What would happen if our planet
got too close to a black hole?
According to science fiction,
we'd be sucked into a parallel universe,
or maybe even the future.
But in reality,
it wouldn't be nearly that fun.
Instead, our planet would be ripped apart,
piece by piece,
starting with our atmosphere.
So what if we moved a little further back?
Instead of the black hole being right beside us,
we move it to the center of our Solar System.
This black hole has the same mass as our Sun.
If we were to place it next to our Sun,
the two objects would
orbit each other at a close distance,
about 1/10 the distance
between Earth and the Sun.
This would mean that our Solar System
was now orbiting a local point
with twice the mass of the Sun.
As a result,
the planets would have to orbit faster
to avoid getting pulled inwards.
A year on Earth
would decrease from 365 days to 258 days,
and the amount of energy from the Sun
would vary as it orbited closer to
and farther away from Earth.
Other than that,
life would be pretty well the same.
But what if we replaced our Sun
with a black hole completely?
Well, we'd have a lot more to worry about
than just the length of a year.
Which, by the way,
would be over in the blink of an eye.
The biggest problem we would face
if we replaced the Sun with a black hole
would be the absence of incoming solar energy.
The planet Earth would go completely dark.
Thanks to our planet's infamous
greenhouse gas effect,
the global temperature
wouldn't be reduced instantaneously.
But after the first week,
Earth's average surface temperature
would drop to 0°C (32°F),
and then to -101°C (-150 °F)
by the end of the first year.
You'd think that our planet
quickly becoming an ice world
would be bad enough,
but we're just getting started.
Without sunlight,
there would be no photosynthesis,
the process by which all plants generate food.
Small plants would die in a matter of days.
This would create a ripple effect
throughout the entire food chain,
causing us all to starve to death eventually.
But maybe there is a way we can get
usable energy from a black hole.
And it all starts with something called CMB.
CMB, also known as
cosmic microwave background,
is the weak radiation
left over from the big bang.
Theoretically, if a black hole spins fast enough,
it can compress the CMB radiation
into optical wavelengths,
the same wavelengths that
are emitted by the Sun.
The wavelengths would funnel
into a narrow beam,
and before you know it,
our planet would have usable
energy once again!
But there is a small catch.
The faster rotation of the black hole
would also pull the planetary orbits
in closer to the point of no escape.
For the planetary orbits to remain stable
and avoid being sucked up,
the orbital velocity of the planets
would need to be close to the speed of light.
This means that a year on Earth
would be over before the blink of an eye.
So much for your big New Year's Eve party.
But there's no time to worry about that
because we've got bigger issues
coming our way.
If any material, like
meteors, satellites, or space debris,
gets sucked into the black hole,
it will result in a blast of radiation
coming our way.
And when the radiation arrives at our planet,
it will blow away our atmosphere,
killing anything in its path.
So even though the Sun
can be annoying sometimes,
when it comes to things to orbit around,
we could do a lot worse.
The next time you look up at a sunny sky,
don't take it for granted.
It will disappear one day.
But that's a story for another What If.