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Galaxies can grow through their mutual gravitational attraction andsubsequent union. While orbiting a regular high-surface-brightness galaxy, thebody of a low-mass galaxy can be stripped away. However, the stellar heart ofthe infalling galaxy, if represented by a tightly-bound nuclear star cluster,is more resilient. From archival Hubble Space Telescope images, we havediscovered a red, tidally-stretched star cluster positioned ~5 arcseconds (~400pc in projection) from, and pointing toward the center of, the post-mergerspiral galaxy NGC 4424. The star cluster, which we refer to as `Nikhuli', has anear-infrared luminosity of (6.88+/-1.85)x10^6 L_{solar,F160W} and likelyrepresents the nucleus of a captured/wedded galaxy. Moreover, from our ChandraX-ray Observatory image, Nikhuli is seen to contain a high-energy X-ray pointsource, with L_{0.5-8 keV} = 6.31^{+7.50}_{-3.77}x10^{38} erg/s (90%confidence). We argue that this is more likely to be an active massive blackhole than an X-ray binary. Lacking an outward-pointing comet-like appearance,the stellar structure of Nikhuli favors infall rather than the ejection from agravitational-wave recoil event. A minor merger with a low-mass early-typegalaxy may have sown a massive black hole, aided an X-shaped pseudobulge, andbe sewing a small bulge. The stellar mass and the velocity dispersion of NGC4424 predict a central black hole of (0.6-1.0)x10^5 M_solar, similar to theexpected intermediate-mass black hole in Nikhuli, and suggestive of a blackhole supply mechanism for bulgeless late-type galaxies. We may potentially bewitnessing black hole seeding by capture and sinking, with a nuclear starcluster the delivery vehicle.

Potential Black Hole Seeding of the Spiral Galaxy NGC 4424 via an Infalling Star Cluster