Astronomers have identified a black hole of staggering proportions, boasting a mass equivalent to 36 billion Suns, within the Cosmic Horseshoe galaxy. This discovery places it among the most massive black holes ever observed, pushing the boundaries of our understanding of these cosmic entities. The immense object is approximately 10,000 times more massive than the black hole at the center of our own Milky Way galaxy.
The Cosmic Horseshoe galaxy system, located about 5 billion light-years from Earth, acts as a gravitational lens. Its immense mass warps spacetime, bending the light from a more distant galaxy into a distinct horseshoe or ring shape, known as an Einstein ring. This gravitational lensing effect was crucial in detecting and measuring the mass of the black hole, particularly as it is a "dormant" black hole, not actively accreting material. Scientists confirmed the black hole's mass using stellar kinematics, analyzing the rapid motion of stars within the galaxy's core—approximately 400 kilometers per second—which indicates a supermassive object's gravitational influence. This method, enhanced by the gravitational lensing effect, allowed astronomers to probe deeper into the universe, providing a robust measurement with high confidence.
This discovery offers profound insights into the relationship between supermassive black holes and their host galaxies, suggesting that their growth is deeply interconnected. The Cosmic Horseshoe itself is considered a "fossil group," representing the culmination of multiple galaxy mergers. It is theorized that the black holes from these merged galaxies have coalesced to form the current ultramassive black hole. This finding provides a unique opportunity to study the end stages of both galaxy and black hole formation. The research detailing this discovery was published in August 2025 in the journal Monthly Notices of the Royal Astronomical Society.