A team scientific international, in which are found researchers from the Institute of Astrophysics of the Canary Islands (IAC) and the Gran Telescopio de Canarias, has found a drastic change in a supermassive black hole. The cosmic giant is 10 billion light-years away, the object dimmed until reaching approximately one-twentieth of its previous brightness in just two decades, an interval "extraordinarily short on a cosmic scale", as experts have informed.
The discovery was made within the framework of a collaborative observation project that integrates the Subaru telescope of Japan and the GTC of the Roque de los Muchachos Observatory, in La Palma, along with contributions from other observatories worldwide. By combining wide-field sky surveys with detailed follow-up observations, the team was able to reconstruct how the activity of this distant black hole evolved over time.
When a cosmic giant runs out of fuel
At the center of many galaxies supermassive black holes are found with a mass millions or even billions of times greater than that of the Sun. When large quantities of gas fall towards them, the material forms a hot rotating disk that shines intensely throughout the Universe. These luminous regions are known as active galactic nuclei.
For decades, it was believed that these active phases lasted hundreds of thousands or even millions of years, a period too long for significant changes to be observed over a human lifetime. The new observations question that view. “It's as if a powerful cosmic engine suddenly started running out of fuel,” explains Tomoki Morokuma, researcher at the Instituto Tecnológico de Chiba (Japan) who has led the study. “We are seeing solid evidence that the gas flow feeding the black hole decreased very rapidly,” he adds.
It is not simply a game of lights
Active black holes usually present small fluctuations in their brightness, and some systems dominated by powerful jets can vary drastically in short periods. However, the new observations reveal a fundamentally different phenomenon.
Using data ranging from optical and infrared light to radio and X-ray observations, the team discovered that the dimming cannot be explained by dust temporarily blocking the view nor by changes in the emission of the jets. Instead, evidence indicates that the accretion disk itself, the structure in which gas spirals inward before falling into the black hole, significantly weakened.
The team estimates that the speed at which matter flowed into the black hole could have decreased by up to fifty times in just a few years in the object's own reference frame. Such a rapid intrinsic change suggests a significant disruption in the gas supply reaching the center of the galaxy.
A worldwide collaboration
To detect this exceptional phenomenon it was necessary to compare observations separated by decades. The wide-field images obtained with the Subaru telescope allowed the team to identify this unusual object for the first time by contrasting recent data with previous observations, among them those from the Sloan Digital Sky Survey.
Follow-up observations made with the GTC, the world's largest optical and infrared telescope, provided crucial measurements needed to understand how the black hole's environment was evolving. “The data from the GTC's infrared observations were fundamental in demonstrating that the entire central engine was fading, not just a part,” states Nieves Castro Rodríguez, GTC astronomer and co-author of the article.
With the complementary technical capabilities of several observatories, the team reconstructed the long-term history of the system and ruled out other possible explanations. “This discovery demonstrates that only through international cooperation among observatories can we capture exceptional cosmic phenomena that would otherwise go completely unnoticed,” states Josefa Becerra González, IAC researcher and co-author of the article.
Observing how black holes change in real time
In recent years, it has begun to be discovered that some active black holes can undergo surprisingly rapid transformations. Previous studies have revealed drastic changes in nearby active galaxies, suggesting that the growth of supermassive black holes could be much more dynamic than previously believed.
“We used to think that supermassive black holes only changed over extremely long timescales,” states José Acosta Pulido, an IAC researcher and co-author of the article. “But this discovery, along with some previous findings about the very few active galactic nuclei that change their appearance, suggests that some of them can alternate between active and quiet states in just a few years,” he highlights.
A new era of discoveries
Wide-field observations, which capture vast areas of the sky at once, have become a fundamental approach in modern optical astronomy. This study demonstrates how combining data from different epochs and wavelengths can reveal long-term changes in galactic nuclei that would otherwise remain hidden.
With instruments like the Hyper Suprime-Cam of Subaru and future high-sensitivity surveys like the Vera C. Rubin Observatory (LSST), Euclid and the Nancy Grace Roman Space Telescope of NASA, many more active galactic nuclei are expected to be discovered in low-activity or even “quiescent” states. Statistical studies of such objects will help reveal the physical conditions under which the gas supply stops or resumes to supermassive black holes, offering a new perspective on how these cosmic giants grow and influence their host galaxies.
At the same time, the development of new theoretical models capable of explaining the rapid changes observed in this study remains a significant challenge for astrophysicists. Toshihiro Kawaguchi, from the University of Toyama, who contributed mainly to the theoretical interpretation, explains: “This object shows changes too rapid to be explained by standard models, and will serve as a reference when developing new theoretical frameworks. We will investigate what physical conditions can reproduce the observed data.”
Every new discovery brings scientists closer to answering one of the fundamental questions of modern astronomy: how the largest black holes in the Universe grow and how they stop.
