The largest things in theĀ
universe are black holes.Ā Ā In contrast to things like planets orĀ
stars they have no physical size limit,Ā Ā and can literally grow endlessly. Although inĀ
reality specific things need to happen to createĀ Ā different kinds of black holes, from really tinyĀ
ones to the largest single things in the universe.Ā Ā So how do black holes grow and howĀ
large is the largest of them all? This video will not discuss how black holes workĀ
or how they form since weāve looked at that inĀ Ā detail in our black hole and neutron star series,Ā
you can check them out afterwards. For now we areĀ Ā interested in finding the largest thing in theĀ
universe. Let us start really, really small. Primordial Black holes The smallest kind of black holes may or may notĀ
exist. If they do, they are probably the oldestĀ Ā objects in the universe, older even than atoms.Ā
They would have formed just after the big bang,Ā Ā when the universe was so dense withĀ
violent energy, that any tiny pocketĀ Ā that was just slightly more dense thanĀ
its neighbors could produce a black hole. The smallest Primordial Black Hole thatĀ
could still be around would be a trillionĀ Ā kilograms or so, the mass of a big mountain.Ā
And yet they would be no bigger than a proton.Ā Ā A Primordial Black hole with the mass ofĀ
earth would barely be larger than a coin.Ā Ā This makes them very hard to find, so weĀ
havenāt actually observed any yet ā ifĀ Ā they exist they may even be the mysteriousĀ
dark matter that holds galaxies together. Letās move on to the kinds of black holesĀ
that we know for sure ARE out there. Stellar Black Holes To make a black hole we need to compress enoughĀ
matter so that it collapses into itself. AfterĀ Ā that, the more mass we throw at it, theĀ
larger it becomes. In today's universe,Ā Ā only the most violent cosmic events can createĀ
the necessary conditions, such as the merger ofĀ Ā neutron stars or when the core of a very massiveĀ
star collapses in a supernova. To have a unit toĀ Ā work with here, weāll use the mass of our sun,Ā
about 2 million trillion trillion kilograms. The smallest known black holeĀ
has 2.7 times the mass of the sunĀ Ā which works out as a sphere around 16 kmĀ
in diameter, large enough to cover Paris. Another lightweight black hole is theĀ
companion to the V723 Mon red giant star.Ā Ā This star is 24 times larger than our sun,Ā
30 million kilometer in diameter. And yet,Ā Ā it is thrown around by a tiny black holeĀ
just 17.2 km wide. This tiny thing bullyingĀ Ā the star is so much smaller that we canĀ
barely even show them in comparison. One of the largest known stellar black holes isĀ
M33 X-7. It currently spends its time eating a 70Ā Ā solar mass blue giant, bit by bit. As all thatĀ
stolen matter circles towards the black hole,Ā Ā like water going down a drain, friction heatsĀ
it up to temperatures high enough to shineĀ Ā 500,000 times brighter than our Sun! AndĀ
yet, X-7 is āonlyā 15.65 solar massesĀ Ā and 92 km wide, just big enoughĀ
to cast a shadow on Corsica. To grow much larger, black holes have to eitherĀ
devour a lot of stars or better, merge with oneĀ Ā another. The instruments that make it possibleĀ
to detect these mergers are very new so we areĀ Ā currently discovering a lot of exciting things.Ā
Like two massive black holes that we detected inĀ Ā a galaxy 17 billion lightyears away. As they spunĀ
around each other violently, they released moreĀ Ā energy in the form of gravitational waves than theĀ
combined light from all the stars in the milky wayĀ Ā in 4400 years. The new black hole they formed isĀ
about the size of Germany and is 142 solar masses. And here we hit a curious gap in scale. There are lots of black holes up to 150 solarĀ
masses. And then there is nothing for a longĀ Ā time. Until we suddenly hit black holes,Ā
that are millions of times more massive. Which is a bit confusing, because we had thisĀ
idea that black holes are consistently growingĀ Ā and growing. But for the most massive black holesĀ
this process is not fast enough to explain theirĀ Ā existence today. The universe is simply notĀ
old enough for these supermassive black holesĀ Ā to have formed by eating stars and merging withĀ
each other. Something else must have happened. To explain how we got the largest blackĀ
holes in the universe, we might need theĀ Ā largest stars that ever existed: Quasi Stars.Ā
To get a sense of scale, we can compare themĀ Ā to the largest stars that exist today. OurĀ
