Black holes may grow quietly alongside galaxies even without violent mergers

For decades, the story of black hole growth has been a tale of violence—galaxies crashing together, gas funneled chaotically into the abyss, stars torn apart in gravitational tantrums. The central bulge of a galaxy was thought to be the scar tissue of such mergers, and its presence was almost a prerequisite for a supermassive black hole to thrive. But this new DESI analysis flips that script. If bulgeless galaxies—smooth, undisturbed spirals and disks—can grow black holes just as effectively, then the engine of cosmic growth might be far more mundane and mysterious: slow, steady accretion of gas, a quiet feeding that happens everywhere, all the time. What makes this deeply weird is the implication for co-evolution. We've long assumed that black holes and their host galaxies grow in lockstep, each merger event synchronizing their fates. But if a galaxy with no bulge—no record of past collisions—can harbor a black hole that's just as hefty as one in a merger-scarred galaxy, then the correlation between bulge mass and black hole mass may be a coincidence of timing, not a causal chain. It's like discovering that two strangers who've never met share the same heartbeat. The universe is full of such hidden harmonies, and this one suggests that black holes are less like apex predators requiring chaos to thrive, and more like patient gardeners, slowly cultivating their growth over eons. This also raises a tantalizing question: what exactly *is* a bulge, then? If it's not the necessary scaffolding for black hole growth, perhaps bulges are simply one possible outcome of a galaxy's life, not a prerequisite. The 546 bulgeless galaxies in this sample are not anomalies—they're a substantial fraction of the 2,435 studied. That's not a fringe case; that's a quiet revolution. It hints that the dominant mode of black hole growth in the universe may be a gentle, persistent drizzle rather than a monsoon. And if that's true, our entire narrative of galactic evolution needs a rewrite. As with all good science, this study raises more questions than it answers. How do these quiet black holes get their fuel? What regulates their growth without the shock and awe of mergers? And could our own Milky Way—a galaxy with a modest bulge—be a hybrid of both paths? The DESI data is just the beginning; future surveys will map these bulgeless galaxies in exquisite detail, watching them grow in real time. For now, we're left with a humbling reminder: even the most violent objects in the cosmos may be, at heart, creatures of habit. The source article, available at https://phys.org/news/2026-10-black-holes-quietly-galaxies-violent.html, captures this beautifully—a story of cosmic quietude that speaks louder than any collision.