JWST Confirmation of a Runaway Supermassive Black Hole via its Supersonic Bow Shock

We present JWST/NIRSpec IFU observations of a candidate runaway supermassive black hole at the tip of a 62 kpc-long linear feature at z=0.96. The JWST data show a sharp kinematic discontinuity at the tip, with a radial velocity change of $\approx 600$ km/s across 0.1’’ (1 kpc). The velocity gradient, together with the projected post-shock flow velocity of $\approx 300$ km/s, is well described by a simple shock-compression model of a supersonic object, with a velocity of $v_{BH} = 954^{+110}{-126}$ km/s and an inclination $i=29^{+6}{-3}$ deg. The previously puzzling kinematics along the linear feature, with the observed radial velocity decreasing from $\approx 300$ km/s near the tip to $\approx 100$ km/s closer to the former host galaxy, are naturally explained as gradual downstream mixing of shocked gas with the circumgalactic medium through turbulent entrainment. The bow shock interpretation is further supported by the morphology of the gas at the tip of the wake and an analysis of the [OIII]/H$α$, [NII]/H$α$, [SII]/H$α$, and [SIII]/[SII] line ratios. The line ratios are consistent with fast radiative shocks and rapid cooling, with best-fit shock velocities that are in agreement with expectations from the black hole velocity and the shock geometry. Energy conservation over the lifetime of the wake suggests a SMBH mass of $M_{BH} \gtrsim 10^7$ M$_{\odot}$. These results 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.

💡 Research Summary

The authors present a decisive confirmation that the 62 kpc linear feature (RBH‑1) discovered in HST imaging at redshift z = 0.96 is the wake of a supersonic runaway supermassive black hole (SMBH). Using JWST/NIRSpec integral‑field spectroscopy, they obtained spatially resolved spectra of the tip of the feature and the downstream region. The data reveal a sharp kinematic discontinuity: across a projected distance of 0.1″ (≈1 kpc) the line‑of‑sight velocity jumps by ~600 km s⁻¹, while the post‑shock flow downstream shows a more modest ~300 km s⁻¹ motion. By fitting a simple shock‑compression model to the observed velocity gradient, they infer a true black‑hole speed of v_BH = 954^{+110}{-126} km s⁻¹ and an inclination of i = 29^{+6}{-3}° relative to the plane of the sky.

Morphologically, the summed