They’re the most mysterious and frightening objects in outer space, capable of breaking
down and devouring anything in their path. Some are millions of times more massive than our sun,
and they’re scattered all across the cosmos. Upon learning about black holes for the first time,
then, you may have (with good reason) wondered whether any of them could ever threaten Earth?
This is Unveiled, and today we’re answering the extraordinary question:
could black holes travel through the universe?
Do you need the big questions answered? Are you constantly curious? Then why not subscribe to
Unveiled for more clips like this one? And ring the bell for more thought-provoking content!
Just a few months after Albert Einstein published his famous theory of general relativity in 1915,
physicists studying his field equations were astonished to discover solutions
that described what we call today “black holes”. At these bizarre points in spacetime,
the laws of physics broke down, with matter condensing to a singular point of infinite mass.
It took many more decades for additional science experiments and theorizing to definitively prove
the existence of black holes. And the first actual black hole, Cygnus X-1,
wasn’t actually identified until 1971. But, nevertheless,
talk of these cosmic monsters has been a near constant now for more than one hundred years.
Fast forward to today, and not only have we actually photographed a black hole,
but we know they’re extremely common throughout the universe. There are thought to be millions of
them in the Milky Way alone, which is just an average-sized galaxy - in the grand scheme of
things. And, because any sufficiently massive star can collapse into a black hole upon its death,
there are billions or even trillions of stars out there in the universe that will one day
share this fate. There are, then, many, many more black holes to come!
Pretty much ever since black holes became known to the wider public,
many people have been somewhat afraid of them. And it’s easy to see why. These things
are difficult to understand and almost completely impossible to even imagine… particularly the vast,
supermassive black holes that lie in the heart of almost every galaxy. But as scary as black holes
are, we actually rely on them to keep our galaxy functioning. It’s clear that they’re an integral
part of the universe’s entire ecosystem – if it could be called such. But, that said, the big
question still remains; could a black hole ever threaten us here on Earth? If they’re out there
in such huge numbers in the universe, including throughout the Milky Way, is it beyond the realm
of possibility that a black hole might someday wander close enough to destroy not only Earth,
but every other part of the solar system as well? Well, black holes absolutely do move through
space, just like everything else. There are absolutely no static objects in the universe.
From the smallest molecules to the largest stars, everything is swirling and turning all the time.
Amid this primordial spinning, clouds of atoms are drawn together, spinning faster and growing
denser, until they eventually form the objects we’re familiar with. Pieces of rocky debris
and metal come together to form terrestrial planets, while fields of hydrogen become gas
giants and stars. And, in time, stars that are large enough will collapse into a black hole.
Throughout all these different processes, celestial bodies all continue to move. The
Earth moves around the sun, the sun moves around the galactic center,
and the galaxy itself, including the supermassive black hole at its heart,
circles a common center of mass between the Milky Way and neighboring galaxy Andromeda.
As for black holes, they can be caught up in all of this in more expected ways,
at the center or finely balanced systems… and they can also orbit normal stars, themselves, and even
other black holes in “binary black hole” systems. There are even black holes in binary systems very
close to Earth. And the closest black hole right now is thought to be just 1,500 lightyears away,
although this is disputed. Otherwise, the closest would be some 3,300 lightyears away.
But still, that’s relatively close in a Milky Way that’s about 100,000 lightyears across.
The fact that we’re here today to watch videos all about black holes proves that all this happens
safely out there, for the most part, at least as far as we’re concerned. But there is such a
thing as a rogue black hole, and that’s where the real danger may lie. Rogue black holes are also
known as “orphan”, “nomad”, or “wandering” black holes. They’re bizarre, unattached singularities
drifting idly through the galaxy without appearing to orbit a larger center of mass.
We finally detected such a black hole in early 2022, roughly 5,000 lightyears away and moving
at about 28 miles per second. The reason it took so long to find one of these black holes is that
they’re so isolated. Occupying interstellar space, they don’t have bright objects nearby
with which to regularly interact. The reason we know of so many binary systems that include
black holes is because it’s far easier to detect a black hole when it’s in the proximity of a star.
We can’t actually see black holes, so we have to detect them thanks to their effects
on neighboring bodies. And this is extremely difficult with a black hole that’s gone rogue.
Fortunately, though, rogue black holes are still supposedly far less numerous than regular black
holes that have host systems. Scientists currently estimate that there are only a dozen in the Milky
Way. And 5,000 lightyears - the distance between us and the first known rogue black hole - is still
a long way. Even if this particular black hole were heading straight for us and traveling at
the speed of light – which it almost certainly would NOT be doing – it would take thousands of
years for it to reach us. As this is the first rogue black hole we’ve definitively identified,
it could well be the one nearest to us, and therefore we don’t have much to worry about.
But, on the other hand, it’s true that aside from the sheer unlikeliness, there’s really nothing
else stopping a rogue black hole from someday invading our solar system. The good news, then,
is that if a black hole ever came this close, we’d definitely see it coming. The bad news,
however, is that if there was a black hole on a collision course with our solar system, then
there’d really be nothing we could do about it. The arrival of a black hole in our system
wouldn’t necessarily guarantee our demise. But the outlook wouldn’t be good. A supermassive black
hole would be devastating, and even a regular, stellar-mass black hole would cause chaos.
It is possible that a black hole could settle into a regular orbit around the sun.
It isn’t likely though, because even a regular black hole would be more massive – and therefore
gravitationally stronger – than the sun. The sun isn’t big enough to become a black hole, nor is it
big enough to wrangle one. A more likely scenario is that the solar system would reorganize itself
around the black hole instead of around the sun. This would destroy any planet that gets too close,
but it would also destabilize the system and could cause interplanetary collisions.
No matter the scenario, the arrival of a black hole would badly destabilize Earth’s orbit,
potentially rendering it uninhabitable. If Earth were pushed too far away from the sun,
it would grow too cold. Drawn too close to either the sun, or the black hole,
Earth could become far too hot, radioactive, or both, to support life. It’s the chaos that an
invading black hole would bring to the objects in the solar system that is the real danger.
Even if the black hole were somehow able to pass through the solar system and exit it again,
continuing to orbit the galactic center, it would have destabilized everything in our system in the
meantime… with potentially deadly consequences. Finally, what about rogue black holes outside of
our galaxy? In addition to black holes within our galaxy, and in others, there could also be black
holes that exist between galaxies. In 1997, the first “intergalactic stars” were proven to exist:
stars that drift through space without being gravitationally bound to a particular galaxy.
Previously it was believed that there were no stars in these dark regions, because the
materials to form stars don’t exist out there. But physicists now believe that intergalactic stars
are stars that have gotten lost, in a way, stranded out there after galactic collisions
that essentially left them homeless. There are probably trillions of them… and, remember,
where there are stars, there are also black holes, roaming forever through the dark. Suffice to say,
intergalactic black holes pose even less of a threat to us here on Earth
than interstellar ones do, but they’re quite an ominous prospect nonetheless!
Like every celestial object,
black holes travel through space, and some of them are closer to Earth than others.
And that’s why, like it or not, black holes CAN and DO travel through the universe.
What do you think? Is there anything we missed? Let us know in the comments, check out these other
clips from Unveiled, and make sure you subscribe and ring the bell for our latest content.