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Baryonic matters or just ordinary matters are the kinds of matters that we can see, touch, feel, taste, observe like electrons, protons, neutrons, atoms. Even our body, as well as everything visible around us, is baryonic matters. Whenever we take this entire universe into an account, we find the existence of a matter which is non-baryonic, popularly addressed as ‘Dark matter’. Dark matter doesn’t commonly react with ordinary matter and even invisible to us. It seems as if our universe is haunted by invisible matter and energy. Scientists and cosmologists are pretty sure they exist though.

REALITY AND LIMITATION

Audible Range Of Human Ear
Visible Range Of Human Eye
Limitations Of The Human Eye And Ear

The same goes for dark matter too. Dark matter and dark energy play an important role in the stability of our universe.

HISTORY OF DARK MATTER

(If you are fixated to know more about the topics like introduction to dark matter, dark matter boon or curse for humankind, evidence of dark matter, etc, you can skip this section). Furthermore, you will find a summary of the history of dark matter in the section; What really is dark matter.

Sir Issac Newton published a comprehensive ‘Theory Of Gravity’ in 1687. This universal law of Gravitation intellectually explained the Gravitational binding energy of smaller bodies to heavenly bodies like planets, stars, etc.

Sir Issac Newton

Soon after Newton’s theory of universal gravity, some astronomers and cosmologists started hypothesizing the object that might not emit light but traces could be detectable through its gravitational impact on bright and massive objects like stars and planets.

Massless

The hypothesis robustness was accelerated in the 1700s, when Pierre Laplace conceptualized that some objects might be massive enough to trap light particles, more like the concept of a black hole.

In 1884, Lord Kelvin intended to measure the mass of the galaxy through the velocity dispersion of stars orbiting around the center of the galaxy. He estimated that mass of galaxies that he determined was annoyingly different from the mass of luminous stars. Lord Kelvin thus concluded that the great majority of stars could conceivably be non-luminous and even do not reflect light, maybe dark bodies (invisible bodies). Some general public even termed this as ghost mass. It was noteworthy.

Lord Kelvin

By this point, astronomers were confident that there was much more in the universe except just visible bodies. Lord Kelvin’s discovery led to many debates among astronomers for decades like by French astronomer Henri Poincaré in the year 1906, and he referred to that matter as an unknown matter.

The haunted universe

In 1920, Edwin Hubble observed that the universe seemed to be expanding rather than being motionless. Edwin even noticed that we are addressing galaxies in terms of nebulas. He turns out to be right. Edwin studied about Coma cluster and calculated the mass of it.

Edwin Hubble

The foremost existence of dark matter using stellar velocities was proposed by Dutch astronomer Jacobus Kapteyn in the year 1922. Jan Oort also hypothesized the existence of dark matter in 1932. Dutch astronomer Jan Oort measured the orbital speed of stars within the Milky Way and found that they moved too rapidly to be explained by the observed mass of the galaxy.

Jacob Kapteyn

The major aspect astronomers hoped to measure was the mass of a galaxy. Something as massive as galaxies can’t be measured directly. There are several proved and tested scientific theories to calculate the mass of a distant galaxy. One method is to measure the light intensity or luminosity. The more luminous a galaxy, the more mass it possesses. Another option is to calculate the rotation of a galaxy’s body by tracking how quickly stars within the galaxy move around its center. Variations in rotational velocity should indicate a region of varying Gravity and therefore mass.

The remarkable contribution to the dark matter stuff was in 1933 by Swiss astrophysicist Fritz Zwicky while working at the California Institute Of Technology.

