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Dark Matter and Dark Energy: Mysteries of the Universe

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 Original Article

Nirakar et al. 2017 ISSN: 2349 - 4891

ISSN: 2349 – 4891

International
Journal of Recent Research and Applied Studies
(Multidisciplinary Open Access Refereed e-Journal)

Correlations of Biomechanical Characteristics with Ball Speed in Penalty Corner Push-In

Dark Matter and Dark Energy: Mysteries of the Universe
Nirakar Sapkota1 & Binod Adhikari1, 2
1
Department of Physics, St. Xavier’s College, Maitighar, Kathmandu, Nepal.
2
Department of Physics, Patan Multiple College, Patandhoka, Lalitpur, Nepal.

Received 15th May 2017, Accepted 1st July 2017

Abstract
The Universe has a flat geometry and its density is very close to critical density. However, the observed amount of
matter accounts for only 5% of the critical density. The rest of the 95% is completely unknown to us which exists in the
form of Dark Energy (68%) and Dark Matter (27%). We present an overview of how the very idea of the existence of Dark
Matter emerged and some compelling evidences for the existence of such matter. Moreover, we also provide an insight on
how scientific ideas have evolved from a static Universe to an expanding Universe and then to an accelerating Universe. In
addition, we explain fundamental concepts related to Dark Energy and discuss briefly on the evidences of Dark Energy. We
also discuss some alternative solutions to the problems of Dark Matter and Dark Energy provided by different scientists.

Keywords: Dark Matter, Dark Energy, Bullet Cluster, Quintessence.

© Copy Right, IJRRAS, 2017. All Rights Reserved.

1.Introduction of the Universe which governed its fate. The

In the 1930s, one of the first indications of Cosmological Constant can represent Dark Energy which
“missing mass” appeared when Fritz Zwicky observed will be explored in a much detailed way in this project.
the Coma Cluster and discovered that the galaxies within Dark Energy rules the Universe in the sense that
the cluster were moving with velocities much higher than it comprises of about 68% of the total energy-mass
what the collective gravity of all galaxies in the cluster density of the Universe. The very existence of this
would allow. They should have all scattered around by Energy serves to flatten the curvature of the space and
the centrifugal force being much greater than the gravity also causes the expansion of the Universe to accelerate.
which was calculated from masses of individual galaxy. Until the late 1990s, scientists still hoped to find out
He said that there must be some “missing mass” within whether the Universe will continue to expand forever at
the cluster whose extra gravity caused such observations. a decelerated pace or will eventually reach a point when
Many other observations on different clusters and gravity will win over- making the Universe contract
galaxies later lead to similar conclusions by different towards a big crunch. However, the Universe was found
scientists. The name to the source of such gravity was to be accelerating in its expansion. (Riess, 1998;
given “Dark Matter”. It accounts for about 85% of the Perlmutter, 1999).
mass in the Universe.
Friedmann’s equations suggested that the 2.1. Dark Matter
Universe had to be either expanding or contracting. It By tracing the absorption and emission of light,
couldn’t be stable according to the equations. Einstein we can trace the matter present in the Universe. In fact,
couldn’t cope up with the very idea of expansion of there are various types of astronomical bodies with
space itself. Thus, he added a term called Cosmological varying efficiency. Some are extremely luminous
Constant in his equations to make the Universe static. (Supernovae explosions) whereas others are very dim
(Straumann, 2002) Later, Edwin Hubble (1929) gave the (planetary bodies) with a low light emission per unit
best dataset supporting that the Universe is expanding. mass. The extent to which an object is effective in its
Einstein immediately removed the Cosmological emissivity can be described by the mass-to-light ratio of
Constant from his equation and said that adding the the object (M/L). However, all astronomical objects do
Cosmological Constant was his “Biggest Blunder”. not necessarily emit or absorb light.
However, much later have we realized that his “Greatest Experimentally, it is found that total mass
Blunder” was in fact one of the fundamental properties calculated using the motion of objects exceeded the
estimated luminous masses of different astronomical
Correspondence objects by a large fraction. The matter responsible for
Nirakar Sapkota such phenomenon is what we call “Dark Matter”. In fact,
E-mail: sapkotanirakar07@gmail.com, Ph. +9199986 88613 the term “Dark Matter” was coined by Jacobus Kapteyn
in 1922 in his studies of stellar velocities. He suggested

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that no dark matter is needed in the solar neighborhood. He was surprised to find that the orbital velocities were
Jan Oort(1932) carried out dynamical study of the Milky almost a factor of ten larger than the mass calculated
Way Galaxy. He discovered that vertical motion of stars from optical observations allowed.
near the Galactic Plane was at an alarmingly fast rate In spiral galaxies, visible matter consists of stars
than that was possible considering the density due to and interstellar gas which rotate around the galactic
known stars. This suggested the existence of some center on nearly circular orbits. Most of the observable
unseen matter. He said Dark Matter is twice as much as matter is found to be in a thin disc. Galaxy-rotation
normal matter. This was later found to be wrong. curves suggest that velocity remains constant or
However, Fritz Zwicky (1933 A.D.) observed the Coma increases after about 5 kpc Matts Roos, 2010) which is
Cluster and claimed the existence of Dark Matter. Thus, far from the expected model as shown in Fig.1
the discovery of Dark Matter is credited to Fritz Zwicky.

Figure I
Rotation curve of spiral galaxy M33 (yellow and blue points) and white line indicates the predicted one from visible matter
observations. Only by adding a dark matter halo around the galaxy, the discrepancy between the curves can be accounted
for. (Source: Corbelli and Salucci, 2000)

