Astronomers have identified an ultramassive black hole weighing roughly 36 billion times the mass of the Sun in the Cosmic Horseshoe galaxy, about 5 billion light-years from Earth. The object is one of the ten largest black holes ever measured and may be the heaviest confirmed to date, edging close to theoretical upper limits on black-hole mass. A team led by Thomas Collett at the University of Portsmouth combined stellar-kinematics data with gravitational-lensing analysis of the galaxy’s distinctive Einstein Ring. By tracking how stars orbit near the galactic centre and how the galaxy’s immense gravity bends light from a more distant background source, the researchers were able to constrain the black hole’s mass far more tightly than with either method alone. The finding, detailed in the 7 August issue of Monthly Notices of the Royal Astronomical Society, strengthens the observed correlation between the mass of a galaxy and that of its central black hole. It also challenges current models of black-hole growth, which struggle to explain how such a colossal object could form without quickly exhausting its surrounding fuel or disrupting its host galaxy. Follow-up observations with ESA’s Euclid space telescope and other instruments are expected to reveal whether similar giants are more common than previously thought.