This Episode is sponsored by Brilliant Black Holes are amongst the most dangerous and destructive things in the Universe. So
letâs go live on one! So today we return to Outward Bound series
to look at Colonizing Black Holes. We talk fairly often on this channel about
advanced civilizations using black holes in various ways. But weâre usually talking
either about artificial micro-back holes that emit Hawking Radiation and need to be fed
constantly so they donât disappear, or about civilizations so far forward in time that
black holes would be prevalent, while what we call âstarsâ would be ancient history,
part of a brief bright era when the universe was still settling down from the Big Bang.
But today, we are going to talk about how and why black holes might become the preferred
places for much nearer-future civilizations to colonize, even while stars still burn and
uninhabited planets are abundant. In a lot of science fiction, a ship stumbling across
a black hole is cause for panic, but in reality the crew would probably be popping corks on
the champagne, because thatâs some very valuable real estate they just found!
To understand why, letâs talk briefly about what our descendants would be looking for
in a place to colonize. Stars are useful fundamentally as power sources. Earth is basically self-sufficient,
except for the light we receive from the sun, which keeps our planet comfortably warm and
powers our entire ecosystem. But that power doesnât originate on the surface of the
sun that we can see. That goes on deep down inside, where fusion turns hydrogen into helium
and produces lots of lethal gamma rays. Those get absorbed and re-radiated as lower energy
longer wavelength photons many times by the layers above, until that energy is eventually
emitted at the surfaceâmostly as visible light and infrared in the case of our Sun.
Many of our colonization methods rely on collecting that light, and weâve discussed lots of
ways to concentrate or diffuse that light, to let us settle at distances of our choosing
from the star. Other colonization plans involve replicating sunlight in our habitats using
other energy sources. Fusing hydrogen into helium produces millions of times more energy
than any chemical process does, but controlled contained fusion is still something that eludes
us. We do achieve fusion in hydrogen bombs, which
are often compared to the sun, but current hydrogen bombs require rare isotopes like
deuterium, tritium, or lithium deuteride, the ones that are easiest to fuse. So a nice
reactor you can dump common hydrogen into and get electricity from is quite a ways offâand
it would still only release less than one percent of the energy available in matter,
Einsteinâs E=mc². Black holes are much easier and more efficient.
There are several ways to get power from a black hole, and which one youâd use depends
on your level of technology and the size of the black hole. You can check out our video
about Black Hole Ships from a few weeks back if youâd like to learn more about those
methods. But for black holes of the size weâre discussing today, the size you would colonize,
the easiest method is to simply drop matter in and collect the x-ray radiation pouring
from the accretion disk. Matter in the accretion disk is compressed
with such force and moving so fast that friction produces immense heat, which for an average
natural-size black hole would be radiated in the x-ray part of the spectrum. This is
what we believe powers quasars. So a scaled-down version of the brightest objects in the Universe
would be the power plant of your colony. Black holes also have potentially enormous
value for industrial uses besides just being a great power source. They are the perfect
way to dispose of anything you donât feel is safe or economical to recycle or otherwise
safely dispose of, as a black hole doesnât care what kind of matter you feed it, just
the amount. People often talk about dumping radioactive waste into the sun, which is not
a great idea for reasons weâll save for another day, but in a black holeâs case,
itâs actually a highly profitable way to dispose of dangerous material.
As we discussed in Black Hole Ships a few weeks back, these objects are also handy for
space travelers because they allow a way to change directions with minimum fuel. You can
fly close to any massive body to alter your course or give yourself a little speed boost,
but the sharper the turn you want to make, the closer the pass youâll have to make--which
might be too close to the heat of a star if not inside the star itself.
And contrary to whatâs depicted in most sci-fi, you can fly closer to a black hole
than you can to a star of equal mass because itâs much cooler and doesnât have all
that pesky stellar atmosphere and solar wind that youâd rather not encounter at high
speed. Though Iâll note that black holes are not
the only dead stars handy for space travel. When a star starts dying it usually spends
a fair amount of time as a red giant, and those are actually so thin you could run a
ship through their atmosphere as a means of slowing down. Not our topic for today, but
since slowing a ship down is one of the biggest issues with interstellar travel, these offer
a partial solution. You can push on ships with lasers to accelerate
them, but there will be no laser to slow you back down at an undeveloped destination, so
that constrains how fast you can travel to uncolonized systems. Any fuel you have to
save for deceleration at the end canât be used for acceleration along the way. Red giants
might be ideal vanguard systems for colonization because you reach them at higher speeds than
other, neighboring systems, letting you set up as the first port of call for that region
of the galaxy. In this same way, black holes make good waypoints
for distance places, as you can head in their direction and use them to alter your course
and boost your speed, and they can be used to slow down too. Indeed, one you can see
a long way off is likely jetting relativistic matter off its poles and you might be able
to use conventional sails or magnetic sails to use that for braking drag or an added boost.