Mass-to-light ratio (M/L) of all the stars in baryonic density cannot exceed 0.05 times the critical
galaxies cannot explain all the mass in the Universe density. However, constraints from CMB, supernovae
.Clearly, it suggests that matter which doesn’t emit observations and galaxy redshift surveys suggest that
radiation is present in the galaxies. Moreover, in some matter density should be about 0.27 times the critical
elliptical galaxies, strong gravitational lensing shows density of the Universe. So, the remaining 0.22 of the
evidence for dark matter. (Bertone, 2004). There are two critical density has to be that of non-baryonic matter.
types of Dark Matter : Baryonic Dark Matter (BDM) and This is why matter was separated as baryonic and non-
Non-Baryonic Dark Matter. True nature of both of these baryonic matter. (Gondolo, 2004)
dark matters aren’t yet known. This is called “The Dark Cold molecular clouds and brown dwarfs are
Matter Problem”. However, “dark matter” in general is candidates for dark matter in the galaxies. According to
used to refer to the non-baryonic dark matter. some observations, MACHOs provide a significant
quantity of halo dark matter. However, statistics of
2.1.1. Baryonic Dark Matter microlensing events is too low to make strong
Cosmic Microwave Background (CMB) tells us conclusions. How MACHOs formed is one problem
how the Universe was before the development of whereas what the rest of Dark Matter in the galaxies is
structures and at the time of decoupling of photons from made up of is another. Observation of near-infrared and
baryons i.e. about 380,000 years after the beginning of faint optical emission of halo around the galaxy
time. (Hu & Dodelson, 2002) Using CMB, the baryonic NGC5907 suggest that there is expected distribution of
density were measured which along with conditions gravitational mass- providing the first direct indication
required for primordial nucleosynthesis suggest that the about very faint stars (with mass about 0.1 solar masses)

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being responsible for most effects of dark matter in the The acceleration of gravity in MOND (a) is related to
galactic halos. (Jetzer, 1996) that in Newtonian dynamics (aN) by
aN= aμ(a/a0)
2.1.2. Non-Baryonic Dark Matter where a0 is one Angstroem per second per second and
Based on velocities of particles of which the regarded a new constant of Physics.
Non-Baryonic Dark Matter is made up of, it is divided In the outer regions of the galaxies, acceleration
into three types: hot dark matter (HDM), warm dark is many orders of magnitude smaller than what we have
matter (WDM) and cold dark matter (CDM). At the time otherwise predicted. This is explained by MOND by
of formation of galaxies, HDM was relativistic which assuming that when acceleration is low compared to a0.
affected the formation of smallest objects. CDM was 𝐺𝑀𝑎 0
For a<<ao, 𝑎 = 𝑎𝑁 𝑎0 = , where M is the
non-relativistic and collapsed under the effect of its own 𝑟
gravity. WDM was semi-relativistic and can be mass generating gravitational field.
considered as an intermediate between CDM and HDM. The velocities of stars in galaxies would be
(Gondolo, 2004) Examples of HDM: light neutrino; of more than expected from Newtonian gravity if the
CDM: Neutralinos, WIMPZILLAs, axions, and of gravitational force was directly proportional to the
WDM: keV-mass sterile neutrinos and gravitinos. square of centripetal force (instead of centripetal force
Another way of classifying Non-Baryonic Dark alone) on the galactic scales or if the force of gravity
Matter is Type Ia (that are known to exist), Type Ib (that varied inversely with radius (Milgrom, 2002) From the
are yet not discovered but can solve genuine physics above equation, it is also seen that acceleration is
particle problems and are interact and possess mass inversely proportional to radius (and not with radius
within well-defined particle model) and Type II (that squared). So, the galactic rotation curves can be
aren’t as strong candidates as the other two). However, explained. Thus, there is no need of dark matter to
with more understanding of associated Physics and explain flat rotation curves in galaxies. (Milgrom, 2002)
nature of particle, a particle can move from Type II to MOND can correctly predict the flat rotation
Type Ib and finally to Type Ia with its discovery curves of galaxies beyond a certain distance. Moreover,
(Gondolo, 2004). mass discrepancy plotted against typical acceleration in
galactic systems gives similar pattern as per MOND’s
2.1.3. Modified Newtonian Dynamics (MOND) predictions. However, every galaxy can be an
When acceleration of gravity becomes less than independent test of MOND, regarding whether or not the
a fixed value, mass discrepancies are seen in the stellar rotation curve is flat. (Scarpa, 2006) When we try to fit
systems. Realizing this, MOND was proposed by M. the rotation curves, a0 is an inflexible constant- the
Milgrom to behave as alternative approach to explain the online flexible parameter being the mass-to-light ratio
effects of non-baryonic dark matter. (Scarpa, 2006) It is (associated with the M term) and somewhat flexibility is
a non-relativistic concept applicable on galactic scales to observed with the distance r. Thus, MOND has very less
match with the observations of galactic-rotation curves flexibility than a dark-matter model which can explain
which would otherwise need dark matter. any kind of rotation curves. (Scarpa, 2006).

Figure II
Rotation curve of galaxies along with data. Yellow lines represent the curves predicted by MOND and the red lines
represent the curves predicted by Newtonian dynamics. (Source: Mordehai Milgrom,2002)

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2.1.4. Bullet Cluster lensing. (Bradac et al. 2006, 2009) Lensing mass
Bullet Cluster consists of two colliding clusters distribution was studied to provide a powerful evidence
of galaxies at z=0.296 (Paraficz et al., 2016). In this for the existence of dark matter which challenges
system, ssub-cluster “Bullet” has undergone collision theories of modified gravity like MOND and TeVeS
with the main cluster, nearly at the plane of sky (Barrena (Milgrom 1983; Bekenstein, 2004) It was found that the
et al. 2002). As a result of collision, strong bow shock majority of mass component exists in spatial agreement
has been produced in the intra-cluster gas- stripping not with the X-ray gas but with the galaxies. This verifies
away the gas from the cluster potential. (Markevitch et that dark matter doesn’t collide with anything. (Paraficz
al., 2002). Since the gas and galaxies have some offset, et al., 2016). However, the separation of dark matter and
there is a possibility to indirectly measure the luminous matter could very well be a projection effect in
distribution of total mass by the use of gravitational MOND. (Angus et al. 2006)

Figure III
Bullet Cluster: Blue region indicates source of gravity whereas the red region indicates the gas clouds in X-rays. Clearly,
most of the gravity is not from the region of baryonic matter.[Source: Markevitch et al., 2004]

