Imagine kicking a football towards the goal post. It takes off from the ground, zooms in toward the
target, but suddenly turns for a split second, as if it had hit an invisible object on its flight,
but then continues its original flight path and soars between the goalposts.
The audience erupts into loud cheers of celebration, but you can’t help but wonder:
What on earth was THAT!
This head-scratching physical phenomenon is just how dark matter behaves.
One of the greatest challenges that astral scientists and researchers face before they can
fully understand the universe is so-called "dark matter." Originally called the ‘missing matter’,
dark matter is the name given to particles that don’t absorb or emit light,
making them impossible to detect through observing electromagnetic radiation.
Think of it this way—how do you see or observe something in your everyday life?
You are able to see things because visible light, a type of electromagnetic radiation,
bounces off objects around you and then reaches your eyes.
All celestial bodies interact with electromagnetic radiation, including visible light, radio waves,
gamma rays, and the rest. More notably, they alter the way radiation travels around them,
which is how we detect far-off galaxies hiding billions upon billions of miles away.
But what if the object in question did not absorb, refract or reflect electromagnetic
radiation at all? How would you determine if an object was really there at all?
This essentially describes the biggest challenge in finding dark matter.
Since it does not emit or absorb electromagnetic radiation, it cannot be
detected or observed directly, in contrast to other celestial bodies in the universe.
Now, let’s go back to the football example we mentioned at the beginning of this video.
As the person who kicked the football, you know immediately that there must have been
something in its flight path that made it temporarily redirect and swerve.
Although you can't see anything, you know that something is in the way.
This is an oversimplified version of how the existence of dark matter
was initially proposed nearly 90 years ago.
In the early 1930s, famous Dutch astronomer Jan Oort examined star
motions in proximity to our central star—the sun. Since the galaxy wasn’t flying apart,
he postulated that there must be a large amount of ‘dark matter’—invisible
particles that cannot be detected directly or with the usual means of observation—that
was keeping the stars gravitationally bound to the galaxy’s center. He proposed that there was
three times as much dark matter as bright matter in the sun’s immediate neighborhood.
A Swiss astronomer, Fritz Zwicky, also proposed the existence of
‘some invisible matter’ around the same time.
Further clues to the existence of dark matter came later, when scientists examined the
glowing disks and halos that are present around galaxies. Astronomers also made
estimates about the distribution of dark matter by studying the inexplicable movement of stars.
This is how scientists explain the existence of dark matter: according to Newton's law of gravity,
stars orbiting the center of a galaxy should slow down the farther they are from the center.
However, look at the actual data of how stars spin in a galaxy.
You will find that there is no significant difference between the velocities of stars
near the galaxy’s center compared to those much farther away.
The most commonly accepted explanation for this
phenomenon is that huge spherical halos of dark matter surround visible matter
in galaxies. It is this dark matter that keeps galaxies gravitationally 'intact'.
Here’s an amazing fact: the matter that makes up all the known galaxies and stars only accounts for
5% of the universe's content! The vast majority of matter in the universe is actually dark matter!
So... how do we detect dark matter?
Astronomers detect and study dark matter by observing its effects on the visible celestial
bodies around it. Researchers believe that certain inexplicable movements of stars in galaxies
are caused by dark matter. Technology also plays a major role in assessing the
position of dark matter. Highly specialized computers help astronomers create models
to predict the behavior of galaxies, which further support the study of dark matter.
In recent decades, we have used artificial satellites to predict the
distribution of dark matter in a large group of galaxies and make detailed measurements.
Back in 1997, an image captured by the Hubble Space Telescope showed that the light from a
far-off galaxy was being bent by another unknown cluster in the image's foreground.
Astronomers predicted the foreground cluster's mass to be 250 times greater
than the mass of the visible matter present in the cluster. This helped them deduce that
the vast unexplained mass present in the foreground is composed of dark matter.
The Chandra X-ray Observatory has thus far made some detailed measurements
about how dark matter must be distributed across a large cluster of galaxies.
Since we don’t know much about dark matter, there are various hypotheses about its composition,
all of which have their strengths and weaknesses.
Some scientists believe that dark matter consists of regular space objects,
such as dark galaxies or cold gases. Others say that massive compact halo objects (aka
MACHOs), brown dwarfs or black holes make up the dark matter.
Real experimental data on the composition and existence of dark matter will help us determine
the shape and size of our universe and give us greater insight into its past and future.
Understanding dark matter will explain some of the
most mysterious phenomena we have observed in space,
and inform us as to how the universe has evolved in the billions of years since its inception.