Overview

• The team measured a 36.3 ± 6 billion-solar-mass black hole at the center of the Cosmic Horseshoe, marking the most precise direct mass estimate for an ultramassive dormant black hole to date.
• The study combined strong gravitational lensing of a background galaxy with stellar motion analysis within the lens galaxy to quantify a non-accreting black hole 5 billion light-years away.
• Observations revealed stars near the galaxy’s core orbiting at nearly 400 km/s under the black hole’s gravitational pull, providing independent confirmation of its mass.
• The host galaxy’s classification as a fossil group suggests the ultramassive black hole formed through successive mergers of smaller supermassive black holes when its parent galaxy group collapsed.
• The measured mass approaches theoretical upper limits for black hole growth and reinforces models of coevolution between host galaxies and their central black holes.