Dark galaxy. Unlocking the mystery- What is Dark Matter?

Dark Matter and Dark Energy

Most of the galaxy is not
completely understood by human beings, with approximately only 5% visible or
“normal” matterXL1 . What is the other
95% made of?

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Visible/Normal matter includes
the billions of stars, galaxies, that is constructed of protons, neutrons and
electrons. OneXL2  of the most astonishing discoveries
of the 20th century is that the normal matter only forms 5% of the
galaxy. The rest of the galaxy consists of 27% dark matter and 68% dark energy.
(NASA,
2018) Thus, what is
“normal” matter is less than the “tip of the iceberg”.

Breakthrough observations

According to standard physics, stars at the boundaries
of a spinning, spiral galaxy should travel much slower than those near the
galactic center. A galaxy’s visible matter is most concentrated at the centre,
and due to gravitational force/energy is inversely proportional to distance,
the rotational speed should be smaller at further distances.  Contrary to this, in the 1950s astronomers observed
that stars orbit at approximately the same velocity, regardless of where they
are in the galactic disk. (National Geographic, 2018) This indicates that there is more matter than what could be seen.

Furthermore, if the only matter present
was visible matter, the cluster of galaxies would have collided into each other or would
have been flying around. By inspecting some planets or stars, their high
orbital velocity is unable to be supported solely by the gravitational force of
the visible matter. However, the stars, planets stay in place which again implies that there is more matter
than just visible matter. (NASA, 2018)

The observations above only makes sense if,
one assumes that the boundary stars are feeling the gravitational effects of an
unseen mass—”dark matter”—in a halo around the galaxy.

Unlocking the mystery-
What is Dark Matter?

Dark matter cannot be observed directly, it’s
an unseen force. It doesn’t interact with baryonic matter which is normal
matter. It’s completely invisible to light and other forms of electromagnetic
radiation, meaning that it does not reflect, absorb nor emit any type of
electromagnetic radiation. This makes dark matter impossible to detect with
current instruments. (Redd, N.T 2017) Dark
matter is also said to be “cold” because it is nonrelativistic
(slow-moving) during the “era of structure formation” or more commonly known as
the Big Bang. (Tate, K 2013,)

However,
scientists are positive that it exists because of the gravitational effects it
appears to have on galaxies. Dark matter has an important role in holding all
galaxies together. (National Geographic, 2018) To
hold the elements of the universe collectively, dark matter must make up
approximately 80 percent of all matter.  (Redd, N.T 2017)

Constituents of Dark Matter

So, what is dark matter made of?
Astronomers are still unsure of what dark matter is made of. However, scientists have a few
ideas for what dark matter might be.

Majority of all scientists think
that dark matter is composed of nonXL3 -baryonic
matterXL4 . One leading
hypothesis is that dark matter consists of exotic particles(not normal matter)
that don’t interact with normal matter or light but that still exert a
gravitational pull. Several scientific groups, e.g. CERN’s Large Hadron
Collider, are currently working to recreate dark matter particles for
study.(National Geographic, 2018)

The top candidateXL5  for such
an exotic particle is called “weakly interacting massive particles”
(WIMPS). WIMPS have a mass ten to a hundred times of a proton, but their weak
interactions with “normal” matter make them difficult to detect.

After the Big Bang, the universe
was so hot that particles were continuously created and destroyed. As the
universe expanded and cooled, these particles ceased to be created and
eventually the leftovers were eradicated, clearing the universe of exotic
states. A neutrino, which is a subtype of WIMP and a hypothetical particle,
however, will not be completely destroyed and the residue of these particles
will be left. (Berkley, 2007) A stable particle of mass 100 GeV (1.79 x 10-25 kg) interacting
with a neutrino via weak forces(the interaction between unstable subatomic
particles that causes radioactive decay) will leave just the right amount of
residue that corresponds to the density of dark matter.  (Redd, N.T 2017) This is
why neutralinos are the foremost candidate for dark matter.

Evidence for Dark Matter

Albert Einstein showed that massive objects in the universe twist and distort
light, allowing them to be used as lenses. By using gravitational lensing and analyzing
how light is “bent” by galaxy clusters, astronomers can create a map of dark matter in the universe. (Redd, N.T 2017)

 

An Expanding Universe

In 1929,
American astronomer Edwin Hubble studied supernovae (exploding stars) and determined that the
universe is expanding.  Scientists
postulated that gravity from dark matter that pulls all matter together would decelerate
the expansion of the cosmos- which is full of matter. (Redd, N.T 2013)

In the 1990s,
two independent teams of astrophysicists used the Hubble Space Telescope (HST) to examine the distant supernovae, in
order to calculate the deceleration. Surprisingly, they found that the
expansion of the universe wasn’t decelerating, it was accelerating! (National Geographic, 2018)

The universe has expanded at
various rates throughout history. Astronomers have discovered that during the
first half of the universe’s life, the expansion slowed down and after around 7
billion years ago, the expansion sped up. (NASA, 2018)

Scientists now think that the accelerated expansion of the universe is
driven by a kind of repulsive force generated by quantum fluctuations in
otherwise “empty” space. (National Geographic, 2018). The quantum fluctuations are a
“temporary change of energy in a point is space”. (Britannica, 2017) This
energy counteracts the gravitational force –  scientist called this “dark energy”.