Sun is like a grain of sand next to them. We donāt know if Quasi Stars actually existed butĀ
they are an interesting concept when it comes toĀ Ā supercharging black hole development. The idea isĀ
that the matter in the early universe was so denseĀ Ā that quasi stars could grow to thousands ofĀ
times the mass of our sun. The cores of theseĀ Ā stars might have been crushed by their own weightĀ
so much to actually collapse into black holesĀ Ā while the star was still forming. In contrast toĀ
stars today that would destroy themselves in theĀ Ā process, inside quasi stars, a deadly balanceĀ
could emerge. Gravity pressed the supermassiveĀ Ā star together, feeding the black hole and heatingĀ
the material falling in to such a degree that theĀ Ā radiation pressure kept the star stable. And soĀ
these quickly growing black holes might have beenĀ Ā able to consume the quasi star for millions ofĀ
years and grow far bigger than any modern stellarĀ Ā black hole. Black holes several thousand times theĀ
mass of the Sun and wider than the entire earth. These black holes might have becomeĀ
the seeds for supermassive black holes. Supermassive black holes So now, we arrive at the kings of ourĀ
universe, the largest single bodies inĀ Ā existence. The centers of most galaxies contain aĀ
super massive black hole, and they are monstrous. In the Milky Way we have Sagittarius AĀ
Star, a super massive black hole withĀ Ā about 4 million solar masses that is calm andĀ
collected and just does its thing. We knowĀ Ā it sits there because we can see a number of starsĀ
being thrown around by a seemingly empty spot.Ā Ā And despite its incredibleĀ
mass, itās radius is stillĀ Ā only 17 times our sun. Smaller than most giantĀ
stars, but millions of times more massive. Because Supermassive black holes are soĀ
massive and located at the center of galaxies,Ā Ā many people imagine them as being a bit likeĀ
the Sun in the solar system. An anchor thatĀ Ā glues everything else together and forces it intoĀ
an orbit. But this is a misconception. While theĀ Ā sun makes up 99.86% of all the mass in the solarĀ
system, SuperMassive Black Holes usually only haveĀ Ā 0.001% of the mass of their galaxy. The billionsĀ
of stars in galaxies are not gravitationallyĀ Ā bound to them, instead it is the gravitationalĀ
effect of dark matter which holds them together. Many supermassive black holes arenāt gentleĀ
giants, especially when they are feeding onĀ Ā the clouds of mass in their galaxy. The one at theĀ
center of the BL Lacertae galaxy is devouring soĀ Ā much material that it produces jets of plasmaĀ
accelerated to nearly the speed of light.Ā Ā If Earth were orbiting this huge body, it wouldĀ
seem 115 times larger than our Sun in the skyā¦Ā Ā and weād be burnt to a crisp in secondsĀ
by its glowing hot accretion disk. At this point black holes become so large thatĀ
stars seem ridiculously tiny compared to them. The galaxy Cygnus A has a super massive black holeĀ
with 2.5 billion solar masses and 14.7 billion kmĀ Ā wide, which would mean that if it took the placeĀ
of our Sun, it would swallow all the planets andĀ Ā stretch halfway to the edge of our Solar System.Ā
It is devouring so much mass and material that itĀ Ā churns its disk into a kind of magnetic funnel,Ā
spewing gas out making tremendous radio lobes,Ā Ā towering over the galaxy, half a million lightĀ
years in diameter. That is 2.5 Milkyways wide. Another pretty large Super Massive BlackĀ
hole sits in the galaxy Messier 87. ItĀ Ā has 6.5 billion solar masses and was theĀ
first black hole we got an actual photo of.Ā Ā Or rather of the glowing gas aroundĀ
the edge of a menacing shadow.Ā Ā This sphere of darkness is so largeĀ
that it covers our entire Solar System. And yet, there is a scale evenĀ
above these kinds of objects... Ultramassive black holes Now we reach the most massive black holes, perhapsĀ
the largest single bodies that will ever exist.Ā Ā These black holes have eaten so much that they'veĀ
grown to tens of billions of solar masses, theirĀ Ā gravity the engine for a āquasarā- an accretionĀ
disk shining brighter than thousands of galaxiesĀ Ā full of stars. So massive that they deserve aĀ
title of their own - Ultramassive Black Holes. The Ultra Massive Black Hole at the center ofĀ
galaxy OJ 287 is 18 billion solar masses. ItĀ Ā is so big that it has a Super Massive black hole,Ā
