<\/p>\n Scientists have long wondered why this could be: Are there just fewer feeding black holes out there now, or is some external force stunting their growth?<\/p>\n You may like<\/p>\n The actual reason may be that there’s simply less material for them to munch on, scientists suggested in a paper published Dec. 17 in The Astrophysical Journal<\/a>.<\/p>\n “We knew black holes were growing more slowly, but not why \u2014 and it turned out to be that individual black holes are consuming material much less rapidly, rather than there simply being fewer growing black holes or smaller ones,” study co-author Fan Zou<\/a>, an astronomer at the University of Michigan, told Live Science via email.<\/p>\n Beefy black holes on a diet<\/p>\n Studying the growth of black holes is crucial for understanding galactic evolution and star birth, because SMBHs and their host galaxies evolve in a coordinated manner. SMBH sizes also correlate with the total mass of stars and their chaotic movements in a galaxy’s bulge \u2014 the football-shaped central region<\/a> where stars are densely packed.<\/p>\n To measure how black hole growth has changed throughout cosmic time, the researchers utilized data from nine extragalactic surveys collected in a “wedding cake” design. These tiered layers include shallow surveys of large, relatively nearby regions of the sky, as well as extremely deep “pencil-beam” looks at smaller fields, gathered from the world’s premier X-ray-based space telescopes, including NASA<\/a>‘s Chandra X-ray Observatory, the European Space Agency<\/a>‘s XMM-Newton and the German-Russian eROSITA.<\/p>\n “X-ray light is arguably the best tracer of black hole growth,” lead author Zhibo Yu<\/a>, an astronomer at Penn State, told Live Science via email. “It is ubiquitously produced by growing supermassive black holes and has high contrast compared to the background star light. It also has high-penetrating power \u2014 that’s why it’s commonly used in medical imaging \u2014 so that it is less affected by the obscuring gas and dust in the galaxy.”<\/p>\n Altogether, the researchers analyzed multiwavelength observations<\/a> of 1.3 million galaxies and 8,000 actively feeding, X-ray-spewing SMBHs to determine why the black holes’ growth rate has plummeted.<\/p>\n Have black holes had their heyday?<\/p>\n The research tested three main ideas. For example, are the black holes in the modern universe gobbling less matter? Alternatively, are they simply smaller and, therefore, less gravitationally gluttonous than their ancient predecessors? Or are there fewer actively growing black holes overall?<\/p>\n What to read next<\/p>\n The researchers concluded that the black holes’ consumption has slackened as the amount of cold gas for them to gobble has decreased since cosmic noon, approximately 10 billion years ago. “What surprised me most was that we could actually isolate the main reason, and there is indeed a dominating reason instead of a messy mix,” Zou explained.<\/p>\n \n Scenarios highlighting the hypotheses for decreasing black hole growth rates over cosmic time. (Image credit: Penn State\/Z. Yu)<\/p>\n This decrease in growth rates appears to be significant. “Our best estimate is that the decrease is a factor of 22,” study co-author Neil Brandt<\/a>, an astrophysicist at Penn State, told Live Science via email. Although this study did not address the bafflingly fast black hole growth<\/a> in the very early universe, “it does the best job so far of [addressing] the final 75% of cosmic time \u2014 a large majority!”<\/p>\n Future work may focus on additional datasets, such as wide-field X-ray surveys from Chandra and XMM-Newton, as well as multiwavelength data from other observatories. As a result, astronomers will be able to uncover larger SMBH populations, including even older examples and those that are obscured by dense dust and gas.<\/p>\n Finally, the research further confirms that the eras of rampant SMBHs are behind us. “We do not expect many SMBHs to emerge and significantly grow in the future,” Zou said. “Actually, we found in 2024 that the number of SMBHs was almost settled by 7 billion years ago \u2014 and will likely continue to be so in the future.”<\/p>\n \u55bb Z. \u77e5. Y., Brandt, W. N., Zou, F., Luo, B., Ni, Q., Schneider, D. P., & Vito, F. (2025). The Drivers of the Decline in Supermassive Black Hole Growth at z < 2. The Astrophysical Journal, 995(2), 205. https:\/\/doi.org\/10.3847\/1538-4357\/ae173d<\/a><\/p>\n![\"A](\"https:\/\/www.newsbeep.com\/il\/wp-content\/uploads\/2026\/04\/zbpF4MGGPXi264i2tHUZma.jpg\")
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