The universe houses big, very big things. Really big. There are stars thousands of times larger than the Sun, capable of causing supernovae that shake space itself. But have you ever wondered what is the biggest, most massive object we’ve ever seen? I’m not talking about groups of objects like galaxies or nebulae, but the largest individual object in the universe that we have been able to observe. That object is called TON 618, and its features are so exaggerated that scientists find it hard to believe it exists. It is no longer just the object itself, but all the effects it causes around it.
TON 618 is an ultramassive black hole whose mass is equivalent to that of 66,000 million suns. It’s 18 billion light-years away, but the accretion disk spinning around it shines so brightly (as bright as a hundred trillion stars) that we can see it from Earth. There is a whole galaxy around it, but TON 618 is too bright to see. Therefore, we are looking at a version of TON 618 from 18,000 10,000 million years ago. And considering that we are talking about a black hole, today TON 618 may be much, much bigger than what we are seeing in our sky.
But even the measurements of TON 618 from the remote past are impressive. The radius of the black hole itself from its event horizon is 207 billion km. It is so large that we could fit eleven solar systems like ours, side by side, within it. Another way of trying to mentally encompass the disproportionate size of TON 618 is the one discussed in Kurzgesagt: a particle of light that was trapped in the event horizon would take a week to reach the infinitesimal singularity of the center.
All these data also allow us to know that TON 618 formed when the universe was very young, “only” 3.4 billion years after the Big Bang. Since then it has been absorbing matter, trapping it in its gravitational field, and it won’t stop doing so until there is literally nothing left to absorb.