A distant galaxy fades 20-fold in two decades, challenging models of supermassive black hole evolution

An international team has documented one of the most extreme phenomena ever recorded in active galactic nuclei: a galaxy located some 10 billion light-years away dropped to one-twentieth of its original brightness in just 20 years. The finding, published in the Publications of the Astronomical Society of Japan, challenges current understanding of how supermassive black holes evolve.

What is an AGN

Most large galaxies harbor a supermassive black hole at their center, with masses hundreds of millions of times that of the Sun. When surrounding gas falls inward under the black hole’s gravity, it forms a rotating structure known as an accretion disk. Friction within the disk heats the material to extreme temperatures, releasing enormous amounts of energy. The result is an extraordinarily luminous central region called an active galactic nucleus, or AGN. If the flow of gas into the accretion disk weakens, the emission drops and the galactic center dims.

The most dramatic shutdown on record

The team, led by the Chiba Institute of Technology (Japan) and including researchers from the University of Potsdam, the University of Toyama, the Instituto de Astrofísica de Canarias, the National Astronomical Observatory of Japan, and Ritsumeikan University, compared images from the Sloan Digital Sky Survey with recent observations from the Subaru Telescope using its Hyper Suprime-Cam instrument.

The data showed that the apparent brightness of galaxy J0218−0036 —at a redshift of 1.8, corresponding to roughly 10 billion light-years away— fell to approximately one-twentieth of its original level over about 20 years. AGN typically vary in brightness by around 30%, making a decline of this magnitude extraordinarily rare. The team immediately followed up with the Gran Telescopio Canarias and conducted optical, near-infrared, and radio observations, also analyzing archival X-ray and infrared data alongside photographic plates taken about 70 years ago.

Running out of fuel

By comparing the observed changes in optical and infrared brightness with theoretical models, researchers estimated that the mass accretion rate —the rate at which gas flows into the black hole— dropped to roughly one-fiftieth of its previous level in about seven years. This suggests that the supply of material feeding the black hole may be rapidly shutting down.

The possibility that a dust cloud temporarily blocked the light from the accretion disk was ruled out, as it cannot account for the observed changes across the wide range of wavelengths from optical to infrared. The results indicate that the physical state of the accretion disk itself changed dramatically. What mechanism could cause such a rapid change remains unclear, and further observations and theoretical studies will be required.

Models that need rethinking

This discovery shows that supermassive black hole activity in galactic centers can change dramatically on timescales of just a few years to a few decades —short enough to be observed within a human lifetime. Until now, mass accretion onto supermassive black holes in AGN was generally thought to vary slowly over tens of thousands of years or longer. The new result directly challenges that view.

Tomoki Morokuma, Principal Staff Scientist at the Chiba Institute of Technology’s Astronomy Research Center and lead author of the study, noted that it is fascinating that an active galactic nucleus can change its brightness so dramatically over such a short period of time, and that this fading appears to be driven by a large change in the accretion rate. Co-author Toshihiro Kawaguchi of the University of Toyama added that the object displays rapid variability that cannot be explained by standard models, and that it represents an important test case for developing new theoretical frameworks.

Wide-field surveys as a key tool

Wide-field surveys, which efficiently observe large numbers of objects across broad areas of the sky, have become a major trend in modern astronomy. This study demonstrates that combining data from different wavelengths and different epochs can reveal long-term changes in supermassive black hole activity. If more fading or dormant AGN are discovered through future wide-field imaging surveys, they could provide important clues to understanding how galaxies and their central black holes co-evolve over cosmic time.

Source: Subaru Telescope – Phys.org, March 25, 2026. Original publication: Tomoki Morokuma et al., A possible shutting-down event of mass accretion in an active galactic nucleus at z ~ 1.8, Publications of the Astronomical Society of Japan (2025). DOI: 10.1093/pasj/psaf115

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