2.1.5. N-Body Simulations distributed 3 to 10 times the total mass points they had
Ostriker and Peeble presented a theoretical put. This suggested a clear need of dark matter.
argument for the requirement of massive dark matter
halos to stabilize the disks of spiral galaxies. (Frenk, 2.1.6. Evidences from Andromeda Galaxy
2012) By using N-body simulations, 300 mass points The motion of stars of the Andromeda Galaxy
were programmed in computer which represented groups was studied using sensitive photon detectors. (Rubin,
of stars in a galaxy rotating about central point. They had 1970). The hydrogen gas cloud outside the visible edge
simulated the galaxy such that there were more mass of Andromeda was expected to move slower than gas at
points (stars) near the center and fewer towards the edge. the galaxy’s edge. However, it was found that the orbital
The simulation was based on calculation of gravitational speed of hydrogen clouds remain constant outside the
force between each pair using Newton’s formula and visible galactic edge. This suggested the need of dark
then showing how the stars would move in a short period matter whose quantity increased with increasing distance
of time. They were able to track the motion of the stars from the center of the galaxy.
(mass points) over a long period by repeating the
calculations for many times. They discovered that even 2.1.7. Evidences from lensing of Quasars
shorter than an orbital period, most of the stars (mass Quasars are distant objects which are about 100
points) had to collapse to a bar shape near the galactic times more luminous than an entire galaxy. Images of
center according to the calculations; which isn’t what we quasars which are far away are lensed by the galaxies
see. Thus, they concluded that for the system to be stable between us and the quasar. The observations of such
(like we observe), the mass has to be uniformly lensing can provide significant insight about how dark

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matter is distributed. Several images of the same quasar brightness of the images can be used to trace out where
appear due to gravitational lensing when we view them the dark matter is present and how much dark matter is
through our telescopes. By measuring the brightness of there. Observations from such lenses have concluded that
each image of the quasar, we can determine how matter dark matter clumps in galaxies should not be larger than
in the galaxy in between is distributed. Normal matter 3000 light years.
can be located by using optical measurements. Then, the

Figure IV
Gravitational lensing producing several images of distant quasar.(Source: The European Space Agency’s Faint Object
Camera on board NASA’s Hubble Space Telescope, 1990)

2.1.8. Dark Matter in the Milky Way relativistic particles which were produced by falling out
The MACHO Project (1992) was designed to of thermal equilibrium with the hot and dense plasma in
look for dark matter in the form of MACHO in the the early Universe. Any dark matter candidate particle
galactic halo of Milky Way. (Alcock, 1995). It was based which can interact with the particles of the Standard
on observing gravitational lensing. “Large Magellanic Model via force with strength similar to weak nuclear
Cloud” is a small satellite galaxy that revolves around force is referred to as WIMP. When the early Universe
the Milky Way and the MACHO project was based on was at high temperature, thermal equilibrium was
monitoring the light from stars in that galaxy which will established and number density of photons and WIMPS
be gravitationally lensed if a MACHO passes in front of were roughly same. Due to the cooling of the Universe,
them. An automated telescope at Australia’s Mount both of their density decreased. After the temperature
Stromlo Observatory was used in the project to observe reached below the mass of WIMP, the formation of
such transit. However, no significant change to account WIMP became rare whereas the annihilation didn’t stop
for dark matter was observed. Another project was but proceeded. The number density of WIMP’s
“EROS” was run by European Organization for decreased at an exponential rate. However, the
Astronomical Research which also got similar negative equilibrium was disturbed at some point when the
result. Observations of about 7 million stars lead to only density of WIMP significantly dropped-making the
one possible MACHO transit which was much less than probability of two WIMPs annihilating very low. The
what theory predicts (42 events are predicted by theory). number of WIMPs didn’t drop anymore. Predicted relic
Moreover, SuperMACHO survey succeeded the density of WIMPs at present is inversely proportional to
MACHO Project and it was concluded that the the strength of interaction. If the relic density is to be
MACHOs can’t simply account for the observed density equal to that of dark matter density, the strength of
of dark matter in the Milky Way. interaction is expected to be equal to electroweak-scale
interactions. So, a stable particle which annihilates with
2.1.9. WIMPS (Weakly Interacting Massive Particles) electroweak-scale cross section can behave as what we
They are non-Standard Model and non- call “dark matter” in the Universe. (Griest, 2006)

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2.1.10. Supersymmetry: still wasn’t enough energy-mass density to account for

