Everything we can see like planets, stars, and galaxies makes up only a small fraction of the universe i.e. less than 15% and the other 85% of the universe is invisible and scientists call this hidden substance dark matter.
What is Dark Matter?
Matter is anything that has mass and occupies space. Black matter is the matter which does not absorb, emit or reflect light and is completely black. You all may have observed that all the images of the universe made by the astronomers are always fully black except the stars and planets it is because that dominating black part is the black matter. Black matter is actually an invisible glue which holds the universe together.
This mysterious material is all around us making up 85% of the total universe. Although dark matter interacts with the ordinary matter through gravity but it does not seem to interact at all with the electromagnetic spectrum including the visible light. Scientists have been trying for more than 100 years to solve this mystery that what exactly is black matter.
What does it mean by Invisible Universe?
The universe is not only made of stars and planets. All the visible matter (like gas, dust, planets, and stars) adds up to only 15% of the total universe and the rest of the 85% of the universe which is composed of dark matter is called invisible universe because it is like an invisible glue that holds the whole universe together.
The dark matter is invisible but being matter it does have some things in common with ordinary matter. It takes up space and it holds mass. Because of this, we can see how it interacts with and influences ordinary matter throughout the universe, this is how we’re able to identify and study dark matter.
How do scientists know Dark Matter exists?
As the dark matter is invisible so how would have scientists detected it’s presence? The answer to this question is really simple, scientists detect its presence through it’s gravitational effects:
Cosmic Microwave Background (CMB) – Ancient radiation left from the Big Bang shows patterns that suggest dark matter exists.
Galaxy Rotation Mystery – Galaxies spin so fast that they should fly apart but they don’t so something unseen holds them together.
Gravitational Lensing – Light bends around massive invisible structures showing dark matter’s presence.
Possible Building Blocks of Dark Matter
There is no confirmed information about what dark matter is made off. Scientists don’t know yet but following are the some theories and possibilities about what the components and building blocks of dark matter could be:
WIMPs (Weakly Interacting Massive Particles): Hypothetical particles that could form dark matter.
Axions: Ultra-light particles that may exist throughout space.
MACHOs (Massive Compact Halo Objects): Black holes, neutron stars or faint old stars that could make up some part of it.
Discovery of Black Matter
It might sound impossible that how can someone discover something which can’t be seen? This is the question which scientists have been trying to figure out since 1930s. During that time, astronomers noticed something unusual in galaxies. They observed that there seemed to be a “missing matter.”
The phrase “Dark Matter” had popped up before but it was in 1933 that a Swiss astronomer Fritz Zwicky gave the idea real weight. While studying the Coma Cluster, he realized a group of galaxies were moving far too quickly as compared to the amount of visible matter they contained. According the laws of gravity, those galaxies would have flown apart but they stayed together. Fritz Zwicky proposed that some sort of invisible material was providing the extra gravity. He called it “Dunkle Materie”. It is a German phrase which means “Dark Matter” in English.
Most of the scientists weren’t convinced as the idea sounded like a science fiction. But things changed in the 1970s when an American astronomer Vera Rubin made a groundbreaking discovery. While studying spiral galaxies she found that the stars at the extreme edges were moving just as fast as the ones near the center. Normally, those outer stars should have been flung into deep space. The fact that they stayed in orbit mean that there had to be an enormous amount of hidden mass keeping them in place. Vera Rubin said that this mysterious mass was none other than dark matter.
Her findings were so strong that the scientific community could no longer ignore the idea. What started as a fringe theory in the 1930s had now become one of the biggest puzzles in modern astronomy. Even today, scientists still don’t know what dark matter is made of but most of them are agreed upon it’s existence that it have been silently shaped the universe and is holding galaxies together like an invisible glue.
How Colliding Galaxies Revealed Dark Matter
Scientists today have much stronger evidence that dark matter is real and it is not a science fiction. Even though it doesn’t interact with light, its gravity bends light from distant galaxies. This strange effect is called gravitational lensing. The astronomers see the influence of dark matter even if they can’t see the matter itself. By studying the way galaxies look stretched or distorted by this effect, scientists can learn more about how dark matter shapes the universe.
One of the most famous examples is a gigantic collection of galaxies called the Bullet Cluster, located about 3.8 billion light-years away. This massive system was formed when two huge galaxy clusters violently collided. The event produced an incredible cosmic laboratory for scientists to study dark matter.
During the collision, the hot gas from each cluster slammed into each other, producing powerful X-rays that NASA’s Chandra X-ray Observatory detected. In images, this glowing hot gas appears pink. But here’s the surprising part is that the gravitational lensing revealed that most of the mass in the Bullet Cluster was not in the pink gas. Instead, it showed up as vast patches of blue which represents dark matter.
In other words, the normal matter (the hot gas and visible galaxies) and the dark matter ended up in different places after the collision. This separation gave scientists the clearest and most direct evidence that dark matter truly exists. It was no longer just a theory as it was something we could actually map.
Today, researchers continue to build dark matter maps to figure out where this mysterious stuff is actually hiding across the universe. Upcoming missions like NASA’s Nancy Grace Roman Space Telescope will allow astronomers to chart the distribution of dark matter with incredible precision.
Why are the scientists so interested in studying Dark Matter? Because dark matter acts like the invisible glue of the universe. Understanding how it’s spread out will help answering some of the biggest questions of science like: “How is the universe structured”? and “How has it changed over billions of years”?
Temperature of Dark Matter: Is it Hot or Cold?
As Dark Matter has mass then it must have a temperature too but here’s the question is that will it be hot or cold? Scientists have argued back and forth for years about this. If dark matter is composed of slow-moving particles then it would be cold dark matter. If it is composed of fast-moving particles then it would be warm or hot dark matter.
To try out these ideas, scientists simulated the universe using computers. They contrasted what galaxies and cosmic structures would be like in each case. The outcome was obvious that it would be cold dark matter because the simulations coordinated with what we see in the universe really exist i.e. galaxies colliding, remaining intact and living up to expectations. But with hot or warm dark matter, it is all disintegrated, the cosmic structures did not hold together and the universe within those models was not like our own.
Most of the scientists today believe that dark matter is cold and slow-moving. They also believe that this cold dark matter existed in the earliest universe and moved slowly enough to give rise to galaxies that then spread out into the things we see today.
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