London, UK – August 8, 2025
— Astronomers have made a groundbreaking discovery, announcing the finding of a black hole with a staggering mass of 36 billion suns, located approximately 5 billion light-years from Earth. This behemoth, which resides at the heart of one of the universe’s most massive known galaxies, the “Cosmic Horseshoe,” is among the largest black holes ever detected and challenges existing theories about how these cosmic objects grow. The finding, published in the journal Monthly Notices of the Royal Astronomical Society, was made possible through a novel and sophisticated method that combined the principles of gravitational lensing and stellar dynamics.
The immense size of this newly discovered black hole places it near the theoretical upper limit for such objects. While other ultramassive black holes have been identified, this one is particularly noteworthy because of the high degree of certainty in its mass measurement. Its host galaxy, the Cosmic Horseshoe, is so massive that it warps spacetime, bending and magnifying the light of a distant background galaxy into a striking horseshoe-shaped ring—a phenomenon known as gravitational lensing. Scientists used this effect to their advantage, as the black hole’s mass also contributes to this gravitational distortion.
What makes this discovery even more remarkable is that the black hole is “dormant,” meaning it is not actively consuming matter and therefore does not emit the high-energy radiation, such as X-rays, that astronomers typically use to locate black holes. Traditional methods of detecting and measuring black holes, which rely on observing the motion of nearby stars, are effective for closer galaxies but are rendered impossible at such vast distances. To overcome this, the research team developed a powerful new technique that combines two observational methods.
The first method involved analyzing the gravitational lensing effect. By meticulously studying how the light from the background galaxy was warped by the foreground galaxy, the astronomers could deduce the total mass of the Cosmic Horseshoe system. The second, and equally crucial, method involved observing the “stellar dynamics” of the host galaxy. The researchers were able to measure the extreme speeds at which stars were orbiting the galaxy’s core, nearly 400 kilometers per second. The immense gravitational pull required to make stars move at such velocities provided a clear and compelling signature of a central, ultra-massive object. By combining these two independent measurements, the team was able to confidently confirm the black hole’s presence and determine its mass with unprecedented precision.
The discovery of this ultramassive black hole in a fossil group galaxy—an end-state galaxy formed from the merger of two or more galaxies—sheds new light on the relationship between galaxies and their central black holes. According to the study, it is likely that the black holes from the merging galaxies also combined, creating the colossal object we see today. The research suggests that the size of both the black hole and its host galaxy are intimately linked, with the galaxy’s growth potentially funneling matter towards the central black hole.
This groundbreaking research is a testament to the power of combining different observational techniques to push the boundaries of what is possible in astronomy. The successful use of this new method opens up exciting possibilities for the future. Researchers hope to apply this same approach to data from space telescopes like the European Space Agency’s Euclid, with the goal of detecting more “hidden” ultramassive black holes across the universe. These future discoveries could provide critical insights into how black holes grow over cosmic time and their role in the evolution of galaxies. This latest finding not only expands our catalog of cosmic wonders but also deepens our understanding of the fundamental forces that have shaped the universe we inhabit.