Supersymmetry (SUSY) is a hypothetical the density which would cause the Universe to have flat
proposed symmetry which relates elementary particles geometry (i.e. critical density). Then, something called
bosons and fermions. If this phenomenon exists, every “Dark Energy” was brought into theories which has a
known particle must have its supersymmetric negative pressure. It turns out that in the playground of
counterpart. Certain supersymmetric particles are gravity of matter and negative pressure effects of Dark
predicted to have same quantum numbers which is why Energy, the latter is much stronger; thus causing the
they can mix and produce particles which are not exact Universe to expand at an accelerated rate.
partners of any particle described by Standard Model. Albert Einstein added a term called
For instance, the Higgsino, photinos and Z-ino mix into Cosmological Constant to his equations because he
random combinations called Neutralinos (Griest, 2006). couldn’t cope up with the fact that Universe which is
Light supersymmetric particle (LSP) is a everything could actually expand or contract. He did so
remarkable dark matter candidate as it is stable and also to make the Universe static. He said, “In order to arrive
because supersymmetric particles interact through at this consistent view, we admittedly had to introduce an
electroweak-strength interactions. Neutralino is LSP extension of the field equations of gravitation which is
which is why WIMP dark matter investigators focus on not justified by our actual knowledge of gravitation. It
detecting it. In fact, the detection of any of the predicted has to be emphasized, however, that a positive curvature
supersymmetric partner can confirm the existence of all of space is given by our results, even if the
supersymmetric particles (Griest, 2006). supplementary term is not introduced. That term is
necessary only for the purpose of making possible a
2.1.11. Dark Matter and Structure formation: quasi-static distribution of matter, as required by the fact
According to the Standard theory of cosmic of the small velocities of the stars.” (Straumann, 2002)
structure formation, early Universe was nearly perfect in As per our current understandings, the
its homogeneity except few tiny density modulations. cosmological constant acts against gravity and wins over
These modulations were later enhanced due to the gravity to cause accelerated expansion. So, even though
influence of gravity which lead to the formation of Einstein had added this term with negative pressure to
galaxies, clusters, and large scale structures we see in the merely balance out gravity and not allow the Universe to
Universe. Primordial density variations are believed to collapse, it turns out that something very similar to
have occurred due to certain quantum fluctuations in the Cosmological Constant is required to explain the
very early Universe which were magnified to acceleration of Universe in its expansion.
macroscopic levels when Cosmic Inflation took place.
Several experiments have determined the amplitude of 2.2.1. The Expanding Universe
density fluctuations at the period when the CMB Distances are the hardest things to measure in
radiation was released. It was found that the amplitude of astronomy. Simply by observing the brightness of an
fluctuations is not enough to allow the observed object in the sky, we cannot tell if it is a large luminous
structures to form with the mere presence of baryons and body billions of light years away or a small body with
radiation. WIMPS or dark matter particles are essential less luminosity just a couple of million light years far.
since they are not affected by photon pressure. This For the same reason, standard candles are significant in
serves to create a strong argument against baryonic dark Astronomy. These are objects whose luminosities are
matter. (Griest, 2006). known to us and no matter how far they are, their
distance can be worked out with the help of observed
2.2. Dark Energy flux and their actual luminosity we know. One of such
Science makes all its admirers wonder about the standard candles are Cepheid variables which have their
mysteries of the Universe and scratch their head trying to brightness increase and decrease periodically. It turns out
explain the phenomena we observe. By the late 1800s, that the longer the period, the brighter the Cepheid
the advancements in Classical Physics had made some variables. This was figured out for the first time by
physicists believe that there weren’t much things to Henrietta Leavitt in 1912. Thus, no matter how far a
explore about Physics. People thought there would be no Cepheid variable is, we can work out its true luminosity
more scientific breakthroughs. There were just few with the help of period of brightness change and then by
experiments which had to be done with better precision; measuring the flux with telescope, we can work out how
however, the then existing concepts were thought to be far away it is using the following relation.
able to explain all the phenomena in the Universe. In 𝐿
𝐹= 2 ; where L = Luminosity, F= Flux, D= Distance.
4𝜋𝐷
contrast, the scientific revolution in the 1900s brought
tons of new ideas in Physics and mysteries were
Harlow Shapley measured the size of our
introduced one after another which brought human
galaxy using Cepheid variables as standard candles.
consciousness back to an ideal thought essential for
deSitter (1917) was among the first to consider galactic
scientific researches- “The more we discover, the more
velocities in a cosmological context and Carl Wirtz
mysteries arise.”
(1922) was the first one to detect the distance-velocity
Even with dark matter and normal matter, there
relationship. He proposed redshift as an effect of time-

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dilation. (Wirtz, 1924) In 1927, Lemaitre published his way, for over a decade. However, Edwin Hubble is often
paper proposing that the Universe is expanding. mistaken to be the first one to discover the redshifts of
However, his work didn’t draw much attention and galaxies. Edwin Hubble (1929) combined the distances
Einstein told him “Your calculations are correct, but your he had measured using Cepheid variables with velocities
physical insight is abominable.” (R Smith, 1990). The of galaxies calculated from their redshift. He plotted a
astronomers at that time had attempted to determine any graph against velocity and distance reaching a
observational form of redshift-distance relation. conclusion that further galaxies were moving away from
However, all of their evidence was not convincing as us at a faster rate. Hubble and Humason (1931) measured
their plots of radial velocity against distance looked more 40 new radial velocities and plotted them against
like scatter diagrams. (Smith, 1990) distance to obtain a better result showing velocity-
The light from galaxies is stretched out by distance relationship (Bergh, 2011). However, the reason
expansion of the Universe which is known as redshift. for the observed redshift of galaxies was unclear at that
Vesto Melvin Slipher had accumulated several time.
measurements of velocities of galaxies determined this

Figure V
Velocity-distance graph plotted by Edwin Hubble in 1929.(Source: E. Hubble, 1929)

Figure VI
Velocity-distance graph plotted by Edwin Hubble and Humason in 1931 [Source: Hubble andHumason, 1931]

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The “apparent recession velocities” is the result 2.2.2. First Indication of Dark Energy
of increase in proper distance due to the expansion of Astronomers were keen to determine the
space itself in between the galaxies. This happens only deceleration rate of the Universe which would appear as
between systems which aren’t held together by gravity. small yet real departure from Hubble’s Law if Hubble
Thus, this effect isn’t seen within the galaxies of the diagram was extended to very large distances. However,
Local Cluster which are bound by their mutual gravity. It the telescopes we have cannot afford to see the light
is significant to note that cosmological redshifts are not from stars which are billions of light years away. For the
Doppler shifts of galaxies flying away from us. Except same reason, astronomers based their observations on
for motions within galaxy clusters, galaxies are at rest type Ia Supernovae which are standard candles in
and it is the space between them which is expanding. Astronomy. There are, however, several challenges
Due to the expansion of the space, any photon which associated with determining the cosmic deceleration or
passes through the space is stretched i.e. its wavelength acceleration by the help of these supernovae. These
increases. Since the photons from distant galaxies spend events are rare as they take place about once every
more time travelling through expanding space, they are hundred years in a typical galaxy. This means searching
more stretched than the photons from galaxies which are about 10,000 galaxies would allow us to find two of
nearby. This is why redshift increases with increase in these events a week which definitely is not possible for
distance. However, it is to be noted that the red-shift humans. Moreover, unlike Cepheid variables,
distance relation is different from the recessional supernovae don’t have direct brightness-vibration period
velocity-distance relation (which is linear) observed by relation.
Edwin Hubble. However, extra-bright type Ia SN increases to
A negative pressure field (similar to Dark its peak luminosity and decreases slowly compared to its
Energy as we think of it now) must have driven the dimmer counterpart. This is why the study of light curve
inflation of the Universe in its very early stage. (Guth, (graph of luminosity as a function of time) of SN is
1981) Inflation is a phenomenon which eases the horizon significant to determine their luminosity. Such use of
problem and the flatness problem of the Friedmann Phillips relationship i.e. the relation between rate of
Cosmology (referred to as Big Bang Cosmology). luminosity evolution after maximum and the peak
Horizon problem is related to the homogeneity observed luminosity for a Type Ia supernovae can help to measure
in the distant points in CMB whereas the flatness distances to about 7% accuracy. Since the uncertainty in
problem is related to the precision in flatness of the average value we measure becomes smaller as the square
Universe in its early age. Cosmic Inflation lasted from root of the total number of times the measurement is
10−36 seconds to about 10−33 seconds after the Big Bang. repeated, measurements of more of these events are
It is currently thought that Inflation must have occurred required for experimental accuracy which is yet another
at a much higher energy density compared to the density challenge. Another way to use them as standard candles
of dark energy we observe today. However, the relation is to exploit the fact that they explode with the same
of inflation and dark energy aren’t yet clear which is why Chandrasekhar mass (about 1.4 solar masses), so their
the Cosmological Constant was thought to not related to luminosity is known to us. By observing the flux, the
the Universe’s faith, back then in 1980s. distance to these events can be worked out by the flux-
luminosity relation mentioned in section 2.2.1.

