Back in November, a ripple passed through Earth. Not the kind you’d feel with your feet on the ground, but one that shuddered across space-time itself—a literal echo of two massive black holes smashing into each other somewhere near the edge of the Milky Way.

The signal, now confirmed by the LIGO-Virgo-KAGRA (LVK) Collaboration, marks the most significant black hole merger ever detected. And the cosmic corpse it left behind? A black hole roughly 225 times the mass of our sun. That’s not big—that’s freakishly huge.

Previously, the record holder was a 142-solar-mass black hole. But what’s even more bizarre is where these colliding black holes came from. Each one fell into what physicists call a “mass gap”—a range (roughly 60 to 130 solar masses) where stars shouldn’t be able to collapse into black holes. 

“We don’t expect black holes to form between about 60 and 130 times the mass of the sun,” said physicist Mark Hannam of Cardiff University, part of the LVK team, in an interview with Live Science. “But in this observation, the black holes appear to lie in that mass range.”

That’s a problem. Or, depending on how you look at it, a really exciting clue.

Two Massive Black Holes Merged Into One 225 Times the Mass of the Sun

Black holes usually form when massive stars die. But when stars get too massive, theory says they should explode and scatter themselves instead of collapsing. That makes this detection—named GW231123—an astronomical curveball. The black holes were also spinning fast, which makes analyzing their signal harder. “Our different models give different results,” Hannam said. “Although we’re sure the black holes are very massive, we don’t measure the masses especially accurately.”

Scientists know something enormous collided, but calculating the exact masses is tricky. The models used to measure black holes don’t handle fast-spinning ones well, and these two were spinning like tops in a blender. Since different simulations yielded different results, it means the numbers are still somewhat uncertain.

Despite the uncertainty, the signal is strong enough to suggest we’re looking at one of the best candidates yet for an intermediate-mass black hole—a kind of theoretical middle child between regular-sized black holes and the monstrous ones at the centers of galaxies. Until now, evidence for these has been rare and mostly circumstantial.

LIGO and its partner detectors have detected hundreds of black hole mergers since 2015, but this one may ultimately rewrite what we thought we knew about how the universe forms its most violent objects.