So such places might naturally tend to be the first distant places we visit and settle.
And once youâve colonized it, assuming youâve got some raw materials nearby, which is quite
likely as even the supernova that produced it would have been powerful enough to destroy
the original outer planets it probably had, youâve got a giant power plant on hand and
raw materials to feed it and build with. Initially you wouldnât want to live too
close, though again not for fear of gravity. The method youâre likely to use for power
generation is to throw matter around a black hole to form an accretion disc, which emits
huge amounts of X-ray radiation. So if you want to be close youâll have to wrap that
thing in radiation shielding and to prevent any large chunks of matter falling in and
producing big blasts of X-rays. Of course if youâre building a shield, you
might want to throw some dirt on top of it. Dirtâs good radiation shielding too, and
we can add air and water and artificial lighting and presto, new planet. Except itâs kind
of huge one. Your typical stellar mass black hole is a million or more times as massive
as Earth, so if you build a shell around it for normal Earth-gravity, it would be a shell
a thousand times wider than Earth and a million times larger in surface area, a true Mega-Earth.
I should note it would also have an escape velocity 32 times higher than Earthâs, 354
km/s instead of 11.2 km/s. The gravity well is bigger and deeper, for all that the force
on you is the same as on the surface of Earth. Easy to visit, but hard to leave, making it
quite the tourist trap. Now the means for doing this shell is one
weâve discussed many times on this channel and thatâs the orbital ring. Our episode
on Colonizing the Sun gives a full discussion of how to do that around a massive object,
but basically, by creating a hollow hoop of matter that does not orbit the planet or star
or black hole beneath it, but merely wraps around it, then spinning another hoop or a
stream of matter inside it at faster than normal orbital speed, we get a big stationary
ring we could walk around on. We could make many of them, cocooning that object with a
mesh and then presto, shell world! In this case youâd probably have a lower
shell from which to dump matter into the black hole and absorb the radiation to make power.
You might have several habitable upper layers too. Such planets have to be very big because
black holes are as massive as large stars, and since gravity increases with mass and
falls off with distance, and you have to be a lot farther from a black hole than from
the Earthâs center for the gravity to be walkable.
Black holes often gain mass or even merge with other black holes, as we often find black
hole candidate stars, supergiants, growing up together in big clusters. So there are
going to be some very large ones of hundreds of even thousands of solar masses. Shells
around them work just fine too, but they get even harder to leave, even though the gravity
on that shell is presumably the same as Earthâs surface, the escape velocity will keep rising.
As you probably know, time slows down in bigger gravity wells and this slowing can be approximated
as the same as the escape velocity in terms of the classic special relativity effect of
time slowing on a fast spaceship, at least when youâre not too close to the event horizon.
So a shell that had an escape velocity of 1% of light speed has the time running slower
on it basically the same as a spaceship traveling at that speed.
Which in truth is very little, your clock would only lose about 4 seconds a day, or
about 26 minutes a year, and would require a mass of several thousand solar masses. Such
black holes are not very common, though considerably larger ones reside at the cores of most galaxies.
On our first example, the simple Mega-Earth built around a black hole of a few solar masses,
with an escape velocity of merely 354 km/s, time would only be running about 22 seconds
slow per year. But for those big galactic core black holes,
often running into the millions of solar masses, a shell around those, what we call a Birch
Planet, running a trillion times the mass and surface area of Earth, would have an escape
velocity a thousand time that of Earth, about 4% of light speed, and youâre losing over
a minute every day. Still not a lot, but such an object is so huge that its tidal forces
are tiny even where the gravity is high, so an object placed at 100 times the Earthâs
gravity, a tenth as far from the center as the planet-shell, would actually be losing
a few days a year. This can go way higher though, as black holes
can be made much bigger. That monster at our galactic core of a few million solar masses
is not even a percent of a percent of our galaxyâs mass. It will only grow with time
too. One which had swallowed up most of its galaxyâs mass would be having an escape
velocity around half the speed of light and time running a good deal slower, and at this
point the spaghettification effect on matter near the event horizon is practically none.
Those willing to experience higher gravity would experience much slower time.
