Limit to how big black holes can grow is astonishing

NASA/Goddard Space Flight Center

Limit to how big black holes can grow is astonishing

The supermassive black holes at the centers of galaxies are the most massive objects in the universe; the one in the middle of our Milky Way is as heavy as 4 million suns, and astronomers have spotted examples weighing in at billions of suns. But just how big can they grow? One astrophysicist says there is a limit: an eye-watering 50 billion suns. A black hole grows by feeding off an accretion disk of gas and dust that orbits around it (pictured). Friction in the disk causes material to drift inward until it succumbs to the black hole’s gravity and is swallowed up. This process heats up the gas to enormous temperatures so that it glows hot and very greedy black holes make the gas so bright it can be seen far across the universe as a quasar. But extremely massive black holes can cause instabilities in their accretion disks that make the gas and dust collapse into forming stars, which are better at evading the black hole’s gravity. As researchers report online this month in the Monthly Notices Letters of the Royal Astronomical Society, a black hole as large as 50 billion suns will likely cause its entire accretion disk to clump into stars and so have nothing more to feed on, halting its growth. There is some hope for these cosmic behemoths: They can still grow by swallowing up other supermassive black holes. 

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