Black Holes, so hot right now.

So, black holes. Equal parts awesome, terrifying and confusing. How big are they, really?
There exist several commonly utilized methods for conveying their size astronomically, one of which is expressing their magnitude in terms of solar masses (M☉) . "Solar mass" is simply the mass of Sol, our sun.
Another is measuring their radius, or in terms of black holes, their Schwarzschild radius. This is simply measuring from the center of said celestial object outward, insofar that it reaches the event horizon.

So if you've ever googled something along the lines of "gigantic black hole" then you've probably seen this image. NGC 1277, when discovered in 2012, was originally thought to be so large that it contradicted modern galaxy formation and evolutionary theories.
It is indeed gigantic - if you haven't been able to wrap your head around the picture, the tiny dot in the middle is Earth's orbit - that is, the path it takes around the sun which has a diameter of approximately 17 light-minutes. Light-minutes, in that it takes light about 17 minutes to cross this distance moving at 299,792,458 meters per second.
The blue circle is Neptune's orbit - It takes light 8.3 HOURS to cross from one side of the blue circle to the other. Try to keep in mind, Neptune is 2.795 BILLION miles away from our sun.
So, while it's difficult to put meaning to these numbers even with the picture, it's basically showing you that NGC 1277 is just stupid big. 5 billion solar masses big, big.

While NGC 1277 held the title for a bit, it didn't take long for us to find another one that was bigger. Pictured far left is NGC 1277, the same black hole pictured above in #2. Next to it is Holmberg 15A - doubling the size of it's predecessor as largest known black hole.
Another recent post cited Holmberg 15A as being the largest known in the universe, but we're just getting started. It is huge, but we found another one bigger yet.
This is where shit starts getting crazy - OJ 287 is believed to be a set of binary supermassive black holes, or two supermassive black holes in close orbit with a combined mass of 18 billion solar masses.

The GIF above illustrates how these two giants will eventually merge to become a single supermassive black hole in about 10,000 years. Apparently, the smaller supermassive black hole of the two, consisting of "only" 100 million solar masses, punches through the accretion disk of the larger one about once every 12 years. If you're not sure what an accretion disk is, check out the stylized representation in picture #1
THEN imagine a supermassive black hole 100 million times the mass of the sun just tearing through it. How badass would that be to see.

(Video credit to LIGO Lab Caltech : MIT, https://youtu.be/I_88S8DWbcU)

So then comes along S5 0014+81, and this is about the point where astronomers just start throwing around terms like "ultra-massive black hole", because what else can you really do? Whereas OJ 287 above is estimated to have a mass of 18 billion solar masses, S5 0014+81 is thought to clock in around 40 Billion solar masses, more than twice that of the aforementioned.
Not only is this thing just staggeringly massive, is also happens to be a "distant, compact, hyperluminous, broad-absorption line quasar (quasi-stellar object) " or otherwise known as a blazar. I honestly don't even know what they're talking about at this point, but they sound serious.

Blazars are said to be some of the most energetic and violent phenomena in the universe, ejecting jets of plasma at up to 99% the speed of light tens of thousands of light years into space. They are also some of the most luminous objects within the universe, initially thought perhaps to be galaxies themselves. Wild.

(Video credit to Space.com, https://youtu.be/sk7HTRlb4XY)

So, where does it end? That's actually a really awesome question, and I think by now we should know that we really just don't know. Now what we DO know is that as of this month an even larger black hole was found, making that last blazar look pretty weak.
Enter TON 618: a very distant and extremely luminous quasar—technically, a hyperluminous, broad-absorption line, radio-loud quasar. Similar to all those words I don't really understand above, plus, it's rare in that it has extremely strong radio emissions. So how big is this thing? Current estimates are placing it at 66 billion solar masses (!?!), completely redefining "supermassive". The surrounding galaxy is not visible from Earth, because the quasar itself outshines it. With an absolute magnitude of −30.7, it shines with a luminosity of 4×10^40 watts, or as brilliantly as 140 trillion Suns.

And so that should just about bring us up to speed. If you made it this far, thanks for reading. There's a bunch of really cool space stuff happening right now and it's amazing to see people again excited to push the boundaries of human knowledge and understanding. If you were not already aware, the James Webb Space Telescope (https://www.jwst.nasa.gov/) is set to replace the Hubble telescope next year, and give us an absolutely unparalleled view into the cosmos. Truly exciting times indeed.

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References
https://www.forbes.com/sites/quora/2017/06/08/the-physics-of-black-holes-explained-for-non-scientists
http://hubblesite.org/reference_desk/faq/answer.php.id=62&cat=exotic
https://en.wikipedia.org/wiki/List_of_most_massive_black_holeshttps://www.revolvy.com/main/index.php?s=TON%20618
http://ned.ipac.caltech.edu/https://www.revolvy.com/main/index.php?s=TON%20618
https://www.noao.edu/education/peppercorn/pcmain.html

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Edit: Thanks for checking this out! I will do a follow up post with some cool stuff.
As of writing, there have been 17 "your Mom" jokes and 6 Muse references made. Although I think saying this will likely have the opposite of the desired effect, it had to be said. Stay inspired, Imgur.