Complex Numbers

Heavy Size

More proof that we're utterly obsessed with size:

    What is a black hole’s actual size?  
What do we mean by a black hole's size? A photon sphere? The minimal stable orbit? The event horizon? The singularity? Which one is right?

Out there in the Universe, size definitely matters.

Always lead with a subtle dick joke.

Objects that are stable, both microscopically and macroscopically, are described by measurable properties such as mass, volume, electric charge, and spin/angular momentum.

And, lately, political affiliation.

But “size” is a bit of a tricky one, particularly if your object is extremely small.

Snort.

After all, if all the mass and energy that goes into making a black hole inevitably collapses to a central singularity, then what does the concept of “size” even mean?

Obvious jokes aside, I've long wondered how you can measure the size of something that warps spacetime, which makes the concept of "size" very slippery (as if covered with K-Y)

The first thing you have to know about a black hole is this: in terms of its gravitational effects, especially at large distances away from it, a black hole is no different from any other mass.

I've mentioned something like this before, I know, but can't be arsed to find it right now. Black holes have some legitimately scary properties, but if they were going to eat entire galaxies, they'd have done it by now.

After all, we’re taught that black holes have an irresistible gravitational pull, and that they suck any matter that comes too close to their vicinity irrevocably into them. But the truth is that black holes don’t “suck” matter in anymore than any other mass.

I'm not well-versed in the math involved, but there's a region around a black hole within which orbits decay in a predictable way. Outside that region, black holes act like any other mass.

This is complicated by the prevalence of gas, dust, and debris in the vicinity, all of which would cause any orbit to eventually decay.

When a black hole rotates, it no longer has just one meaningful surface that’s a boundary between what can escape and what can’t; instead, there are a number of important boundaries that arise, and many of them can make a claim to being the size of a black hole, depending on what you’re trying to do. From the outside in, let’s go through them.

The rest of the article does just that; it's very interesting, and only a little bit math-oriented, but there's no need for me to comment on it. After all, I just wanted to make the point (pun intended) that even science writers are not above making the occasional dick joke.