It also means you could drop down into that black hole without being killed in the process,
indeed you could do this on a much smaller one too. We donât know what goes on down
inside them but the various options in this or that theory would include some that might
make this a good idea, assuming you had no desire to return to the universe outside,
which might indeed be the case by the time monster-sized black holes like this were the
norm, as the Universe would be petering out by then.
On these very large ones though, where you are likely including multiple layers of shells,
time would be running significantly faster or slower depending on which layer you resided,
and would be much more extreme if you were in the higher gravity areas, if for instance
your biology was adapted to a few gees or if you were post-biological and could endure
hundreds or even thousands of gees. Weâve explored those possibilities quite
a bit in our Civilizations at the End of Time series, but for this episode, letâs get
back closer to the here and now. A question arises as to where youâd get
these black holes from. Itâs worth keeping in mind that black holes arenât terribly
common. Only around 1 in 1000 stars that forms is massive enough to become a black hole,
but that still means we ought to have at least 100 million of them in our galaxy now, with
of course a super-massive one in the center, 30,000 light years away. The closest one we
know of, V616 Monocerotis, is about 3000 light years away, with the famous Cygnus X-1 being
the second closest at 6000 light years away. But these are probably not be the closest,
only the closest known. While stars are not randomly placed by type, we have many stars
massive enough to form a black hole closer than either of those, and those are just living
ones. Remember we said 1 in 1000 that forms is big enough to die a black hole, but such
stars live short lives, hence their rarity among our neighbors, they form and die after
just a few million years, as opposed to their black hole remnants, which will live on for
the next best thing to eternity. Although talking about these stars living
briefly and dying as black holes, given the huge value of black holes, and other âdead
starsâ for that matter, seems an increasingly flawed definition. Even the name, black hole,
contains two words that are both so pessimistic⌠and also both incorrect. Itâs like calling
an island a dead volcanic eruption, technically true but a weird and short-sighted way to
regard a potentially lush tropical isle thatâs far more amenable to being colonized than
a typical erupting volcano. Anyway, by default weâd expect there to
be hundreds of black holes for every massive enough star we can see alive now, though of
course quite a few might have merged with siblings into more massive black holes by
now or been ejected from the galaxy. That said, while the nearest we can see right
now is 3000 light years away, thereâs a couple hundred million stars in that volume,
so thereâs presumably a couple hundred thousand black holes in that volume too. Probably somewhat
fewer due to mergers, ejections, and the galaxyâs supergiants not really being evenly distributed.
Thereâs around 15,000 stars within just a hundred light years of us, our targets for
a nominal first wave of interstellar colonization, and it would be a bit surprising if there
wasnât at least one black hole in that region. Black holes are obviously hard to see, since
they are only detectable by either wobbling their binary companion if they have one or
if they are sporting a significant accretion disc of matter falling into them and giving
off huge amounts of radiation. They wouldnât sneak up on you though, theyâre hard to
see hundreds of light years away, same as planets, but youâd know one was there, from
its gravitational effects, long before you were close enough to be in any real danger.
While we might be colonizing black holes in our stellar neighborhood in just a thousand
years or so, itâs quite likely weâll be using them for colonization a lot sooner.
Weâve discussed some ways of making black holes in the black hole ships episode, and
some require no particularly advanced technology, just a lot of infrastructure, which a growing
interplanetary civilization a few centuries from now might have. Although the power requirements
are far larger for making bigger black holes, the technical challenges are a lot smaller.
Weâve talked a lot about kugelblitz black holes, ones of relatively low mass and short
lives that give off huge amounts of power by Hawking Radiation, but it might turn out
weâre limited to making ones no less massive initially than a fairly small asteroid. Of
course once theyâre large enough you can jam matter into them, thereâs no longer
a power requirement for making them bigger, quite the reverse, youâre generating huge
amounts of power while you do it. If you effectively have a point-like object
of huge mass, and even one of Earthâs mass is only the size of marble, you have a handy
source of artificial gravity. You could drill a hole into Mars and drop one down of the
right mass, and suddenly have Earth-like gravity on the surface. Mars is about half the diameter
of Earth and about 11% of Earthâs mass, for that radius it would need about a 28%
of Earthâs mass for Earth-like gravity, youâd presumably get that other 17% from
one of our gas giants or the Sun. Transport would be no problem, since a black
hole youâre feeding matter into is as easily adapted into a shipâs drive as a power plant,
as we discussed a few weeks back. Handily, while the gravity is now Earth-like, the escape
velocity is still decently lower than Earthâs, just 8km/s, and orbital speeds would only
be about 5 km/s, much handier for things like spaceplanes, which weâll be having an episode
on next week. This trick works as well on Mercury or Venus
or Pluto or our own moon or any of the other moons. Or for that matter small asteroids
or artificial spherical habitats. One might argue itâs a bit mass wasteful but they
are good power generators and older ones used as starship drives that had grown in mass
too much might get retired to serve as the cores of micro-planets. We also only mostly
want hydrogen and helium, the overwhelming majority of regular matter in this universe,
for power generation in suns or artificial fusion reactors, but fusion power is redundant
if youâve got artificial black holes that are way more efficient.
