Thursday, May 12, 2022

TON 618, possibly the largest object in the entire known universe

The universe houses big, very big things. Very good. There are stars thousands of times larger than the Sun, capable of causing supernovas that shake up space itself. But have you ever wondered what is the biggest and most massive object we've ever seen? I'm not talking about groups of objects like galaxies or nebulae, but the largest single object in the universe that we've been able to observe. 

This object is called TON 618, and its features are so exaggerated that scientists have a hard time believing its existence. It is no longer just the object itself, but all the effects it causes around it. A black hole larger than ten solar systems placed side by side TON 618 is an ultramassive black hole whose mass is equivalent to 66 billion sols. It is 18 billion light-years away, but the accretion disk that revolves around it shines so brightly (as bright as a hundred trillion stars) that we can see it from Earth. 

There's an entire galaxy around you, but the glow of TON 618 is too big to see. So we're looking at a version of TON 618 from 18 billion years ago. And considering we're talking about a black hole, today TON 618 could be much, much bigger than what we're seeing in our sky. But even the measurements of TON 618 from the distant past are impressive. The proper black hole radius from its event horizon is 207 billion kilometers. It's so big that we could put eleven solar systems like ours, side by side, inside it. 

Another way to mentally try to understand the disproportionate size of TON 618 is the one discussed in Kurzgesagt: a particle of light that was trapped at the event horizon would take a week to reach the infinitesimal singularity at the center. All this data also lets us know that TON 618 was formed when the universe was very young, “only” 3.4 billion years after the Big Bang. Since then, it has been absorbing matter that traps it in its gravitational field, and it will not stop until there is literally nothing left to absorb.

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