The James Webb Space Telescope spotted a luminous streak in a distant galaxy, like the wake of a speedboat, only two hundred thousand light-years long. At the head of this trail races a supermassive black hole, plowing through tenuous gas at 954 km/s. The gas gets compressed, heats up, and glows. Spectral decomposition (spectroscopy) confirmed: it's a shock wave from the runaway hole.
What kicked out this behemoth weighing millions of suns? Most likely, a gravitational kick. When two galaxies merge, their central black holes combine, emitting gravitational waves — ripples in spacetime. Uneven emission of the waves gives the merged black hole a powerful shove, like the recoil of a cannon. An alternative: the hole got spun out of a star cluster.
Supermassive black holes weigh as much as millions of Suns, yet a gravitational kick can accelerate them to the speed of an artillery shell. An encounter with such a runaway would spell catastrophe for a planetary system: orbits would shatter, and planets would fly off into the black void.
Unlike the serene black hole in Interstellar, real-life giants sometimes become cosmic projectiles, launched by a gravitational kick into intergalactic wanderings.