Astronomer Helps Weigh Dormant Black Hole from 10 Billion Years Ago

An international team of astronomers has achieved a groundbreaking feat by directly measuring the mass of an inactive supermassive black hole from the early Universe, approximately 10 billion years ago. This accomplishment, led by Dr. Andrew Newman at Carnegie Observatories with significant contributions from Professor Meng Gu—formerly affiliated with The University of Hong Kong—pushes the limits of black hole research beyond our cosmic neighborhood.

Supermassive black holes are understood to reside at the centers of massive galaxies, influencing their surroundings through immense gravitational forces. Traditionally, black hole masses in nearby galaxies are inferred by analyzing the motions of stars within the sphere of influence—a region dominated by the black hole’s gravity. However, with increasing distance, resolving this sphere becomes challenging due to limited spatial resolution.

The breakthrough relied heavily on the James Webb Space Telescope (JWST) combined with a natural phenomenon known as gravitational lensing. A massive foreground galaxy cluster magnified the light from the distant galaxy MRG-M0138 by roughly 30 times, effectively acting as a cosmic telescope. This magnification allowed researchers to observe the stellar dynamics near the galaxy’s core in unprecedented detail, revealing the black hole’s presence through the gravitational impact on local star velocities rather than electromagnetic emissions, as the black hole is currently inactive.

The team found the black hole’s mass to be about six billion times that of the Sun, surprisingly large given the comparatively modest stellar bulge mass of its host galaxy. When compared to local galactic correlations, this black hole is approximately 12 times more massive than expected relative to the galaxy’s bulge. However, the velocity dispersion of stars—the range of their speeds influenced by gravitational potential—aligns well with typical black hole-galaxy relationships known today. This suggests that while the galaxy’s stellar mass was still assembling, possibly through later mergers, the central black hole and the gravitational environment in its vicinity were already mature.

These findings challenge prevailing assumptions that black holes and their host galaxies grow synchronously. Instead, this study presents compelling evidence that supermassive black holes can reach significant masses well ahead of the full assembly of their surrounding stellar populations. This has profound implications for understanding galaxy formation and the co-evolution of galaxies and black holes.

The ability to weigh inactive black holes at such high redshifts opens new avenues for characterizing the early Universe’s cosmic structures. By extending dynamical mass measurements out to redshift 2, astronomers can now test and refine models of galaxy and black hole growth with direct observational benchmarks.

Professor Gu emphasized the importance of combining JWST’s sensitivity with the magnifying power of gravitational lensing, stating that it unlocks the capability to examine distant galaxies in detail previously thought unattainable. This synergy heralds a new era in observational cosmology, allowing researchers to peer back into epochs when the Universe was still forming many of its fundamental components.

This study, published in Science, serves as a pivotal reference for future research seeking to unravel the timelines of black hole growth and galaxy evolution, marking a significant milestone in extragalactic astronomy.

Keywords

Supermassive black hole, JWST, gravitational lensing, early Universe, galaxy evolution, stellar dynamics, redshift 2, inactive black hole, galaxy bulge, velocity dispersion