Coma Cluster

The Coma cluster is a galactic supercluster containing more than 1,200 galaxies. Fritz Zwicky studied the motion of galaxies within a coma cluster using the Virial theorem. Zwicky was perplexed by the relation between gravitational forces and the movement of galaxies. He found that the galaxies were moving too quickly to remain gravitationally bound within the cluster. Zwicky estimated its mass based on the motions of galaxies approaching its edge and compared that to an estimate based on its brightness and number of galaxies. After several days of restlessness and maths, Zwicky successfully calculated the cluster’s mass. His calculation of mass was immensely greater than Edwin Hubble’s calculation, more than 400 times. Edwin Hubble’s calculation was based more upon visually observable bodies. Zwicky called this unseen mass Dunkle Materie (‘dark matter’). Zwicky authoritatively concluded that if his observation and measurement are true, then mass discrepancy is all due to dark matter (invisible matter) which dominates the ordinary matter to a greater degree. The dark matter was known by ‘The Missing Mass Problem’ at that time.

Fritz Zwicky

In the 1930s, Knut Lundmark was again measuring the difference of the mass that we calculate to be in a galaxy compared to the amount of mass suggested by light. This is called mass to light ratio. He found that it was somewhere 100 times more mass than light we could see for a galaxy called Messier 81. He put forward a fact that the distribution could only properly be explained if the galaxies contained vast amounts of light-blocking dark clouds.

Knut Lundmark

Over the next couple of decades, the virial theorem was applied to numerous galaxy clusters with similar results. The virial theorem is a statistical calculation based upon certain assumptions like the clusters are gravitationally bound. That’s why it didn’t receive much popularity for some years. Zwicky’s calculation and maths were taken as absurd. Nevertheless, Zwicky did correctly conclude from his calculation that the bulk of the matter was dark. However, there was one thing that couldn’t be denied and also supported the existence of dark matter — the galactic rotation curve.

The rotation curve shows how faster the stars are rotating around the center of the galaxy at an increasing radius of the galaxy.

In 1939, Horace W. Babcock published his Ph.D. thesis in which he measured the rotation curve of the Andromeda galaxy which suggested that the mass to luminous intensity (mass to light ratio) increases radially.

Horace W. Babcock

(The rotation curve will be described more fully in evidence for the dark matter section).

By 1957 Hendrick C. Van de Hulst, Ernst Raimond, and Hugo van Woerden were the first people to obtain a rotation curve of the Andromeda galaxy, not in optical light but radio light. They were detecting the emission in radio wavelength at 21 centimeters from Hydrogen gas in the Andromeda galaxy. Ultimately, this curve was flattened too, thereby acknowledging the notion of dark matter.

In 1970, Ken Freeman found that the rotation curves for several galaxies disagreed with expectations based upon the assumption — that the galaxies consisted of stars, gas, and nothing else. Freeman reasonably suggested that these galaxies, like the Coma cluster, observed much earlier by Zwicky, contained considerably more invisible dark matter than the luminous matter.

In 1974, Ostriker et al. stated that the currently observed rotation curves strongly indicated the excessive presence of dark matter.

In 1980, An influential paper presented Vera Rubin and Kent Ford’s work of the 1960s and 1970s upon the rotation curve of spiral galaxies.

Vera Rubin

Their discoveries were based on a new sensitive spectrograph. It could measure the velocity curve of edge-on spiral galaxies better than it had ever been achieved before. It showed that most galaxies must contain about six times as much dark as visible mass to maintain such incredible quick rotation and stability. Otherwise, they should throw themselves into pieces spinning that quickly.

By around 1980, the apparent need for dark matter was widely recognized as a major and the longest-standing unsolved problem in astrophysics.

Error

From then on (the 1980s), the theory of dark matter has been refining further and further as we’ve learned more about our universe, leading to some fascinating evidence and some controversial theories as well; Gravitational lensing, questioning the validity of Newtonian mechanics, and even modifying Newtonian mechanics. (We will soon discuss the modified Newtonian dynamics, at the end of this article).

Now the most scientists and cosmologists are quite certain that dark matter is abundant in the universe and has got the inexplicable property of neither absorbing light reflecting light. The impact of dark matter is greatly seen in the structure of galaxies.

That’s how the term dark matter has got a history over centuries back.

