For hundreds of years, physicists have hypothesized
that the Universe should contain black holes.
If enough matter is gathered into a small
enough volume of space, the gravitational
pull will be so strong that nothing can escape.
Not even a light.
They are predicted by both Newton's and Einstein's
theories of gravity.
Nothing is stranger than a black hole.
A black hole forms when a massive, dying star
crumples under its own gravity.
It shrinks until all of its mass is contained
in an infinitely dense point, called a singularity.
Its gravity is so intense, not even light
can escape.
On April 10, 2019, the Event Horizon Telescope
collaboration releaseD their first-ever image
of a black hole.
Here's what we know so far...
Black holes are an inevitable consequence,
at least in theory, of having a speed limit
in your Universe.
The greater your motion through space, the
lesser your motion through time, and vice
versa.
Astrophysically, black holes are surprisingly
easy to create.
Within our Milky Way galaxy alone, there are
likely hundreds of millions of black holes.
We believe there are three mechanisms capable
of forming them, although there may be more.
The first mechanism is with the death of a
massive star.
Where the core of a star much heavier than
our Sun, rich in heavy elements, collapses
under its own gravity.
When there's insufficient outward pressure
to counteract the inward gravitational force,
the core implodes.
The resulting supernova explosion leads to
a central black hole.
The second mechanism is with the direct collapse
of a large amount of matter.
If enough matter is present in a single location
in space, it can generate a black hole directly,
without a supernova or similar cataclysm to
trigger its creation.
The third mechanism is with a collision of
two neutrons stars.
They are the most dense, massive objects which
do not become black holes.
Add enough mass onto one and a black hole
can arise.
A little more than 0.1% of the stars that
have ever been formed in the Universe will
eventually become black holes in one of these
fashions.
Some of these black holes will be only a few
times the mass of our Sun; others can be hundreds
or even thousands of times as massive.
But the more massive ones will do what all
extremely massive objects do when they move
through the gravitational collection of masses.
They will sink to the center, through the
astronomical process of mass segregation.
Additionally, black holes don't exist in isolation,
but in the messy environment of space itself,
which is filled with matter of various types.
When matter gets close to a black hole, there
will be tidal forces on it.
The part of any object that happens to be
closer to the black hole experiences a larger
gravitational force than the part farther
away from the black hole, while the portions
that bulge on any of the sides will feel a
pinch towards the center of the object.
All told, this results in a set of stretching
forces in one direction and compressing forces
along the perpendicular directions, causing
the infalling object to "spaghettify."
The object will be torn apart into its constituent
particles.
Owing to a number of physical properties and
dynamics at play, this will cause matter to
accrue around the black hole in a disk-like
shape: an accretion disk.
These particles making up the disk are charged,
and move in orbit around the black hole.
When charged particles move, they create magnetic
fields, and magnetic fields in turn accelerate
charged particles.
This should result in a number of observable
phenomena, including:
- emitted photons from throughout the electromagnetic
spectrum, particularly in the radio.
- flares that show up at higher energies arising
from when matter falls into the black hole.
- and jets of both matter and antimatter that
get accelerated perpendicular to the accretion
disk itself.
All of these phenemona have been seen for
black holes of various masses and orientations,
further giving credence to their existence.
Going into the Event Horizon Telescope's big
reveal, we get the first image of a black
hole.
The image reveals the black hole at the center
of Messier 87, a massive galaxy in the nearby
Virgo galaxy cluster.
This black hole resides 55 million light-years
from Earth and has a mass 6.5-billion times
that of the Sun.
How did the Event Horizon Telescope take the
black hole picture?
Black holes are extraordinary but they are
impossible to look at directly and are impossible
to take photographs of.
The incredible black hole was photographed
55 million light-years away from Earth in
the galaxy Messier 87.
Astronomers on Earth linked eight powerful
radio telescopes to snap what is essentially
the shadow of the black hole, cast by the
glowing clouds of gas around it.
For hundreds of years, humanity has expected
black holes to exist.
Over the course of all of our lifetimes, we've
collected an entire suite of evidence that
points to their existence.