In terms of size, for such things, youâve got limits for both the top and bottom but
itâs very broad. Go too big, and a shell at normal Earth gravity would be dangerously
close to the event horizon, or even in it, but thatâs way up at galactic mass. Go too
small, and the black hole is emitting so much Hawking radiation that normal gravity would
put you in a place too hot to live, but thatâs getting down to a planetary size parallel
to a modest backyard. If youâve seen the Rick and Morty episode where they go hide
on a microplanet they can walk around, yes that is possible with this technique.
With one caveat, as mentioned, a black hole dumped into Mars to give it Earth-normal gravity
still leaves it with a lower escape velocity, still more than enough to hold an atmosphere,
which is mostly about creating a stronger magnetosphere anyway, but that effect gets
bigger as we get smaller. If your micro-planet only has an escape velocity about the same
as the root-mean square speed of room temperature air, itâs all going to leak away very quickly.
So youâd still need to dome it over, which arguably removes half the appeal such a planet
has over a classical rotating habitat where thereâs no natural sky.
Of course you could still have windows and skylights and could walk around outside in
a space suit with normal gravity. Now a planet isnât going to keep its atmosphere
just because itâs escape velocity is higher than the speed most air particles zip around
at, it will still leak fast it just wonât blow off rapidly if you puncture the dome,
but if youâre curious, an asteroid about a dozen kilometers wide, and about a millionth
Earthâs mass with its artificial black hole in the basement, would have an escape velocity
of about Mach 1 and could probably get away with fairly minimal airlocks for spaceports.
Thereâs some great examples of such worlds in Alastair Reynoldsâ Revenger series, where
the black holes in these worlds get called Swallowers. Amusingly, most readers apparently
miss that all the spaceships traveling to various other worlds in that book via light
sails are actually just roaming around a single solar system in a partial Dyson Swarm, probably
unsurprisingly, most channel regulars here did not miss that. So you can fill all your moons and larger
asteroids up with such black holes and get normal gravity, and grind the smaller asteroids
up to make artificial shells or regular cylinder habitats. Very handy approach for mining an
asteroid too since youâve got all the power you need for running your mining and manufacturing
and launching. That is still a lot of mass but again itâs
mostly hydrogen and helium which we canât build out of and which we wouldnât need
for fusion. One big issue though, first, you are still using that mass for power and once
itâs down in the black hole youâre not getting it back unless youâre willing to
wait a long, long time, and longer the bigger it is. Even a black hole with only a millionth
the Earthâs mass, itself barely bigger than an atom, is going to live over a billion,
trillion times longer than our Universe is old. Which is actually fine if you want to
be storing power for after the Sun goes out, but is a long term investment to say the least,
and bigger ones live way, way longer. We can cheat though, instead of using a single
one we can jam several into the same spot, just far enough apart they donât merge.
One of, say, a 120 megatons, would be coming due about the time our Sun burned out, while
those you might want to use as a ship drive might leak out in thousands or million of
years. People often suggest the main currency of
the future would be matter or energy and micro black holes make great long term bonds, since
you can store power in them as a perfect battery for very, very long times with very, very
little leakage. Makes them a great way to store your treasury, since a black hole is
harder to break into that Fort Knox⌠or at least harder to break out from with your
loot. One problem though, especially for smaller ones, is itâs going to be hard NOT to generate
power while youâre fattening them up. You might wonder how thatâs a problem, but
consider, if I am making black holes for the space habitat market, and someone puts in
an order for a billion ton black hole to be delivered next month, if even 1% of that feed
matter gets radiated away as energy while Iâm doing this, thatâs a trillion, trillion
joules of energy released, enough to illuminate Earth for an entire year, or power out current
global economy for 20,000 years. And youâd need 6 trillion of those to make an Earth-sized
Shellworld or the equivalent land area of many smaller micro-planets. That would also
represent the entire Sunâs output for a few thousand years. I mean thatâs exactly
why these are such ideal power plants. Now, handy thing about a black hole is so
long as youâre aiming the feedstock right down its gullet, thereâs no energy splash,
no accretion disc, etc, and thatâs viable for one of modest size, and of course we can
always find a use for power. You can use it for accelerating spaceships away or power
transmutation to turn one element you have in abundance into another you want more of.
