From turning things into spaghetti to erasing
your past, these are 10 fascinating things
you probably didn’t know about black holes:
10. They weren’t discovered by Einstein
Even though Albert Einstein predicted black
holes in 1916 with his general theory of relativity,
he wasn’t the first one to hypothesize about
these fascinating astronomical objects. It
was actually English clergyman and natural
philosopher John Mitchell who first proposed
the existence of black holes in a paper published
in 1783, calling them "dark stars". Mitchell
argued that particles emitted by a star would
be slowed down by the star’s gravitational
pull and calculated that this would be the
case with a star more than 500 times the size
of the Sun. He also predicted that these objects
would be invisible since light would not be
able to escape from them.
Mitchell suggested that there might be many
"dark stars" in the universe, which proved
to be true since astronomers now know that
black holes exist at the centers of most galaxies.
What’s even more incredible is that Mitchell
was able to accurately predict that we could
detect "dark stars" by looking for star systems
which behaved gravitationally like two stars.
Centuries later, astronomers confirmed his
prediction and determined that all of the
candidate stellar black holes in our galaxy
are part of binary star systems. Unfortunately,
Mitchell’s ideas weren’t well received
at the time and he died in obscurity. It wasn’t
until the 1970s that his writings re-surfaced
and his contribution to the science of black
holes was recognized.
9. They make sound
You were probably taught in school that there
is no sound in outer space, since space is
a vacuum and sound waves can’t travel through
a vacuum. Well, that’s not completely true.
Distortions in the fabric of spacetime, also
known as gravitational waves, cause the spacetime
to vibrate and produce sound when they pass
near object with mass. With special equipment
such as Laser Interferometer Gravitational-Wave
Observatory, or LIGO, astronomers can amplify
these faint sounds billions of times and actually
hear what the universe sounds like.
In 2003, NASA astronomers using Chandra X-ray
Observatory discovered for the first time
sound waves coming from a supermassive black
hole. The sound was the deepest one ever detected
from any object in the universe and it came
from hundreds of thousands of light years
away. This “noisy” black hole is located
in the Perseus cluster of galaxies - one of
the most massive objects in the known universe
located 250 million light years from Earth.
The pitch of the sound generated by the supermassive
black hole translates into the note of B flat.
However, a human ear would have no chance
of detecting this cosmic music because the
note is 57 octaves lower than middle-C and
has a frequency over a million billion times
deeper than the limits of human hearing.
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8. They come in different sizes
When most people think of black holes, they
imagine giant areas in outer space that suck
in everything around them. But black holes
actually come in different sizes – from
microscopic to supermassive. Oh, and they
don’t actually suck, but more on that later.
The largest type of black hole is known as
the supermassive black hole. These gargantuan
objects can reach sizes equivalent to anywhere
between hundreds of thousands to billions
of solar masses. The most massive black hole
ever discovered is TON 618, which is thought
to weigh in at 66 billion times the mass of
the Sun! The smallest black hole on the other
hand, is only 15 miles (or 24 kilometers)
in diameter and weighs in at about 3.8 times
the mass of the Sun. Even though the existence
of micro black holes is still purely theoretical,
some scientists believe that tiny black holes
may be artificially produced. In fact, physicist
John Archibald Wheeler has calculated that
a very powerful hydrogen bomb using all the
deuterium in all the water on Earth could
generate a micro black hole.
7. They don’t suck
Black holes are often portrayed in science
fiction movies as tunnels to other dimensions
that suck everything in sight. However, this
is yet another common misconception about
black holes. Suction is caused by pulling
an object into a vacuum, which is not what
black holes are. Black holes are formed when
a very massive star reaches the end of its
life and explodes as a supernova. The core
of the dying star compacts into an infinitely
dense mathematical point with an extremely
strong gravitational pull.
So in other words, black holes pull, not suck.
They simply interact with matter through gravity,
just like any other object in the universe.
Objects that come near the event horizon can
be said to be getting pulled in or more precisely
falling into the black hole as a result of
its powerful gravitational force. And for
things to fall into a black hole, they must
be travailing at a speed where their orbit
intersects the event horizon, which is rarely
the case or those object wouldn't truly be
in orbit to begin with.
6. They turn everything into spaghetti
So what exactly happens when objects approach
the event horizon? In a lecture titled “Into
a Black Hole”, Stephen Hawking theorized
about what would happen to a fictional astronaut
who falls into a black hole. In Hawking’s
own words, “falling through the event horizon
is a bit like going over Niagra Falls in a
canoe. If you are above the falls, you can
get away if you paddle fast enough, but once
you are over the edge, you are lost. If you
fall towards a black hole feet first, gravity
will pull harder on your feet than your head,
because they are nearer the black hole. The
result is, you will be stretched out longwise,
and squashed in sideways. If the black hole
has a mass of a few times our Sun, you would
be torn apart, and made into spaghetti, before
you reached the horizon.”
In astrophysics, this process is known as
spaghettification. Since black holes have
extremely high masses concentrated in a very
small radius, the gravitational force near
a black hole is enormous. The extremely powerful
gravitational field of a black hole tears
at the matter's very atomic structures, stretching
and compressing horizontally all objects into
long thin shapes - much like spaghetti!
