Using NASA's James Webb Space Telescope, an international team of astronomers has detected and "weighed" the most distant dormant black hole ever found—a cosmic object so far away that its light left its home galaxy when the universe was only 3 billion years old, about a quarter of its current age.
The black hole sits at the heart of galaxy MRG-M0138, located more than 10 billion light-years away, and tips the scales at roughly 6 billion times the sun's mass. This discovery pushes the boundaries of what was previously thought possible: the previous record for a dormant black hole detected this way stood at only 700 million light-years away—making this find 15 times farther than anything astronomers had weighed before using this technique. The work, published in Science and led by Dr. Andrew Newman of Carnegie Science in Pasadena, California, represents the first time stellar dynamics—a method long used to measure black holes in nearby galaxies—has successfully reached back into the early universe.
Dormant black holes present a unique challenge to astronomers. Unlike their active cousins, which pull in gaseous material that shines brilliantly across the cosmos, dormant black holes emit no light whatsoever. Their presence can only be detected by watching how nearby stars move around them. The team tracked these stellar motions using JWST's spectroscopic capabilities, observing how quickly stars orbit and how their speeds vary depending on their distance from the black hole's center. These variations reveal the gravitational pull of the invisible giant.
But measuring such faint stellar movements at a distance of 10 billion light-years should have been impossible. The team overcame this seemingly insurmountable obstacle through a stroke of cosmic luck: gravitational lensing. Another galaxy positioned directly between MRG-M0138 and Earth bent and magnified the light from the distant galaxy like a natural cosmic magnifying glass, enlarging it by a factor of 30. This magnification allowed researchers to reconstruct the internal details of the galaxy with far higher resolution than conventional observation would permit, revealing the telltale motions of stars whirling around their invisible master.
"By combining JWST data with gravitational lensing, we could peer inside the black hole's sphere of influence, where its gravity boosts the speeds of stars," Dr. Newman explained. "This is one of the best techniques we have to weigh a black hole, so we were excited to extend it to a much earlier period in cosmic history."
Professor Richard Ellis of UCL Physics & Astronomy, a senior author on the study, emphasized the implications of this breakthrough. "Determining how stars collectively move within the core of this distant galaxy has allowed us to measure the mass of its otherwise undetectable supermassive black hole. By demonstrating the feasibility of such a technique for galaxies in the early universe, we can now undertake a more complete census of how black holes develop over time and infer their role in shaping galaxy evolution."
The discovery raises profound questions about how supermassive black holes formed in the early universe. Finding such a massive black hole so far back in time challenges existing models of black hole growth and galaxy evolution. As JWST continues its observations, astronomers now have a proven method to explore this population further, potentially unlocking secrets about some of the universe's most mysterious objects.