WHAT REALLY IS DARK MATTER

For centuries Scientists/cosmologists/astrophysicists/astronomers were surprised to discover the Gravitational impacts that stars, planets, and galaxies possessed as it was not sufficient from the mass that we obtained through visible stars and bodies. It means there is some kind of mass that doesn’t reflect light but responsible for holding indescribable Gravitational impact and structure. This is where the concept of dark matter arises.

Dark matter is the form of matter that accounts for approximately 85% of the total matter in our universe.

Dark-Matter Percentage

According to Lambda – CDM model of cosmology, the total mass-energy of the universe contains 5% ordinary matter and energy, 27% dark matter, and 68% the form of energy referred to as dark energy. Dark energy is credited for making the Universe larger, in essence, acceleration of space expansion.

We can see only those objects which either absorb/reflect light or itself is a source of light. Dark matter is called dark because it does not appear to interact with the electromagnetic field which means it doesn’t absorb, reflect or emit electromagnetic radiation (like Light) and is therefore difficult to detect.

Dark matter has not been observed directly yet. According to astrophysicists, dark matters barely show its effect with ordinary baryonic matter and radiation, except gravity. This is why Dark matter is thought to be non-baryonic.

 HOW IS DARK MATTER DIFFERENT FROM ANTIMATTER?

The particles like electrons, protons, quarks, atoms, etc form matter, while antiparticle like anti-electron (Positron), antiproton, antiquark, etc form antimatter. For every particle, there exists antiparticle too. As an analogy, the squared root of 9 has two solutions, i.e., +3 and -3. Mathematically, these values cancel each other, zero.

Matter/Anti-Matter

Matter and antimatter are identical but with the opposite property. One is positively charged, then another one is negatively charged. Whenever they meet each other, they annihilate each other producing unique gamma rays.

Since dark matter is distributed abundantly in the universe, there must be gamma rays everywhere in the galaxy clusters but is not the case. It proves that dark matter and antimatter are not the same things.

IS DARK MATTER AROUND US?  IS DARK MATTER CURSE FOR HUMANKIND? WHY DOESN’T DARK MATTER REACT WITH OUR BODY PARTICLES?

Yes, dark matter is around us. Every second more than millions of dark matter are passing through everyone around us. Baryonic particles like electrons, protons, neutrons, etc give rise to atoms. Atomic combinations led us to molecules, whereas molecular combinations are what we call the building block of the body, i.e., cells. Our body contains millions and millions of cells and atoms.

According to scientists, preferring living bodies for the detection of dark matter will not be safe. Scientists theorized that dark matters can interact with ordinary matter in clumps or so-called macros.

The energy of one macro can achieve the same energy as the bullet fired from a 22 caliber rifle. The clumps of dark matter are invisible and quite smaller in size as well.

Sun’s Temperature


However, the Collision of dark matter with the human body will produce a temperature equivalent to 1.74 times greater than the temperature of our sun that works out to be 10 million degrees kelvin.

By some crazy scientific experiments, if we can transform every matter of our body into dark matter, then entire particles of our body will disintegrate (Literally, the disintegration of every atom). The disintegrated particles will circle in an elliptical orbit around Earth’s core at the speed of 3 km/s because of the effect of Earth’s Gravity, as this speed is insufficient to escape Earth’s gravity. Moreover, the fundamental forces of our universe will not show up any effects that do with ordinary matters.

disintegrated particles
Disintegrated Particles

When dark matters interact with our body particles, dark matters transform themselves into cylinders of plasma. And in such extreme temperatures, it is enough to make a plasma hole throughout our body. In case the massive amount of dark matter collides with a living body, then entire body particles will disassociate turning into a complete plasma.

Even though dark matter counts out to be more than millions around us, we have never encountered someone dying because of dark matter so far. The science behind this has got an explanation with very basic terminology — density. The mass contained by a body per unit volume is called density.

For years, scientists were pretty sure that our galaxy cluster has six times more dark matter than ordinary ones. The most notable thing here is the concentration/density of dark matter. The density of dark matter is maximum at the center of the galaxy, while quite low at the outskirts.

