What you can't see in this photo? Galaxy 4889’s massive black hole.

A long time ago in a galaxy far, far away...

A black hole had been "feasting" on its region's "cosmic cuisine" (NASA's words, not mine). This is what that insatiable black hole looks like.

Yes, that's just a black box. Because black holes are invisible, remember? (OK, I'll cut it out.)

This particular black hole — which is no longer dining on space matter and is instead resting comfortably in a food coma — is seriously enormous ... even by huge things in space standards.

This supermassive black hole in galaxy NGC 4889 is one of the largest NASA has ever discovered.

NASA originally spotted the black hole — which is a whopping 21 billion times the mass of our sun— in 2011.

The Hubble Space Telescope, however, just released an image of NGC 4889 hanging out roughly 300 million light-years away — the brightest dot in the center of the pic below. And even though you can't see the actual black hole within in (remember: invisible), the image is bringing a renewed interest in the galaxy's gargantuan gravitational center.

Photo by NASA & ESA.

To put this black hole's mass into perspective, the black hole at the center of the Milky Way (the galaxy we're spinning around in this very moment) has a mass about 4 million times our sun's. That's right — NGC 4889's black hole has a mass more than 5,000 times greater than our galaxy's black hole.

How do we know for sure how big it is if we can't see it? A very smart person who knows a lot about space noted on Hubble's website that astronomers can estimate the mass of black holes by measuring the velocity of stars moving around a galaxy's center — sort of like how you can't see the wind, but you can tell how hard it's blowing by seeing its effects on Donald Trump's hair.

Learning about this huge black hole made me realize two things: 1. I am terrified of black holes, and 2. I know very little about them.

So I decided to do some digging. And let me tell you — black holes are fascinating. Here are three facts that blew me away (or sucked me in?).

1. The tiniest black holes can be about the size of an atom ... but can have the mass of a f***ing mountain.

Black holes are like people — they come in all sizes.

An artist illustration of a quasar, or feeding black hole, eating up the space matter surrounding it. Image by NASA/ESAvia Getty Images.

There are three different kinds of black holes, mass-wise: primordial, stellar, and supermassive. The latter is the largest, with masses greater than 1 million of our suns. Evidence suggests they're at the center of every large galaxy.

Stellars (the Average Joes of black holes, if you will) are everywhere, relatively speaking — there could even be dozens floating around our very own Milky Way. These form after very big stars collapse, and they have masses up to 20 times greater than our sun.

Primordial black holes — the little guys of the group that formed in the early universe — can be as small as an atom but have the mass of a mountain. (Because science.)

2. Black holes are terrifying, but no — we shouldn't fear getting sucked into one.

Despite how bewilderingly scary the thought of one can be — their very definition hinges on the fact their gravity is so strong that not even light can escape — there are no black holes large enough to threaten Earth's existence anywhere nearby.

And as NASA points out, "black holes do not wander around the universe, randomly swallowing worlds." (Thank God.)

Bright flares are seen near Sagittarius A* — the black hole in the center of our own Milky Way galaxy — in 2003. Photo by NASA/CXC/MIT/F.K.Baganoff/Getty Images.

We should maybe focus on more reasonable threats facing our very existence as a species, like, say, climate change? (Just a thought.)

3. Black holes can collide. And we just learned that we can hear it happening — even a billion light-years away.

It turns out, Alert Einstein was right this whole time.

Photo by AFP/Getty Images.

Just this month, scientists from across the globe published a report that helps prove the last leg of Einstein's theory of relatively, which had to do with gravitational waves — "the ripples in the fabric of space-time," as The New York Times defined them (try wrapping your head around that).

Back in September 2015, scientists at the LIGO Scientific Collaboration detected a "chirp" using their antennas in Washington state and Louisiana. That chirp was the stretching and compressing of space — gravitational waves hitting Earth's surface.

So what do these waves have to do with black holes? Well, black holes created them.

Two stellar black holes had merged about a billion light-years away. This sent gravitational waves throughout the universe, distorting space-time as they rippled through. So, yes — two black holes that fused in one-fifth of an Earth second a billion years ago led to what could be "one of the major breakthroughs" in modern physics on Earth in 2016.

Do you feel like a black hole expert now?

OK, so maybe not an expert, but at least a little smarter when it comes to space stuff?

Black holes can be super-small and supermassive. They're completely horrifying by default but actually pose no real threat. And, as of just this month, they helped back up the most questionable aspect of Einstein's theory of relatively.

Bottom line: Black holes are a lot of things, starting with insanely cool.