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What is Dark Matter? – A Brief Introduction

Dark Matter

We had studied in school that Everything around us is made up of matter but it’s not completely true. You will be surprised to know that only 4% of the universe is made up of ordinary matter which is visible to us. The rest of the universe is filled with invisible and mysterious constituents known as dark matter and dark energy.

Prediction of dark matter and dark energy was a groundbreaking idea. Scientists haven’t seen dark matter yet but they had detected indirectly. Many surprising observations were made due to the presence of dark matter. Let’s dive into the ocean of exotic dark matter.


History and Background

It is almost impossible to detect dark matter with current instruments. In the 20th century, astronomer observed the weird behavior of many galaxies and clusters of galaxies. It is expected that stars present in the outer region of a galaxy should travel slower as compared to stars present near the center.


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(Image Credits: Max Planck Institute for Astrophysics)


But this wasn’t the case as the stars present near the center as well as at the outer region traveling at an almost similar speed. This could happen if galaxies have an enormous mass than what is seen. This invariance is so high that Scientists predicted that there must have a hundred times more dark matter than ordinary Baryonic matter.

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DID YOU KNOW? – Baryonic matter is referred to as normal matter which consists of proton and neutron.


Expanding Universe

Till the 1990s, physicists assumed that due to gravitational force, expansion of the Universe would slow down over time. But the reality was different. When 2 teams tried to find out deceleration but they found that the universe is expanding with increasing speed.

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(Image Credit: NASA/EAS)


Scientists suggested that there should be some repulsive force that exists and that is dark matter, but the astrophysicist doesn’t have any strong explanation for dark matter. They know that dark matter surely exists. Many observable outcomes are seen due to dark matter.

Related | Neutrinos: A Key to Understand Our Universe

Gravitational Lensing


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(Image Credits: Rubin Observatory)


When light from a distant Galaxy is distorted and magnified by massive clouds of dark matter then some strange rings are seen. As light travels it carries some information about galaxies. This can be a great way to study distant galaxies and enormous mass is necessary to see such observations, and scientist believes that dark matter has such a huge mass.

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For now, it’s not possible to detect dark matter directly, but there are some possible ways from which the study of dark matter is possible. If dark matter is made up of subatomic particles then thousands of particles must pass through earth each second.

Many experiments are carrying out to test this hypothesis. WIMPS (weakly interacting massive particles) and AXIONS are popular candidates to solve the mystery of dark matter. The detection of dark matter can be further categorized into direct and indirect detection.

Direct Detection

In the direct detection method, it is expected that when dark matter particles pass thought detector, it will produce low-energy recoil of nuclei. After recoil energy is emitted in the form of scintillation light. Generally, cosmic rays can interfere with the results. therefore, these experiments are carried out deep underground.

These experiments mostly use cryogenic or Nobel liquid detectors. Since the cryogenic detector is operating at a very low temperature, it detects a small change in temperature produced by the particle when it hits the atoms. Nobel liquid detects scintillation produced by a particle in liquid xenon or liquid argon.


Indirect Detection

Its indirect detection, which involves the search for the production of the annihilation of particles. If dark matter particles could annihilate to form a standard model particle or dark matter particle then it could be a great way to detect dark matter. There is a strong possibility that cosmic rays and other sources could interfere with the observable result. Hence it is necessary to take out some way to eliminate those disturbances.

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(Image Credits: Alex Geringer-Sameth, Matthew G. Walker, Savvas M. Koushiappas, et. / Carnegie Mellon University)


Scientists also speculated that when dark matter particles pass through the sun may scatter off atoms due to which it will lose energy. Thus, it would accumulate near the center and this would lead to some signal in the form of high energy neutrino. This signals would be strong evidence of WIMP dark matter. Many detectors such as AMANDA, IceCube, and ANTARES are searching for this signal. Also, scientists believe that gravitational waves could be a way to understand dark matter. Gamma-ray emissions are a possible way to detect dark matter.

It may seem like dark matter is really dark to understand, but we would hope that very soon we will be able to understand everything about dark matter. Till then happy reading and happy asking why?


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