Imagine listening to the heartbeat of the universe and discovering a rhythm that shouldn't exist. That's what happened to researchers analyzing gravitational waves: they heard the "bang" of collisions between intermediate black holes, cosmic objects that seemed to have come out of a theoretical physics textbook. These gravitational monsters, with masses between 100 and 300 times that of the Sun, represent the missing link between stellar black holes and supermassive ones. Their discovery rewrites what we know about the formation of the first cosmic giants.
Intermediate Black Holes: The Ghosts of the Cosmos Really Exist
For years, intermediate black holes have been the ghosts of cosmology. Theory predicted their existence, but no one had ever caught them in the act. The problem is simple: They are too massive to be born from the collapse of a single star, but too small to be the monsters that rule galaxies. It's a bit like looking for a mythical beast that lives in an evolutionary no-man's land.
The team led by Anjali Yelikar e Krystal Ruiz Rocha of Vanderbilt University he did what seemed impossible: has unearthed these elusive hidden giants reanalyzing data from the third LIGO and Virgo observation campaign. The result? Eleven gravitational events that tell the story of mergers between intermediate black holes, the heaviest ever recorded by gravitational astronomy.
Karan Jani, who heads the project, has a poetic but precise vision: “Black holes are the cosmic fossils par excellence. The masses we have detected in this analysis have remained highly speculative in astronomy for decades.”
When the Universe Sounds Different
The signals detected by LIGO and Virgo do not sound like the classic gravitational “chirp” we are used to hearing. As one researcher explained, “This doesn’t sound much like a chirp, which is what we typically detect. It’s more like something going ‘bang,’ and it’s the most massive signal that LIGO and Virgo have ever seen.”
The reason is physical: the more massive the black holes, the lower the frequency of the gravitational signal. These intermediate black holes produce waves that vibrate at frequencies so low that they are at the limit of the sensitivity of terrestrial instruments. But this very characteristic makes them precious: they allow us to peek into remote eras, when the universe was young and the first stars died, creating the first black holes.
The Missing Link in Cosmic History
The discovery of these intermediate black holes solves a puzzle that has plagued astrophysicists for decades. As I pointed out in this article, the universe appears to have a bimodal distribution of black holes: either they are small (up to 50 solar masses) or they are gigantic (millions of solar masses). But how do we get from one to the other?
The answer may lie in hierarchical mergers. These intermediate black holes may form when smaller black holes repeatedly collide, growing in mass with each collision. This is a process that requires dense environments, such as the centers of star clusters or the disks of gas surrounding supermassive black holes.
Intermediate Black Holes: A Window into the Distant Past
What makes these eleven events truly special is their ability to tell us ancient stories. The research, published on Astrophysical Journal Letters, opens a window into the first billion years of the universe, when the first massive stars ended their lives in spectacular explosions.
Jani He is convinced that we are living in a historic moment: “This is a population of black holes that offers us an unprecedented window into the very first stars that lit up our universe.”
Future observers, such as LISA which we have already discussed, could capture even older signals, allowing us to witness the birth of the first intermediate black holes. A journey through gravitational time that will take us to the origins of the universe as we know it.
The universe, it seems, still holds many secrets. And we are just beginning to hear its oldest stories.
