Could we harness the power of a black hole Fabio Pacucci
Imagine a distant future when humans
reach beyond our pale blue dot,
forge cities on planets
thousands of light-years away,
and maintain a galactic web
of trade and transport.
What would it take for our civilization
to make that leap?
There are many things to consider—
how would we communicate?
What might a galactic government
look like?
And one of the most fundamental
of all:
where would we get enough energy
to power that civilization—
its industry, its terraforming operations,
and its starships?
An astronomer named Nikolai Kardashev
proposed a scale
to quantify an evolving civilization’s
increasing energy needs.
In the first evolutionary stage,
which we’re currently in,
planet-based fuel sources
like fossil fuels,
solar panels and nuclear power plants
are probably enough to settle other
planets inside our own solar system,
but not much beyond that.
For a civilization on the third
and final stage,
expansion on a galactic scale
would require about 100 billion times
more energy than the full 385 yotta joules
our sun releases every second.
Barring a breakthrough in exotic physics,
there’s only one energy source
that could suffice:
a supermassive black hole.
It’s counterintuitive to think
of black holes as energy sources,
but that’s exactly what they are,
thanks to their accretion disks:
circular, flat structures formed
by matter falling into the event horizon.
Because of conservation
of angular momentum,
particles there don’t just plummet
straight into the black hole.
Instead, they slowly spiral.
Due to the intense gravitational field
of the black hole,
these particles convert their potential
energy to kinetic energy
as they inch closer to the event horizon.
Particle interactions allow
for this kinetic energy
to be radiated out into space
at an astonishing matter-to-energy
efficiency:
6% for non-rotating black holes,
and up to 32% for rotating ones.
This drastically outshines
nuclear fission,
currently the most efficient
widely available mechanism
to extract energy from mass.
Fission converts just 0.08%
of a Uranium atom into energy.
The key to harnessing this power
may lie in a structure
devised by physicist Freeman Dyson,
known as the Dyson sphere.
In the 1960s, Dyson proposed
that an advanced planetary civilization
could engineer an artificial sphere
around their main star,
capturing all of its radiated energy
to satisfy their needs.
A similar, though vastly
more complicated design
could theoretically be applied
to black holes.
In order to produce energy,
black holes need to be continuously fed—
so we wouldn’t want to fully cover
it with a sphere.
Even if we did, the plasma jets
that shoot from the poles
of many supermassive black holes
would blow any structure
in their way to smithereens.
So instead, we might design
a sort of Dyson ring,
made of massive,
remotely controlled collectors.
They’d swarm in an orbit
around a black hole,
perhaps on the plane
of its accretion disk, but farther out.
These devices could use
mirror-like panels
to transmit the collected energy
to a powerplant,
or a battery for storage.
We’d need to ensure that these collectors
are built at just the right radius:
too close and they’d melt
from the radiated energy.
Too far, and they’d only collect
a tiny fraction of the available energy
and might be disrupted by stars orbiting
the black hole.
We would likely need several Earths
worth of highly reflective material
like hematite to construct
the full system—
plus a few more dismantled planets
to make a legion of construction robots.
Once built, the Dyson ring
would be a technological masterpiece,
powering a civilization spread
across every arm of a galaxy.
This all may seem like wild speculation.
But even now,
in our current energy crisis,
we’re confronted
by the limited resources of our planet.
New ways of sustainable energy
production will always be needed,
especially as humanity works
towards the survival
and technological progress of our species.
Perhaps there’s already a civilization
out there
that has conquered
these astronomical giants.
We may even be able to tell
by seeing the light
from their black hole periodically dim
as pieces of the Dyson ring pass
between us and them.
Or maybe these superstructures are fated
to remain in the realm of theory.
Only time— and our scientific ingenuity—
will tell.