The science behind Dark Matter
In 1930, a Swiss scientist named Fritz Zwicky, while studying a coma cluster of galaxies noticed something abnormal about the way they moved. The galaxies were moving way too fast, so fast that they ought to have been flying separated from each other because all the stars in all those galaxies had dreadfully little gravity to hold the cluster together. Zwicky’s idea, that something different must be binding all these things together, and that mysterious missing segment would have to weigh something like 50 times as much as the stars themselves, however at that time no one paid much attention to his crazy assumption.
If we observe our solar system, the deepest planets like mercury, Venus, and earth rotate around the sun much faster than outermost planets like Uranus and Neptune. Theory of Relativity clarifies this development and variation of speeds of these planets since the planets close to the sun will experience strong gravitational force resulting in them moving at a faster rate, where the outermost planets will rotate comparatively at a slower speed because of weak gravitational force they experience.
We will anticipate that these laws of physics should apply to all the planets and all the galaxies. And that outermost stars in a galaxy should give us the same result as our solar system gives.
Yet, in 1970, a cosmologist named Vera Rubin while examining the Andromeda galaxy, found that the outermost planets don’t comply with these laws of relativity. The outermost stars in the galaxy were revolving around at the same speed as the innermost stars. This speed was way faster than the laws of physics advise us. Rubin studied more galaxies to check whether they obey the planetary laws of physics but out of 60 galaxies she studied, she got a similar outcome for every one of these galaxies.
This perception doesn’t mean that the laws which Newton gave us weren’t right but that, there exists an enormous undetectable force or particles whose gravity was bringing this change in their speed. This unknown matter whose force of gravity was defying all the laws of physics was “Dark Matter” which Fritz Zwicky had observed in 1933 in particular. We cannot see or observe this dark matter. The only way we know that it exists is because of anomalies in gravity that we see in our universe.
Out of the total energy and mass which exist in our universe about 73% is dark energy, 23% is dark matter, and the remaining 4% is just a tiny bit of total energy that we have been able to discover.
But how do we know something exists if we can’t see it. About 22 years ago, in 1988 two projects naming Supernova Cosmology Project and High-Z Supernova Search Team, discovered that the speed of expansion during the very early universe was far shorter than the current speed of expansion of the universe. Our galaxies are not only expanding but they are accelerating. We assumed that this expansion would be slowed down due to mutual force between the planets. In any case, this expansion will require gigantic energy to accelerate the whole universe which we today know as dark energy.
But how can a universe remain intact while experiencing this massive force? There must be something that is keeping all the things together in the universe. To keep all these stars and planets together there should exist something with at least 80–90% of the mass of these all-stars combine.
Albert Einstein portrayed gravity as a curvature of time and space. Anything with mass should curve space around it. A picture from the Hubble space telescope in which astronomers pointed the telescope at the galaxy cluster RCS2 032727–132623, which is 10 billion light-years from Earth. This distant galaxy was three times bigger than any other seen through a telescope. These astronomers discovered a phenomenon that now we know as gravitational lensing. Gravitational lensing is created when a massive object, like a black hole or galaxy cluster, falls in between an observer like Hubble Telescope. In an ideal case, light comes from all the sides of the object creating a ring which is also called as Einstein Ring. Hundreds of gravitational lenses are currently known and half a dozen of them are partial Einstein Rings. Using these gravitational lenses also known as arcs we found that they contain about 90% more mass than anticipated.
These galaxies show us that a mysterious type of particle known as dark matter, an undetected and invisible force binding these galaxies together exists.
Another evidence of dark matter is Cosmic Microwave Background (CMB). CMB is otherwise called relic radiation, is faint cosmic background radiation filling all the space or we can say a faint afterglow of the universe’s birth in the Big Bang. Around 400,000 years after the big bang, the universe had sufficient time to cool and allow protons and electrons to form neutral hydrogen. This process is also known as “Recombination”, set the cosmic microwave background radiation-free from a cloud of plasma in which it was trapped. Our space telescopes like Planck and WMAP have been able to identify this radiation throughout the sky in the (1–400) GHz range, with a temperature of about 2.7 K.