Figure VII
Light curves of SN 2007le (Source: KAIT and Lick Nickel 1 m data)

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By the end of the 20th century, two separate the Universe was expanding slower in the past which is
group of astronomers were ready with their results from why it took longer for its light to reach us. However, it
observations of type Ia supernovae. In 1998, the High-Z accelerated in its expansion and reached the current rate
Supernova Team measured 16 distant and 34 nearby of expansion. In 1999, the Supernova Cosmology Project
supernovae and were startled to see that the Universe with even a larger sample of 42 distant supernovae
was accelerating in its expansion (Riess, 1998). The published its results which agreed with that of High-Z
distant supernovae were about 25 percent dimmer for a Supernova Team ( Perlmutter, 1999).
given redshift than expected which clearly indicated that

Figure VIII
Observed magnitude against redshift plotted for highly redshirted as well as near type Ia Supernovae [Source: Perlmutter,
2003].
Later, astronomers continued to look for even 2.2.3. Brief Discussion of Evidences of Dark Energy
more distant type Ia supernovae (about 12 billion light If the mass density of the Universe dominated
years away) and found that the most distant supernovae the cosmos, it would eventually decelerate the expansion
are actually too bright than expected. This further reveals of the Universe. In that scenario, the Universe would
that when the Universe was young, galaxies were closer have a higher rate of expansion in the past than in the
which caused their gravitational pull to be much present. So, the light from the Supernovae would have
effective than the effect of dark energy. So, the faced higher stretching earlier when they were emitted
expansion was slowed down. But as Universe continued compared to the present. The redshift we would predict
its expansion, the distance between the galaxies for a given brightness of supernovae would thus be less
increased which caused their gravitational pull to than the actual redshift observed. This means for a given
become weaker compared to dark energy; thus leading to redshift, supernovae would appear brighter than
acceleration. This happened about 6 billion years ago. expected.
(Michael Seeds and Dana Backman, 2012) In contrast, since the supernovae are fainter for
In short, observations of supernovae in the region where a given redshift than expected, we can conclude that
acceleration had just started appear dimmer than mass density doesn’t alone dominate the Universe. In
expected but the supernovae even farther, belonging to fact, adding cosmological constant helps us to fit the
the time when the Universe was decelerating in its initial supernovae data quite well. Perlmutter and Goobar
phase are brighter than expected. The speculations about (1995)had found that by observing type Ia Supernovae
the initial deceleration and later acceleration are made data for a wide range of distances, it is possible to
after these observations. determine the effects of mass density and vacuum-energy
density. The supernovae data of 1998 implies that
vacuum energy density is larger than the mass density

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Nirakar et al. 2017 ISSN: 2349 – 4891

(Perlmutter, 2003). This is why the Universe is some “fine tuning” (Perlmutter, 2003). Since the
accelerating in its expansion. If the Universe really has a considerations of this constant vacuum energy density
flat geometry as indicated by measurements of CMB, represented by Cosmological Constant as the
70% of the total energy density is vacuum energy and accelerating energy (dark energy) has these problems,
30% is mass. some physicists have proposed a dynamic scalar-field to
Baryonic Acoustic Oscillations (BAO) provide be responsible for the effects of “dark energy”.
another significant evidence for the existence of Dark
Energy. BAOs are periodic fluctuations observed in 2.2.4. Could there be something wrong with our
density of baryonic matter that is visible in the Universe. interpretation of Dark Energy?
Just as the Supernovae act as standard candles, BAOs act Astrophysicists often love to argue about
as “standard-ruler” to measure length scale in different possibilities and to broaden their horizon about
cosmology. From the observations of different large scale the possible explanations of data obtained from
structures in the Universe by the use of different surveys, experiments. There could be some interpretation of the
length of the standard ruler is measured to be about data without requiring the need for Dark Energy, one of
490million light years in the present context. (Eisenstein them being the argument supporting “Luminosity
et al., 2005) In the primordial plasma of the Universe, Evolution”.(W. Li, 2003) However, we haven’t fully
matter had gravitational force as well as photon-matter understood whether or not they evolve at different
pressure which acted in opposite directions i.e. redshifts. Another scenario can also explain the results
gravitational force attracted matter and the photon-matter without considering the need for Dark Energy (Clifton,
pressure created outward force. This resulted in 2009). Assume that the Universe is inhomogeneous, the
oscillations which are called BAOs. Each wave expansion is decelerating everywhere and our place in
originating from such region moves around in a spherical the Universe has much less density than anywhere else
manner- outward from the overdense region. Such wave which is why our deceleration is less in comparison. In
consisted of dark matter, baryons as well as photons that case, the expansion rate of our place will be much
moving together with speed closer to half the speed of faster than anywhere else. Different parts of the space
light. (Sunyaev and Zeldovich, 1970; Peebles and Yu, expand differently in that scenario. If supernovae
1970). After 400,000 years of the big bang, the photons explode in different parts of this Universe (some close
and baryons decoupled. After that, the pressure was and some far away), we would observe different results.
relieved and a shell, with fixed radius, of baryonic matter For instance, for a distant supernova, our space expands
was left behind. This is called sound horizon. (Eisenstein much faster than the space at the location of the
et al., 2005) Later on, the matter attracted more matter- supernovae. Light coming from the supernova passes
forming galaxies and galaxy clusters. From observations through different regions with different rates of
of light from galaxy clusters, the current sound horizon expansion and the stretching of the photons produces
can be found which can be compared to that at the time redshift. However, the stretching is less in the places
of recombination. (Eisenstein et al., 2005) Thus, BAO with less expansion rate (distant) and more as the photon
can be used as standard ruler. By measuring the scale of approaches us. So, the light from the supernova would
BAO in galaxy distributions, we get a geometric probe have a smaller redshift than it would if the entire
related to the expansion history. (Frieman et al, 2008) Universe was expanding at our local rate. In contrast,
Study of CMB allows us to critically determine light in such Universe has to travel a longer distance for
cosmological parameters with high precision, which it to have a given redshift (Clifton, 2009). The
strengthens the ability of different methods to understand supernovae would appear to be dimmer in that case, just
Dark Energy. WMAP(Wilkinson Microwave Anisotropy as in the observations.
Probe) and Planck satellite data have been significant for Another possibility is that the clocks which
our study of CMB. By combining the results of data were in sync in early smooth Universe became
from BAO, CMB and Supernovae, we find that dark unsynchronized by now due to increasing lumpiness of
energy is required to explain our results. (Frieman et al, matter. Thus, time dilation has slowed down the time in
2008). However, some particle physicists ridicule the our galaxy compared to the cosmic voids out there. In
concept of vacuum energy density because the standard fact, the time shown by our clock and one in a floating
model of particle physics doesn’t allow vacuum energy void can differ by about 38 percent which can explain
density of the magnitude required to explain the the supernova data. Space is negatively curved in voids
supernovae data. The calculations predict a vacuum which implies that for a given radius, the volume is
energy 10120 times the required value which is the larger compared to a relatively flat space we live in.
biggest mismatch ever between theory and observation Wiltshire says this change in volume along with the
in the history of science. Moreover, the mass density correction to clocks can explain the acceleration.
becomes smaller as the Universe continues its expansion According to him, the Universe is slowing down in its
and yet at present, it still is about a factor of 2 of the expansion- just as it was originally thought (Gefter,
vacuum energy density (which remains constant 2008). Here is a recent review on inhomogeneous
throughout the history of the Universe) which is why cosmology for further study: K. Bolejko & M. Korzynski
many Physicists believe Cosmological Constant requires (2017) .However, Dark Energy is the most widely