Milky Way Galaxy

Milkyway galaxy is our home. More generally, the solar system is our home. Our Solar system consists of numerous asteroids, comets, and planets. The solar system is 25,000 light-years away from the center of the Milkyway galaxy.

1 Light Year = 9.46 × 10^12 KM

Even if we add up all the masses of dark matter of our Solar system, it will be just 10^17 kilograms which are not even massive as an average size of the asteroid.

Furthermore, the Density of the human body is 1000 kg/m^3. Meanwhile, the density of dark matter is just 10^-12 kg/m^3. Density is a very basic term, and we can even perform some maths to calculate the amount of dark matter passing through a human body.

Scientists estimated that 10^-22 kilograms of dark matter pass through us at any given point in time. Likewise, every second it will sum up to 2.5 × 10^-22 kilograms. Each year around 10^-8 kilograms, while in 81 years (the average human life expectancy), it will be just around 1 milligrams.

 WAS DARK MATTER RESPONSIBLE FOR PAST CATASTROPHE?

Dinosaurs Extinction

According to Harvard University Physicists Lisa Randall and Matthew Reece, dark matters could have been the indirect causes of mass extinction of lives and properties. It may happen again.

Matthew Reece
Lisa Randall

When Dinosaurs ruled the Earth, the planet was on a completely different side of the galaxy.

Dinorsaurs Extinction

Our Sun orbits the galaxy’s center, completing its rotation every 250 million years or so. Many of the most iconic dinosaurs roamed Earth when the planet was in a very different part of the Milky Way.

Michael Rampino (Geologist and Professor of Biology and Environmental Studies at New York University) believes that once every 26 to 30 million years, our Solar system will face a dense disc of dark matter. These dark matters settle into Earth’s core which makes dark matter clumps denser eventually destroying each other. This destruction led to an enormous increase in temperature of the Earth’s core, provoking magma to cause strong volcanic eruptions. The aftermath of these volcanic eruptions may give rise to the formation of new continents, destruction of countless lives and properties as well. Considering the preciousness of time, dinosaurs explored our blue and green globe for about 165 million years. Life will find its way.

EVIDENCE FOR DARK MATTER

★ Galactic rotation curve: The rotation curve of the disc galaxy is a plot of orbital speeds of visible stars or gas in that galaxy versus their radial distance from that Galaxy’s center. This is also called a velocity curve. To make a rotation curve, one calculates the rotational velocity of stars along the length of a galaxy by measuring their Doppler shifts and then plots this quantity versus their respective distance away from the galactic center.

For simplicity, this is just a graph of distance versus velocity. We can even do this with our solar system. Through visible light observation Spectra (mass to light ratio), most galaxies have the bright centers as seen in normal light and keep on dimming as we move far away from the Centre. The luminous mass density of a spiral galaxy decreases as one goes from the center to the outskirts. If luminous mass were all the matter, then we can model the galaxy as a point mass in the center and test masses orbiting around it. This does mean the most of the stars/mass is located at the center of the galaxy. If that’s the case, one would expect stars far from the center to move slower than stars near the center as from Kepler’s second law, it is expected that the rotation velocities will decrease with distance from the center, similar to the Solar System. Kepler’s laws failed to explain in the case of the galaxy. Prediction and observation vary a lot.

In 1939, Babcock observed the scenario to be the complete opposite. Invariably, it is found that the stellar rotational velocity remains constant giving us a flat curve. Though his measurements weren’t precise enough, it would still be impossible to get an increasing flat curve.

Curve Predicted VS Observed

It describes that the rotation speed is found not to decrease with increasing distance from the galactic center. This signifies that stars moved at the same speed regardless of their distance from the galactic center, also implying that the galaxy must be surrounded by a halo of dark matter (which means the Galaxy’s mass is not concentrated in the center of the galaxy). Moreover, in the case of our solar system, Kepler’s second law works pretty perfectly because the majority of the mass of our solar system is concentrated in the sun alone, around 99 % of the total mass of our solar system. The circumstances are pretty different for galaxies as they contain a massive amount of dark matter even on the outskirts, regardless of mass located just at the center.

