“Never look down to test the ground before taking your next step; only he who keeps his eye fixed on the far horizon will find the right road.” -Dag Hammarskjold
A black hole is a region of space that’s got so much mass in such a small volume that the escape velocity within a specific region is greater than the speed of light. We call this barrier from which light cannot escape the event horizon, and the sole arbiter of an event horizon’s size is the black hole’s mass. Since they come in a variety of sizes and a variety of distances from us, there’s a wide range of the apparent size of the event horizon as viewed from any location.
If you looked from Earth at the various black holes in space, which one would appear the biggest? Would it be the most massive ones, farther away, but large enough that their sizes dominate? Or would it be the closest ones, perhaps under 100 light years away, whose proximity to us makes all the difference? The answer is right in the middle: our galaxy’s supermassive black hole is the biggest, and we might be on the verge of imaging it directly!