nearly forty times larger than sagittarius A star,Ā Ā orbiting it! This thing defies imaginationĀ
and is really hard to compare to anything.Ā Ā It can comfortably fit three SolarĀ
Systems side by side inside of it. Let us end this insane competitionĀ
and get to the king of kings. TON 618, a black hole that we can observeĀ
consuming galaxies worth of matter isĀ Ā shining with the brightness of a hundred trillionĀ
stars, visible from 18 billion light years away.Ā Ā It has an incredible 66 billion solar masses.Ā
A black hole so large that it would take lightĀ Ā a week to reach the singularity afterĀ
crossing the event horizon. About 11Ā Ā Solar Systems could sit inside of it sideĀ
by side. It may very well be the largestĀ Ā single body in the universe. But inĀ
reality, it is probably even larger.Ā Ā Since TON 618 is so far away, we only seeĀ
what it looked like 10 billion years ago. In any case, black holes are scary and mysteriousĀ Ā and gigantic. They will be here after everythingĀ
else dies, and growing larger and larger. So now let us do the trip again. FromĀ
the smallest possible black hole,Ā Ā all the way up to the largest. Letās try something new today,Ā
we can call it: āBehind the LiesāĀ Ā a short behind the scenes bit about theĀ
necessary inaccuracies in this videoĀ Ā because it's really not actually possibleĀ
to rank black holes like trading cards. How so? Well, while we have cataloguedĀ
millions of stars, we really only haveĀ Ā good data on a couple of dozen black holes.Ā
Thatās because black hole gazing wasnāt reallyĀ Ā a thing until 50 years ago ā and technicallyĀ
still isnāt, because we canāt see black holes. We can only derive their properties from studyingĀ
their gravitational effects on the matter aroundĀ Ā them, like the orbit of stars that come closeĀ
to them. This effect depends on the mass of theĀ Ā black hole, which we can approximate atĀ
the most basic level with Keplerās Laws.Ā Ā But this comes with hugeĀ
uncertainties and error bars.Ā Ā Then we have to convert mass to sizeĀ
next, which brings new uncertainties.Ā Ā For example, we calculated the radius from theĀ
mass using the Schwarzschild equation which forĀ Ā the sake of simplicity assumes black holes areĀ
perfectly round and donāt spin: a kind of blackĀ Ā hole that doesnāt really exist. The reality isĀ
that physics on these scales is a bit fuzzy. So some of the black holes we talked aboutĀ
here may be way smaller or way bigger. WeĀ Ā just donāt know for sure. We shimmied aroundĀ
this problem by comparing different sourcesĀ Ā with different kinds of values and usingĀ
different mass calculations to arriveĀ Ā at a standardized list that allowed usĀ
to be as accurate as humanly possible.Ā Ā You can look at all of this in our source doc. AsĀ
a result this script was written with the tears ofĀ Ā experts we drove crazy with our obsessionĀ
for the best values they could live with. In this process, tons of stuffĀ
got cut and didnāt make it intoĀ Ā the final video ā but luckily weĀ
found a way to not waste all of it: We created a lot of black hole merch, spanning theĀ
whole range from somewhat bonkers to more serious.Ā Ā This way we get to explore a topicĀ
from different angles ā and youĀ Ā get to continue having fun withĀ
black holes after this video ends.
The "behind the lies" bit at the end was really great!
So there are black holes so large that we have no idea at the moment what could have happened to cause them, aside from the possible existence of a theoretical star? Interesting.
Ah yes, the weekly dose of existential dread.
I don't think I've experienced Eldritch terror until Ton 618 was depicted.
Me : "Surely they can't get any bigger, right?"
Kurzgesagt : "Lol"
Me : "..."
Kurzgezagt is so great.
The song composed for the video is on Spotify, in case anyone else wondered
https://open.spotify.com/track/479piqfYJyfsuQ74HY9TMB?si=mxTM5jC6RbGkVxffXhuvdg&utm_source=copy-link&dl_branch=1
I sincerely hope they show these videos in classes. The visuals are so perfect for explaining more abstract concepts to people. Including myself!
The fact that the radius grows linearly with mass instead of mass1/3 still deeply confuses me
Edit: Imagine a woodmouse with a length of 10 cm and a weight of 20 g. If woodmice behaved like black holes, feeding the mouse until it was the mass of a human (100 kg) would not make it the size of a human -- it would grow to be 500 metres long! And in the same proportions as when it was mouse-sized!