Mathematically, the mass must continue to increase as the rotation speed satisfies the equation:  

                       V^2 = GM/r 
                       
we get this by equating centrifugal force with gravitational force.

where M is the mass within radius r, G is Newton’s universal Gravitational constant, and V is the rotation velocity.

This is the case with the Andromeda galaxy and has been observed by many astronomers like Max Wolf and Vesto Slipher. This has been applied to numerous other galaxies a plethora of times, leaving similar results every time, and thus supporting the presence of dark matter.

★ Stability of galaxies: Gravitational force plays a vital role in the stability of our universe. Our universe is comprised of billions of galaxies. Galaxies may contain trillions of stars, asteroids, numerous planets, and many more else. The way our universe functions is quite flawless like the rotation of planets around the sun, rotation of the moon around the planet, etc. These phenomena drive the astronomical changes. The solar system is not just an ordinary part of the milky way galaxy but is the quintessential part serving as the home for the human race since the beginning. What if the Earth is no longer accompanied by regular astronomical changes; day/night cycle, seasons, etc.

Although we add up the magnitude of gravitational impacts of stars, galaxies, dust, planets, etc, then it seems like they have some kind of mysterious Gravity. All the baryonic masses that we see in our universe are insufficient to produce gravitational binding energy that could bind and hold all the stars, galaxies, and planets and dust together.

Newton’s Law Of Universational Gravitation

It is only possible if galaxies consist of five to six times more mass than we can observe, meaning that galaxy, stars, planets would scatter/fly away in space with such poor gravitational binding energy suggested by visible bodies.

But in our universe, we see stars, planets, and else following the pretty regular gravitational phenomena leading to the formation of complex galaxies and complex structures like our own Milky way galaxy.

Hence, the Gravitational binding energy supports the existence of dark matter. We are still avoiding one thing. How we could ignore the fact that the universe is expanding. Here comes the energy, the dark energy.

DARK ENERGY

Dark energy is even more mysterious and strange than dark matter. Anciently, Physicists had assumed that the attractive force of gravity would slow down or even retract and collapse in on itself at some point over time. When scientists tried to measure the rate of deceleration, they found that not only everything moving apart from each other, but the universe expansion also seems to be accelerating.

Expanding Universe

Scientists now think that the accelerated expansion of the universe is driven by the kind of repulsive force generated by quantum fluctuations (in otherwise empty space). Empty space doesn’t mean there is no any kind of energies. Not only this, the force even getting stronger over time. Therefore, Scientists called this mysterious force ‘Dark energy’. Scientists have still not much clue about what dark energy is. According to one approach, dark energy is a fifth type of fundamental force (electromagnetic force, gravitational force, Nuclear force) called quintessence, which fills the universe like a fluid.

Dark energy is the repulsive force (antigravity) which tends to accelerate the expansion of the universe, while dark matter is responsible for attractive force (Gravity) which binds the stars, galaxies, planets, and else in a stable state.

Einstein’s Biggest Blunder

In 1915, Albert Einstein discovered the “General Theory of Relativity”. Einstein believed the universe to be static and eternal. Einstein’s field equation is an important aspect of this theory. It is the set of the equation that relates the curvature of space-time to the amount of matter and energy moving through a region of space-time.

Albert Einstein Field Equation

Einstein wasn’t happy with this equation as this equation clarifies that the universe seemed to be stretching or contracting which was against Einstein’s static universe belief.

Albert Einstein Modified Equation

Einstein added one more term to the left side of his equation, and he called it the cosmological constant.

In 1929, Edwin Hubble examined how the wavelength of light emitted by distant galaxies shifts towards the red end of the electromagnetic spectrum as it travels through space. He found that fainter, more distant galaxies showed a large degree of redshift and for closer, not much. Hubble concluded that the redshift occurred because the wavelength of the lights was stretched as the universe expands, and thereby the universe itself is expanding. More recent studies even showed that the expansion rate is accelerating.
 

