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.