Dark Energy

The concept of dark energy is even more mysterious than dark matter, and
its discovery in the 1990s was an utter shock to scientists.

Astronomers
can only detect it indirectly, by measuring the distance between galaxies, for
instance. (Perry, P2017)

Constituents of Dark Energy

Unalike dark matter, scientists have no credible explanation for dark
energy. Nevertheless,
scientists are confident dark energy exists because it causes the expansion of
the universe.

The leading theory considers dark energy as a property of
space. Research conducted by Albert Einstein indicates that dark energy is not
an empty space but is a space which has its own energy. In his
theory of general relativity, Einstein included a cosmological constant to account for the static
(not expanding or shrinking) universe scientists thought existed. This cosmological
constant was to keep the universe from collapsing in on itself. After Hubble
announced that the universe was expanding,(
Hubble, 2018) Einstein called
his constant his “biggest blunderXL6 .”(Olyer,
K 2014) Remarkably, Einstein’s blunder may be the best fit for dark energy. This energy which is a property
of space itself, does not diminish when it causes the universe to expand. As a
matter of fact, as the universe expands, more dark energy is generated in the
space, which as a result will cause the universe to expand at an increasing
rate. (Redd, N.T 2013)

Australian and
U.S. astrophysicists won the Nobel Prize in physics in 2011, for their 1998
discovery of the Hubble Constant. This is the rate at which the universe
expands. (Perry, P2017)

However, the reason why the
cosmological constant matches up with observations still leaves scientists bewildered.

Another idea proposed is that dark energy is a fifthXL7  and unknown type of fundamental force
called “quintessence”, which fills the universe like a fluid. There
are four fundamental forces of nature which are eternally at work. These
include the commonly known ones that are on a universe scale such as gravity
and electromagnetism. (Hyperphysics, 2018) There are also the microcosmic
forces the strong and weak atomic forces. The strong forces are the force which
holds a nucleus together, the weak force governs the unstable subatomic
particles to decay. (National Geographic, 2018) Cosmologists suggest that “quintessence” is an exotic type
of energy field that pushes particles away from each other, overpowering
gravity and other fundamental forces.

Alternatively, scientists may
have not correctly understood how gravity works. The current theory of General Relativity
by Einstein is

Overall Comparison between Dark Energy and Dark
Matter

Like dark
energy, dark matter continues to puzzle scientists. Scientist predict that both dark
energy and dark matter were forged in the big bang theory. Dark energy is a
force that attributes to the expanding universe, and dark matter explains how
the cosmos stays together. Dark energy repels the gravitational force (dark
matter). Dark energy causes the universe to expand faster. The particles which
the dark matter and dark energy is made up of is still uncertain.

Does Dark Energy and Dark
Matter actually exist?

André Maeder,
honorary professor in the Department of Astronomy at the University of Geneva
(UNIGE), has a radical theory that may change the direction of astrophysics. He
postulates that dark matter nor dark energy exist. These concepts he
believes are
no longer required. The hypothesis
revolves around scale invariance. “Scale
invariance is when the properties of something do not change no matter how you
measure it, regardless of scale.” We can multiply their energies or lengths by any
number and they do not change. Their properties don’t change. The same is true
of empty space. Whether you zoom in and out, it’s the same. (Perry, P
2017)

Maeder
proposes that instead of dark matter or dark energy, scientists have simply
forgotten to include scale invariance into the Standard Model—our current model
of the universe. (Gary, S2017)

Conclusion

The cosmos consists mostly of dark energy, which explains why
the universe is increasing its expansion. Dark matter is a competing force to
dark energy which makes up 27% of the ingredients to the galaxy. The “normal
matter” which only contributes to 5% of the whole galaxy is not actually that
“normal”. Dark energy and dark matter
emphasizes on our lack of knowledge of the galaxy that we still have a great
deal to learn. Future research
might include determining the constituents of these mystical concepts or even
disproving these hypothesis with more advanced technology. Any discovery could be an important step in
determining the ultimate fate of the universe.

 

 

 

 XL1

 XL2Define
normal or visible matter? What classify them as normal?

 XL3

 XL4

 XL5A
suggestion of what it could be or close to be is WIMPS which is a exotic
particle

 XL6because

 XL7explain
fundamental force