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accepted explanation for the observations. the properties of Dark Energy.

𝑎 4𝜋𝐺 3𝑝 𝛬𝑐 2
2.2.5. Geometry of the Universe and Dark Energy =− 𝜌+ 2 +
𝑎 3 𝑐 3
By taking into consideration the density and pressure of
2
𝑎 8𝜋𝐺 𝑘𝑐 2 Dark Energy, the above term can be written as:
− 𝜌= − 2 𝑎 4𝜋𝐺 3 𝑝 + 𝑝𝛬
𝑎 3 𝑎 =− 𝜌 + 𝜌𝛬 +
𝑎 3 𝑐2
The above is the first Friedmann Equation. Clearly, the density of Dark Energy is added to
Here, the term containing “a” in the Left Hand Side that of density of matter (dark matter as well as normal
(LHS) is associated with the expansion of the Universe. matter) and energy (all energy except Dark Energy). This
The term containing “ρ” is associated with the resistance is what helps to flatten the curvature of the Universe.
of the Universe to expand due to the force of gravity However, we see that on RHS, the pressure term is also
from all the matter in the Universe. On the RHS, “k” is a negative when the bracket is opened. For the expansion
constant associated with the geometry of the Universe. to be accelerating, the term containing pressure should
From this equation, we can clearly see that the expansion be positive. That can happen only if 𝑝𝛬 is negative and
rate of the Universe depends upon its density. It is found large enough. This is what explains the negative pressure
that the LHS is much greater than zero. Thus, the RHS exhibited by Dark Energy. Since mass, energy and
should also be positive in that case. However, the pressure bend the fabric of space-time whose effect is
negative sign on RHS requires the “k” term to be seen as gravity; the effect of negative pressure in turn is
negative and only then will the RHS be greater than zero. seen as an anti-gravity effect which is accelerating the
The constant “k” can be -1, 0 or +1. In a expansion of the Universe.
Universe with positive curvature, the value of k is “+1”.
In a flat Universe, k is equal to 0 and in a geometry 2.2.7. Quintessence as Dark Energy
which is 3D version of a negative hyperbolic plane, the Cosmological Constant can quite well explain
value of k is “-1”. Clearly, it looks as if the Universe has Dark Energy; however there are few problems with it
a negative curvature if the equations are to make sense. which is why some scientists like to think of Dark
However, observations from CMB suggest that on the Energy to be caused by Quintessence- a dynamic field
largest scale, the Universe is almost flat! This means that evolves over time (Ratra and Peebles, 1998)
RHS is nearly equal to zero. For that, some term is The vacuum energy density would always have
added on the LHS which is a term containing to be the same. This implies that even when the Universe
“Cosmological Constant”. was 100s of magnitudes smaller, the vacuum energy
𝑎 2 8𝜋𝐺 𝛬𝑐 2 𝑘𝑐 2 density was the same as it is now. That means for every
− 𝜌− = − 2
𝑎 3 3 𝑎 10100 parts matter, physical process created just a single
part vacuum energy- something scientists think is very
Clearly, the lamda “Λ” term works on the side less likely to happen in the real world (Ostriker, 2002).
of density to flatten the curvature of the Universe. This is This is why some of them find Quintessence to be an
exactly what dark energy does! It comprises about 70% appropriate explanation for Dark Energy. ωis called
of the total mass-energy density to flatten the curvature equation of state which is the ratio of pressure to energy
of the Universe. density. For ω less than -1/3, gravity becomes repulsive.
For constant vacuum energy density represented by
2.2.6. More about the Nature of Dark Energy Cosmological Constant, ω is -1 and remains -1.
explained by Cosmological Constant: However, Quintessence has no fixed value of ω since it
evolves over time (though ω is always less than -1/3 for
𝑎 4𝜋𝐺 3𝑝 Quintessence as well due to its anti-gravity effects)
=− 𝜌+ 2
𝑎 3 𝑐 (Ostriker, 2002).
Some models suggest that Quintessence has
This is the second Friedmann Equation. The such a slow variation that it looks almost as if there is
term on LHS is related to the expansion rate of the constant vacuum density- this idea of course being
Universe. On the RHS, “ρ” represents density of mass borrowed from theories related to inflation of the Early
and energy (not including dark energy of course). The Universe. However, Quintessence is very weak
“p” represents pressure which also bends the fabric of compared to inflation and the associated time scale is
space-time. The terms on the RHS add up more than zero much longer. Since it varies with time, it cannot be a
and the negative sign means a negative acceleration is smoothly distributed component which would otherwise
produced. This would imply that the Universe is either be a contradiction with the equivalence principle
decelerating in its expansion or is collapsing towards a (Steinhardt, 2000). Physical processes are described in
Big Crunch. This is what exactly motivated Einstein to terms of field or particles, in quantum theory. Since
add a term containing Cosmological Constant to stabilize quintessence varies very slowly and has a very low
the Universe. However, the same constant can have a energy density, a particle of quintessence should be large
slightly larger value than predicted by Einstein to explain (in the scales of supercluster of galaxies) and yet be