Getting rid of heat is an issue but you can be doing this in the outer solar system, even
way out beyond the Kuiper Belt, where swarms of such black hole factories would enjoy thousands
of times more radiating area than in the inner system. And itâs also the ideal place for
running all your interstellar shipping and colonization out from, since high speed collisions
are less of a concern far from your core civilization. So I could easily imagine an inner solar system
with our classic planetary colonization and asteroid and cylinder habitats slowly forming
a conventional Dyson Swarm where, far out from the Sun, a growing black hole based economy
was sent out and receiving interstellar ships and exporting black holes to the inner system
to slowly replace or augment the more standard habitats and worlds there, each with little
black holes in their basement serving as either a current power source or a long-term treasury
for the End of the Universe. Of course, the outer solar system is a great
place to be putting a defense network for your inner system, as we discussed in Colonizing
the Oort Cloud, and beyond supplying power for such defense stations, black holes can
be terrifying weapons. But weâll get to that in a few weeks.
So we were talking about black holes and escape velocity today and how you could use them
to alter your course or gain a speed boost. Thereâs an excellent quiz on Black Holes
in Brilliantâs Astronomy course, and their Astronomy quizzes are a great way to expand
your knowledge on that topic and get comfortable working with a lot of the core concepts we
often build our discussions of our future out in the galaxy off of.
Brilliant uses a mix of interactive visualizations and illustrated and animated problems in short
quizzes to help you learn about topics like that or how to slingshot a ship around a massive
body that a dry textbook or lecture just doesnât do as well, and it lets you do it at your
own pace from the comfort of your own home, but also as part of a learning community that
you can talk with for help or discussion. The most important part of learning is keeping
it fun and interesting, and they do great job of that, from their interactive courses
to their daily challenges, which help to stimulate your thinking and connect to expanded courses
if one of those problems grabs your interest. Learningâs best done every day, and those
daily challenges are an excellent way to warm up the brain and introduce you to exciting
new topics. If youâd like to learn more science, math,
and computer science, go to brilliant.org/IsaacArthur and sign up for free. And also, the first
200 people that go to that link will get 20% off the annual Premium subscription, so you
can solve all the daily challenges in the archives and access every course.
So weâll get to our upcoming schedule on Youtube in just a moment, but first, we have
an upcoming bonus episode coming out that wonât be on Youtube.
Iâm not sure if Iâve mentioned it before but a little over a year ago I was invited
to join a digital creator community called Standard that had got founded by the creators
of Kurzgesagt and CGP Grey shortly before that. Itâs principally other educational
channels, and while we all love Youtube and arenât leaving it, their algorithm really
isnât optimized with those kind of shows in mind and it often limits what we can do
or try out so that Youtubeâs algorithms donât bury our video, or our channel. So
we created Nebula, a streaming video platform that we control, so we can use it to try new
things, explore new formats, and share more behind the scenes content.
To honor that rolling out, tomorrow weâll be premiering a look at the Paperclip Maximizer,
the concept of a runaway artificial intelligence, and an idea called Instrumental Convergence,
that even intelligences with very peculiar goals, like making paperclips, will often
mimic goals and behaviors of creatures with different goals, like survival.
Nebula is only five bucks a month, going to the creators to fund new original content,
and to improve the service, which is brand new. But you can watch that episode and others
from folks like Kurzgesagt and Real Engineering for free, with a seven-day trial.
Visit watchnebula.com and get a free seven day trial to check out the Paperclip Maximizer,
and stay tuned for all of the great stuff weâre working on for you.
As mentioned, todayâs episode is part of short series on black holes that we started
a few weekâs back with Black Hole Ships, and weâll be continuing that in three weeks
with Weaponizing Black Holes, and weâll look at some of the awesome and downright
terrifying ways these might be deployed in the far future.
But next week weâll be returning to the Upward Bound series to look at Space Planes,
particularly the Skylon spacecraft, and ask what technologies weâd need to let you take
of from your garage and fly straight to orbit, or to the Moon or Mars, in your own personal
spaceship. For alerts when those and other episodes come
out, make sure to subscribe to the channel. We also have our monthly Livestream Q&A coming
up this weekend, Sunday May 26th, at 4pm Eastern time, and I hope to see you then.
Until next time, thanks for watching, and have a great week!
Too busy to see the whole video but what I did watch is boggling. We are at the infancy of space faring and colonization of the solar system. It's hard to imagine the advances we would have to make to harness a black hole.