5. They break the laws of physics
Have you ever wondered what is at the center
of a black hole? Well, no one knows for sure
since the insides of a black hole are impossible
to observe. However, scientists predict that
in the middle of every black hole lies a spacetime
singularity. Spacetime singularity is a location
in spacetime where the gravitational field
of an astronomical object becomes infinite
and the laws of physics as we know them cease
to exist.
Black hole is what happens when mass is compacted
into a single dense point. The density of
the black hole is its mass divided by its
volume, and since the volume of a single point
is zero, you're dividing by zero – which
is impossible! In other words, our current
knowledge is insufficient to explain the phenomenon
of infinite density and even though singularities
appear in many theories in physics, they are
usually taken as a sign that the theory has
a missing piece.
4. They may create new universes
Even though the Big Bang theory is the leading
scientific explanation for the origin of the
Universe, some astrophysicists have proposed
that the Universe started from a small singularity
inside of a black hole. This idea was first
put forward in 2013 by physicists from the
Perimeter Institute for Theoretical Physics
in Waterloo, Canada. According to this theory,
our universe burst into being when a star
in a four-dimensional universe collapsed into
a black hole. In other words, what we perceive
as the Big Bang could be the three-dimensional
mirage of a collapsing star inside of some
other universe profoundly different form our
own.
In our three-dimensional universe, black holes
have two-dimensional event horizons, but in
the case of a four-dimensional universe, a
black hole would have a three-dimensional
event horizon. While this theory goes against
our intuition since we have no concept of
what a four-dimensional universe would look
like, it is actually firmly grounded in modern
mathematics describing space and time. The
problem, however, is that our understanding
of singularities is severely limited and we
will need to find a way to unify quantum theory
with General Relativity if we are ever to
find out what happened at the beginning of
time.
3. They slow down time
One of the most bizarre properties of black
holes is their ability to affect the passage
of time. According to the general theory of
relativity, gravity and acceleration are one
and the same, which means that the higher
the gravitational attraction, the slower time
flows. Due to their immense gravitational
pull, black holes warp the fabric of spacetime
to such an extent that time around it slows
down. However, this time dilation would only
be noticeable to stationary observers outside
the black hole’s gravitational field since
general relativity also states that time is
measured differently for the moving object
than the unmoving object.
Let’s say you could somehow approach the
event horizon of a black hole without being
stretched apart and killed by its crushing
gravity. If your friend was watching you from
a far-away spaceship, they would see you approach
the black hole, slow down, and eventually
come to a standstill and remain hovering outside
of the black hole forever. You, on the other
hand, wouldn’t notice that time was moving
differently. You would have no idea that thousands
of years are passing outside of the black
hole as you go over the event horizon and
approach the singularity where general relativity
breaks down and the laws of time and space
stop working.
2. They could erase your past
It’s widely accepted that no one could survive
a passage into a black hole. However, according
to researchers from the University of Berkley,
you may be able to enter certain types of
small black holes, but your past would be
erased and you would have an infinite number
of possible futures. Mathematical calculations
show that for some specific types of black
holes in an expanding Universe, it is possible
to survive the passage from a deterministic
world into a non-deterministic black hole.
Since spacetime is being increasingly pulled
apart, much of the distant universe will not
affect the black hole at all because that
energy can’t travel faster than the speed
of light. This means that the expansion of
the universe could counteract the time dilation
inside the black hole, and in certain cases,
cancel it entirely. These cases would have
to involve smooth non-rotating black holes
with a large electrical charge that would
allow an observer to survive passing through
the event horizon and into a non-deterministic
world. Even this theory is purely mathematical,
it certainly raises some interesting philosophical
questions. What would you do if you had the
chance to live out an infinite number of futures?
Leave your thoughts in the comment section
below!
1. They radiate light
You’ve probably heard many times that nothing
can escape from black holes - not even light.
But when it comes to black holes - things
are always more complicated than they seem.
According to quantum mechanics, when light
particles fall into a black hole, they are
split into two parts - matter and the antimatter.
These two particles can pop up right at the
event horizon so that one escapes while the
other one falls into black hole. This phenomenon
is known as “Hawking radiation” after
Stephen Hawking who first provided a theoretical
argument for the black hole radiation in 1974.
Since visible light is also part of electromagnetic
spectrum, a black hole that emits electromagnetic
radiation could be said to radiate light.
The problem with proving Hawking radiation
experimentally is that the entire black hole
would emit only a few hundred quantum particles
per second, which is much too small of a disturbance
to be observed at vast astronomical distances.
However, in 2014 a group of Canadian physicists
was able to successfully mimic Hawking radiation
in the lab. The black hole analogue was created
by trapping sound waves using an extremely
cold fluid. Physicists first chilled rubidium
atoms to less than 1-billionth of a degree
above absolute zero because at such temperatures,
the atoms behave as a single, fluid quantum
object and can be easily manipulated. They
then used laser light to manipulate the fluid
to flow faster than the speed of sound. At
this point, the sound waves travelling against
the direction of the fluid became trapped
and were observed popping in and out of existence
in a vacuum, mimicking Hawking radiation at
the event horizon.
What do you think is the strangest thing about
black holes? Leave your opinions in the comment
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