billion light‑years away and produces a pronounced bow shock plus a 200,000‑light‑year trail of star formation.
How JWST Made the Measurement
Led by Pieter van Dokkum (Yale University), the research team used the James Webb Space Telescope's near‑infrared spectrograph (NIRSpec) to map the velocity field across the bow shock where RBH‑1 plows into the galaxy's tenuous circumgalactic gas. The geometry of the system — with the black hole slightly nearer to us and the long stellar wake tilted away — enabled precise measurements of emission from shock‑heated gas on both sides of the shock front.
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Clear Spectral Signature
Spectroscopy reveals a sudden velocity jump: gas immediately behind the shock is about 600 km/s faster than gas ahead of it, while material at the outer edges of the bow shows a redshift as it streams away from the observer. This abrupt velocity contrast, together with the shape and extent of the bow shock and wake, can be explained only by a massive object moving supersonically through the circumgalactic medium at ~954 km/s.
What Launched RBH‑1?
How a supermassive black hole acquires such a powerful kick is a central question. The team considered multi‑body gravitational interactions but, with the improved JWST data, they favor a gravitational recoil produced during the merger of two supermassive black holes. In that scenario, asymmetric emission of gravitational waves at the moment of coalescence imparts momentum to the merged remnant, launching it out of the galactic nucleus.
A diagram of the geometry of a shock front. (van Dokkum et al., arXiv, 2025)
According to the authors' preprint on arXiv, the observations "confirm that the wake is powered by a supersonic runaway supermassive black hole, a long‑predicted consequence of gravitational‑wave recoil or multi‑body ejection from galactic nuclei."
Why This Matters
RBH‑1 is the first confirmed runaway supermassive black hole and provides direct observational validation of a decades‑old theoretical prediction. The discovery supports numerical simulations that predict a population of rogue supermassive black holes wandering intergalactic space after galaxy mergers and gravitational‑wave‑driven recoils. The measured speed and the mass of the host galaxy match theoretical models of recoil after binary mergers.
The team's velocity maps and analysis are available in a preprint on the arXiv server. RBH‑1 opens a new window onto violent galactic interactions, gravitational waves in the deep past, and the demographics of displaced black holes in the Universe.
