They’re cosmic icons and sci-fi legends—and nearly 50 years after becoming scientific headliners, black holes are still full of surprises. In fact, one of the most massive ever found may have just been discovered by chance. And we’re not talking ordinary supermassive—we’re talking ultramassive.
Gravitational lensing is the phenomenon behind it all. When huge amounts of matter bend space and time, they also bend light—acting like a giant magnifying glass for whatever’s behind them. This idea first surfaced in 1924 (yes, really), but it wasn’t until Einstein picked it up in 1936 that it got any attention. He didn’t think we’d ever observe it. Turns out, he was wrong—and lucky for us, because we now use it to study dark matter, spot distant galaxies, and zoom in on cosmic objects billions of light-years away.
The first real observation? That came in 1979, with the famous Twin Quasar in Ursa Major. It proved that gravitational lensing wasn’t just theory—it was part of the cosmic toolkit.
In a vacuum, light usually travels in a straight line. But in a space distorted by a massive celestial body, such as a galaxy, this trajectory is deflected! Thus, a light source located behind a galaxy has an apparent position different from its actual position: this is the phenomenon of gravitational mirage. This video is from the web documentary “The Odyssey of Light” and was integrated into the web documentary “Embark with Dark Matter”. © CEA, Animea
A cosmic horseshoe hides a sleeping giant
Among the best-known lensing events is the “Cosmic Horseshoe,” created by the galaxy LRG 3-757. Located in the Leo constellation, about 5 billion light-years from us, this massive elliptical galaxy warps light into a near-perfect ring, called an Einstein ring.
But there’s more to this galaxy than meets the eye. According to a new study published in the Monthly Notices of the Royal Astronomical Society, it might house a hidden heavyweight—one of the biggest black holes ever discovered. Astronomers now believe it could have a mass of 36 billion solar masses, rivaling the previous record holder, Holm 15A*.
Some researchers refer to any black hole above 5 billion solar masses as “ultramassive,” though the term isn’t universal. What is certain is that black holes this big are still deeply mysterious—especially since most of what we know comes from smaller ones, like the 4-million-solar-mass black hole at the center of our own galaxy.
As for how massive a black hole can actually get? The jury’s still out. Some theories cap it at 50 billion; others go as high as 250 billion. Either way, we’re still far from knowing the full story.
Another image of the Cosmic Horseshoe, but with both images of a second background source highlighted. The faint central image forms near the black hole, which made this new discovery possible. © NASA, ESA, Tian Li (University of Portsmouth)
Mass confirmed by star motion—not light
To calculate the size of this cosmic beast, astronomers didn’t rely on its glow—it’s not active. Instead, they tracked the movement of nearby stars traveling at incredible speeds (nearly 400 km/s). These orbits are shaped entirely by gravity, giving scientists a direct way to weigh what’s at the center.
“This black hole is one of the top ten most massive we’ve ever found—possibly the most massive,” said Professor Thomas Collett of the University of Portsmouth. “Most black hole measurements are full of uncertainty. But this method gives us something much more precise.”
His co-author, Carlos Melo from Brazil’s UFRGS, added: “This one isn’t even feeding—it’s a dormant black hole. We only saw it because of how strongly it pulls on the stars around it.”
The truly exciting part? This method works even when black holes are completely invisible. And it could revolutionize how we find and measure them across the universe. Instead of relying on guesswork from active systems, this technique—based on a mix of lensing and stellar dynamics—gives us a clear, direct picture.
The Royal Astronomical Society sees major potential: “This discovery is key to understanding how supermassive black holes shape their galaxies. With the success of this method, we’re now looking to ESA’s Euclid telescope to uncover even more—and unravel how these giants help stop galaxies from forming new stars.”
Laurent Sacco
Journalist
Born in Vichy in 1969, I grew up during the Apollo era, inspired by space exploration, nuclear energy, and major scientific discoveries. Early on, I developed a passion for quantum physics, relativity, and epistemology, influenced by thinkers like Russell, Popper, and Teilhard de Chardin, as well as scientists such as Paul Davies and Haroun Tazieff.
I studied particle physics at Blaise-Pascal University in Clermont-Ferrand, with a parallel interest in geosciences and paleontology, where I later worked on fossil reconstructions. Curious and multidisciplinary, I joined Futura to write about quantum theory, black holes, cosmology, and astrophysics, while continuing to explore topics like exobiology, volcanology, mathematics, and energy issues.
I’ve interviewed renowned scientists such as Françoise Combes, Abhay Ashtekar, and Aurélien Barrau, and completed advanced courses in astrophysics at the Paris and Côte d’Azur Observatories. Since 2024, I’ve served on the scientific committee of the Cosmos prize. I also remain deeply connected to the Russian and Ukrainian scientific traditions, which shaped my early academic learning.