Edwin Hubble

Thus, Einstein called the cosmological constant his biggest blunder. According to Einstein, the constant would be the repulsive force that stabilizes the inward pull of gravity. But this is not the end.

Albert Einstein

Since our Universe is expanding and accelerating, the adding of cosmological constant could effectively explain dark energy. Einstein’s blunder even turned out to be describing the actual scientific phenomena of our universe. However, scientists are still not sure what set this weird force to exist in the universe.

★ Gravitational Lensing: According to Einstein’s General Theory of Relativity, the space-time can bend, flex, and warp under the influence of mass and energy. One of the most remarkable components of Einstein’s theory of general relativity is that Gravity bends light. When astronomers refer to lensing, they are talking about an effect called gravitational lensing.

Gravitational lensing is a phenomenon in which massive object like galaxy clusters can act as a lens and is capable of bending the light as well as distorting the images of objects lying beyond that mass forming multiple images. This effect is analogous to that produced by the lens. How some lenses can converge or diverge light, while stick submerged in water appears bent. Similarly, lenses used in a magnifying glass works by bending light rays that pass through them in a process known as refraction through which one can focus the light, wherever he desired to. The gravitational field of a massive object covers a vast region into space that causes light rays passing close to that object to be bent and refocused somewhere else giving arise to multiple images.

Refraction Of Light

Large galaxy clusters contain massive amounts of ordinary matter and dark matter, within and around the galaxies. Galaxy clusters are massive and can act as strong gravitational lenses. Although astronomers cannot see dark matter, they can detect its influence by observing how the gravity of massive galaxy clusters, which contain dark matter, bends and distorts the light of more-distant galaxies into arcs located behind the cluster. The lensing effect is directly proportional to mass (the lighter the object, the lesser the lensing and vice versa). This method can be used to measure the total mass of the cluster by measuring the distortion geometry of light. Once you cancel out the gravitational effect of visible matter, what you have left is the gravitational effect of dark matter. In many clusters, this method has been used and it is estimated that a large fraction of the mass of the clusters is composed of dark matter. In a lot of cases where this has been done, the mass-to-light ratios obtained always correspond to the dynamical dark measurements of clusters, implying that the Universe actually appears to have about five times more dark matter than regular matter.

Virtual images of the galaxy


The lensing effects result in multiple copies of images as we discussed earlier. Likewise, by analyzing the distribution of multiple image copies; Scientists have been able to map the distribution of dark matter around the different galaxy clusters. And now, by studying where that lensing appears in the sky, an international team of scientists has released a detailed, 3D map distribution of dark matter.


Here’s one cool story of the Hubble space telescope showing the application of Gravitational Lensing. (You may skip this).

Through the Hubble Space Telescope, Astronomers were successfully able to hunt a quasar (the region around active black holes where superheated matters emit tons of light) that almost perfectly aligned behind an entire massive galaxy. The gravity from the galaxy bends the quasar’s light in such a way that it is visible to Hubble; in fact, galaxies can magnify the quasar and copies it’s images four times. Those four images were not identical. They got distorted by dark matter that warps the space that quasar’s light travels through. The four distorted images fascinated astronomers, providing evidence for dark matter.

Furthermore, multiple images of an object appear when the lens is extremely massive, and such lensing is called strong lensing. However, even small and light objects like we, planets, etc can make a lensing effect with minute distortion. The lensing effect takes place on all scales. By definition, everything in the universe can act as a gravitational lens; your observational technique just has to be sensitive enough to detect the lensing. Weak Gravitational lensing has even been proved by characterizing the mean distribution of dark matter through studying apparent shear deformation of the adjacent background galaxies. The mass-to-light ratios obtained correspond to dark matter densities predicted by other large-scale structure measurements.

★ Cosmic Microwave Background Radiation:  In 1964, astronomers Arno Penzias and Robert Wilson were working on a radio telescope that could detect microwaves and radio waves coming from space. They accidentally found the evidence of the big bang theory called cosmic microwave background radiation. These are the microwaves which were the afterglow of the big bang when our universe was way too young, and even present everywhere in space now too and will. This was the first direct proof of ‘The Big Bang Theory’.