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Nirakar et al. 2017 ISSN: 2349 – 4891

lightweight. Every field has a potential component expansion history with much better precision (than
dependent on the value of field strength and a kinetic current 10%).
component which is dependent on how field strength
varies with time; so does quintessence. Quintessence is References
“soft” in contrast to Cosmological Constant which is 1. F. Zwicky, Die Rotverschiebung von
“stiff”; in the jargon. Since every form of energy we extragalaktischen Nebeln, Helvetica Physica Acta,
know is soft to certain extent, stiffness could be an ideal 6, 110 (1933)
case which doesn’t exist. If that is so, Cosmological 2. J. H. Oort, The force exerted by the stellar system
Constant is an absolutely inappropriate candidate for in the direction perpendicular to the galactic plane
Dark Energy (Ostriker, 2002). and some related problems, Bull. Astron. Inst.
Netherlands, 6, 249 (1932)
2.2.8. MORE ON DARK ENERGY: Quintessence 3. M. Roos, Dark Matter: The evidence from
ruled out astronomy, astrophysics and
Dark Energy represented by the Cosmological cosmology,arXiv:1001.0316v2
Constant drives the Universe to expand at a constant 4. G. Bertone, D. Hooper and J. Silk, Particle Dark
acceleration over time; thus moving the galaxies farther Matter: Evidence, Candidates and Constraints,
apart, and ultimately leading to a dark-alone Universe. Phys.Rept.405, 279-390,2005
However, if the dark energy represented by quintessence, 5. M. Vonlanthen, S. Rasanen, R. Durrer, Model-
the acceleration might increase with time. Ultimately, it independent cosmological constraints from the
may pulls the galaxies, stars and even individual atoms CMB, JCAP, 08, 2010
and space itself will be torn apart- a term “Big Rip” is 6. P. Jetzer, Mircolensing Implications for Halo Dark
used to describe this event. Matter, Helv.Phys.Acta, 69,179-
However, observations from Chandra X-Ray 184,1996arXiv:astro-ph/9609016v1
Observatory (2004 A.D)on 26 galaxy clusters nearly rule 7. C.Alcock, R.A.Allsman, T.S.Axelrod et al., The
out the concept of quintessence. Moreover, it MACHO Project First-Year Large Magellanic
independently proved the existence of Dark Energy as Cloud Results: The Microlensing Rate and the
the results indicated that the Universe has stopped Nature of the Galactic Dark Halo, Astrophys.J.,
decelerating and started accelerating several billion years 461,1996
ago when Dark Energy became dominant (Michael Seeds 8. E. Corbelli, P. Salucci, The extended rotation curve
and Dana Backman, 2012). The balance between Dark and the dark matter halo of M33, R. Astron. Soc.
Matter and Dark Energy changes over time if Dark 311, 441-447, 2000
Energy is explained by Cosmological Constant. If we 9. M. Milgrom, "Does Dark Matter Really Exist?,"
look back in the past, the density of Dark Matter is much Scientific American, August 2002
higher; however, the energy density of Dark Energy 10. M. Roos, Astrophysical and cosmological probes of
should be constant. If we look back to redshift 1, the dark matter arXiv:1208.3662v3 [physics.gen-ph]
density of dark matter would be 8 times the present 11. V.C. Rubin, Dark Matter in the Universe, Scientific
density which implies that it would be about 8 times American, 1998
more significant in the past. In that scenario, gravity 12. V.C. Rubin, W.K. Ford, Astrophys. J.159, 379, 1970
would have the upper hand causing the Universe to 13. J. L. Greenstein, M. Schmidt, The Quasi-Stellar
decelerate. This is exactly what Adam Riess and his Radio Sources 3c 48 and 3c 273, Astrophysical
colleagues reported in 2004 and 2007. In fact, all the data Journal, 140, 1964
we currently have can actually fit a model of Dark 14. R. S. Ellis, Gravitational lensing: a unique probe of
Energy explained by Cosmological Constant. However, dark matter and dark energy, The Royal Society,
even precise data is significant to better understand the 2010
nature of Dark Energy. 15. C. S. Frenk, D.M. Simon, Dark matter and cosmic
structure,Ann. Phys. 2012, 524, 507
3. Conclusion 16. K.Griest, WIMPs and MACHOs,
The existence of dark matter and dark energy ENCYCLOPEDIA OF ASTRONOMY AND
have been firmly established by now. () However, the ASTROPHYSICS, 2006
origin of these phenomena remain a mystery even as of 17. E. P. Hubble, Proc. Natl. Acad. Sci. USA 15,168–
today. For dark matter, the cold dark matter described 173, 1929
above is one of the simplest explanations of our 18. N. Straumann, The history of the cosmological
observations. () Vacuum energy is the simplest constant problem, arXiv:gr-qc/0208027v1
explanation for dark energy for it is consistent with our 19. "Cepheid Variable Star RS Puppis”: NASA, ESA,
data. However, there is no theoretical understanding the Hubble Heritage Team (STScI/AURA), and H.
regarding the observed value of vacuum energy. The best Bond
solutions to these problems can be obtained after 20. R. W. Smith, E. P. Hubble and The Transformation
detection of dark matter by one of the various of Cosmology, Physics Today, April 1990
experiments designed to do so and by probing the

12
International Journal of Recent Research and Applied Studies, Volume 4, Issue 7 (1) July 2017
 Nirakar et al. 2017 ISSN: 2349 – 4891