The hypothesis is that the matter which is distributed in the observable universe isn’t very homogeneous and isotropic. This matter can be found in the form of galaxies, clusters, etc. These large-scale structures are formed by gravitational instability from small initial fluctuations that have been set up very early in the universe. We can see these initial fluctuations in the CMB.
This discloses to us that the greater part of the matter in the universe known to mankind is in the form of obscure non-baryonic segments which does not interact with photons. That is why we can’t see this matter. It also tells us that this baryonic matter is in the form of gas which does not transmit visible light. X-ray observations show that a part of (about 10%) dark matter in the cluster is in the form of hot gas emitting X rays.
There has been more clarification educating us about what this dark matter could be. Some of them are Neutrino, Sterile Neutrino, Neutralino, Axion, Black Hole, Wimpzillas, and Gravitinos etc.
Dark Matter is also known as WIMP (Weakly Interacting Massive Particles) meaning dark matter does not interact with the normal matter of which we and most of the known universe are made off. Because of its weakly interacting nature, we can’t detect it. Since we can’t observe this dark matter, CERN which is a European research organization, the largest particle physics laboratory situated in Geneva, Switzerland is attempting to recreate the conditions of the big bang to study particles at an unprecedented level. Since we know that dark matter was created in the process of the big bang where all other types of matter were created. If we can recreate the big bang condition we will be able to produce the dark matter.
So, is it practically possible to create dark matter? We’ve yet to directly observe the dark matter, however, scientists have theorized that we might be able to create it. The Large Hadron Collider (LHG) is the world’s largest and most powerful particle accelerator. It is spread over 27 kilometer-long situated in Geneva, Switzerland.
In the LHC, two proton beams move in the opposite direction and travel at near the speed of light. There are four points where the beam pipes are made to intercept. We know that protons are made of quarks and gluons, in a most conventional collision this proton passes through each other without any reaction, but about 1 in a million collisions these protons hit each other so violently that it explodes and the collision energy is set free in this collision producing millions of new particles, the collision points are surrounded by detectors containing millions of sensors in them. They gather the data during this collision and send it to a computer, that computer creates an image with the data sensors sent to it. This data helps the scientist to study the nature of these particles and what they are made of.
Numerous researchers assume that dark matter particles are very light and therefore they can be created at LHC. If scientists are successful in creating these particles these particles would be able to escape through detectors unnoticed. However, using all the data like energy and momentum before the collision, scientists can notice the difference in energy and momentum since these dark matter particles will carry away energy while escaping.
Using all the data through numerous past experiments and forthcoming experiments we will be able to gather enough data to provide evidence for these particles.
Dark Matter is just simply what we call this thing about which we know nothing, responsible for practically 85% of the gravity of the cosmos. We’ve known about dark matter since 1930, yet, we are yet to discover the whole chapter about dark matter. We may think that humans have made so much excitement and great discovery and on the other hand, we know so little about our universe and how it works. The quest to find these answers is starting now, a new generation of technology making it possible to see millions and billions of light-years in space. These technologies and a new way of looking at our universe will assist us to answer some fundamental questions like who we are and what’s the nature of the universe, and what is the stuff that makes us who we are. With this technology and discoveries one day we will be able to see not only detectable things but also things that are invisible.
One day we will be able to reveal mysteries about the cosmos beyond what we could ever imagine. The new quest is looking for this hidden universe. From the time Galileo took a gander at the sky first time till now we’ve been looking for answers, a revolution in technology and race to search these answers has given us discoveries that have been revolutionary, earth-shattering, and profound. At each stage, we’ve pushed the boundaries of our universe a little further and further. Beyond our planet, past our galaxy and billions of galaxies like ours and basically back to the big bang, who can say for sure what we will discover later on.