In the early universe, the ordinary matter was ionized and interacted strongly with radiation via Thomson Scattering. Dark matter does not interact directly with radiation, but it does affect the CMB by its gravitational potential (mainly on large scales), and by its effects on the density and velocity of ordinary matter. Therefore, Ordinary matter and dark matter evolve differently with time and leave different imprints on the cosmic microwave background. The cosmic microwave background is very close to a perfect blackbody but contains very small temperature anisotropies of a few parts in 100,000. A sky map of anisotropies can be decomposed into an angular power spectrum, which is observed to contain a series of acoustic peaks at near-equal spacing but different heights.

The observed CMB angular power spectrum provides powerful evidence in support of dark matter, as its precise structure is well fitted by the Lambda-CDM model.

WHAT DARK MATTER IS MADE UP OF?

In general, scientists know more about what dark matter is not than what it is. No onehas observed dark matter directly yet. However, they still got some possible hypothetical candidates for dark matter.

Hypothetical particles

Since dark matter is thought to be non- baryonic, the subatomic particles that go beyond the standard model of particle physics could account for these observations.

 1. The WIMPs


The most famous/popular candidate for dark matter is WIMPs (Weakly interacting massive particles). It is a hypothetical particle but looks very promising in this case. It will be different from ordinary matter as we expect to be non- baryonic, i.e., doesn’t interact with electromagnetic radiations. According to WIMPs analysis, it clarifies there must be about five times more of these matters than normal matter which may collide with the abundance of dark matter that we observe in the Universe. It characterized that we should be able to detect them through their collisions as this would cause the charged particles on Earth to recoil, producing light that we can observe in experiments such as XENON100.

2. The Axion

Axions are low-mass, slow-moving particles that don’t have a charge but can interact weakly with other matter. It is quite bothersome to detect but not impossible still. The particular kind of axions like one with specific mass would be able to explain the invisible nature of dark matter. And if axions do exist, (heavier or lighter matters not) they would be able to decay into a pair of a light particle (photons) which means we could detect them by looking for such pairs. The ‘Axion Dark Matter Experiment’ works upon this principle and looking for the search for dark matter.

Likewise, they may even be supersymmetric particles or some kind of neutrino or any number of other exotic particles. That has been postulated but all remain in the hypothetical realms.

MODIFIED NEWTONIAN DYNAMICS

In 1983, Mordehai Milgrom predicted that what if the gravity is not due to dark matter but the failure of Newtonian mechanics (theory of motion, the universal theory of gravity) itself.

Mordehai Milgrom

He proposed the modification of Newton’s universal Gravity known as Modified Newtonian Dynamics (MOND). The idea is that; all of the observations could be explained just by considering simple correction like Force equals mass times acceleration squared rather than just mass times acceleration. In the same manner, Newton’s law of gravitation might vary between short distances like our solar system and large distance like entire galaxies clusters. This proposal doesn’t need only the modification of Newtonian mechanics but also the modification of Einstein’s ‘General Theory Of Relativity’. By the 1980s, several alternative gravitational models appeared. These models worked well for dwarf galaxies, but they did pretty bad with things like entire galactic clusters. New proposals keep on popping and helping us figure out the mystery of dark matter.

 MODERN APPROACH TO DARK MATTER

Some astrophysicists even argue whether dark matter is a matter or not, but they are quite sure that whatever it may be it behaves very similarly to Gravity. Scientists are trying hard to detect dark matter particles up in the sky as well as even in underground mines. In underground mines, they are waiting for possibilities that dark matter particles that go through Earth would hit denser material and leave traces of it. In Sky, they wish for possibilities that dark matter particles Collision would create high energy light so that it could be detectable through special ‘Gamma-Ray Telescope’. Likewise, The Large Hadron Collider in Switzerland has contributed much to the mystery of dark matter. But with every theory and technological development, the secret of the invisible cosmos will come closer to being revealed.

— Sudip Karn

References :


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