21. M. Hamuy, M.M. Phillips, R. A. Schommer et al., 42. M. Green, The WIMP annual modulation signal and
The Absolute Luminosities of the Calan/Tololo non-standard halo models, Phys.Rev.D, 63,
Type Ia Supernovae, Astron.J. 112, 1996 043005,2001
22. S. Bergh, DISCOVERY OF THE EXPANSION OF 43. E.K. Shields, SABRE: A search for dark matter and
THE UNIVERSE,arXiv:1108.0709v2 [physics.hist- a test of the DAMA/LIBRA annual-modulation
ph] result using thallium-doped sodium-iodide
23. Guth, Inflationary Universe: A possible solution to scintillation detectors, Ph.D Thesis Princeton
the horizon and flatness problems,Physical Review University, 2015
D(Particles and Fields), 23, 1981 44. P. Sikivie, Experimental Tests of the “Invisible”
24. M. Seeds and D. Backman , Horizons: Exploring Axion, Phys. Rev. Lett. 51, 1415 (1983).
the Universe, 12th Edison, 2012 45. N. Benitez, R. Dupke et al., J-PAS: The
25. G.R. Adam et. al, OBSERVATIONAL EVIDENCE Javalambre-Physics of the Accelerated Universe
FROM SUPERNOVAE FOR AN Astrophysical Survey arXiv:1403.5237v1 [astro-
ACCELERATING UNIVERSE AND A ph.CO]
COSMOLOGICAL CONSTANT, Astron.J.,116, 46. E. G. M. Ferreira, J. Quintin, A. A. Costa, E.
1009-1038,1998 Abdalla, B. Wang, New evidence for interacting
26. S. Perlmutter et al., MEASUREMENTS OF dark energy from BOSS arXiv:1412.2777v3 [astro-
OMEGA AND LAMBDA FROM 42 HIGH- ph.CO]
REDSHIFT SUPERNOVAE, Astrophys.J., 517, 47. Dark Energy Survey Collaboration: T. Abbott, F. B.
565-586,1999 Abdalla, J. Aleksic, et al., The Dark Energy Survey:
27. Slipher, Proc. Amer. Phil. Soc., 56, 403, 1917 more than dark energy - an overview, MNRAS,
28. S. Perlmutter, Supernovae, Dark Energy, and the 460, 1270 (2016)
Accelerating Universe, PHYSICS TODAY, April 48. Dark Energy Survey Collaboration: T. Abbott, G.
2003 Aldering, J. Annis, et al., The Dark Energy Survey,
29. W. Li and A. V. Filippenko, Observations of Type Ia arXiv:astro-ph/0510346v1
Supernovae and Challenges for Cosmology 49. E. Hubble, Mi. L. Humason, The Velocity-Distance
30. T. Clifton,P.G. Ferreira, Does Dark Energy Really Relation Among Extra-Galactic Nebulae, Astro-
Exist?, Scientific American 300, 48 - 55 2009 physical Journal, LXXIV, 43-80, 1931
31. P.J.Steinhardt, Quintessential Cosmology and 50. A.Guth, Inflation and Eternal Inflation, Phys.Rept.
Cosmic Acceleration,Bl. Schwerpunkt ,333, 2000 arXiv:astro-ph/0002156v1
Astroteilchenphysik, 2000 51. D. Clowe, A. Gonzalez, M. Markevich, Weak
32. J. P. Ostriker and P. J. Steinhardt, The lensing mass reconstruction of the interacting
Quintessential, Scientific American, 284, 2001 cluster 1E0657-558: Direct evidence for the
33. A.Gefter, Dark energy may just be a cosmic illusion, existence of dark matter,Astrophys. J.,604(2), 596–
New Scientist, March 2008 603, 2003 arXiv:astro-ph/0312273
34. A.Riess, Seeing Dark Energy, Proceedings of doi:10.1086/381970
"Identification of dark matter 2008". August 18-22, 52. M. Markevitch, S. Randall, D. Clowe, A. Gonzalez
2008, Stockholm, Sweden, p.43 et al. Dark Matter and the Bullet Cluster. 36th
35. H. Peng, S. Asztalos, E.J. Dawet al., Cryogenic COSPAR Scientific Assembly. Beijing, China, 2006
cavity detector for a large-scale cold dark-matter 53. R. Scarpa, Modified Newtonian Dynamics, an
axion search, Nucl. Instrum. Methods A, 444, 569– Introductory Review, 2006
583, 2000 54. P. Gondolo, Non-Baryonic Dark Matter, 2004
36. S. J. Asztalos,G. Carosi, C. Hagmann et al., arXiv:astro-ph/0403064v1
SQUID-Based Microwave Cavity Search for Dark- 55. D.J. Eisenstein, et al., Detection of the Baryon
Matter Axions, Phys. Rev. Lett., 104, 2010 Acoustic Peak in the Large‐Scale Correlation
37. D.B. Tanner; Search for Axionic Dark Matter, Function of SDSS Luminous Red Galaxies, The
Patras 2013 Astrophysical Journal, 633 (2): 560,
38. K. Yamamoto, M. Tada, Y. Kishimoto et al., The 2005 arXiv:astro-
Rydberg-Atom-Cavity Axion Search arXiv:hep- ph/0501171.Bibcode:2005ApJ...633..560E. doi:10.
ph/0101200v1 1086/466512.R. Sunyaev.; Ya. B. Zeldovich, Small-
39. N.C. Spooner, Vitaly Kudryavtsev, The Scale Fluctuations of Relic Radiation, Astrophysics
Identification of Dark Matter, 2002 and Space Science., 7 (1): 3,
40. S. Akeribb, X. Baih, S. Bedikianq et al., Nuclear 1970 Bibcode:1970Ap&SS...7....3S. doi:10.1007/B
Inst. and Methods in Physics Research, A704, 2013 F00653471
41. V. Barger, W.Y. Keung, D. Marfatia et al., 56. P. J. E. Peebles, J.T. Yu, Primeval Adiabatic
PAMELA and dark matter, Phys.Lett.B, 672, 141- Perturbation in an Expanding Universe, The
146,2009.. Astrophysical Journal. 162: 815,
1970 Bibcode:1970ApJ...162..815P. doi:10.1086/15
0713.

Please cite this article as: Nirakar Sapkota & Binod Adhikari (2017). Dark Matter and Dark Energy: Mysteries of
the Universe. International Journal of Recent Research and Applied Studies, 4, 7(1), 1-13. 13
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