What is Dark Matter?
Being a science enthusiast, you may have come across the word dark matter, or maybe you already have a theory of your own. Well, let’s take a deeper dive into the dark matter, and let’s find out what is dark about it. Dark matter may be defined as a form of matter considered to be approximately 95 percent of the matter of the universe. After several scientific studies, it is assumed that dark matters are about 27% of its total mass-energy density or about 2.241×10−27 kg/m3. In this article, we are going to discuss dark matter theory, the meaning, and its discovery in detail.
The Discovery
The existence of the ‘missing mass’ or ‘dark matter’ was first proposed by Swiss American astronomer Fritz Zwicky. In 1933, he discovered that only 1 percent of the mass of all the stars in the Coma cluster is needed to keep the galaxies from escaping the gravitational pull of the cluster. In the 1970s, this theory was approved upon observations by American astronomers, Vera Rubin and W. Kent Ford. They observed, within a galaxy, the mass of the visible stars is only about 10 percent that is required to keep the stars orbiting the center of the galaxy. To account for the slightly increasing (or constant) orbital velocity of the stars, the mass of the galaxy within the orbit of the star must be increasing linearly with the distance of the center of the galaxy from the stars.
Dark Matter Meaning
There are several observations to imply the presence of dark matter such as gravitational effects. Until and unless more matter is present beyond our observations, they are not explained by accepted theories of gravity. Dark matters are substances that do not absorb, reflect or emit light and hence not visible. Dark matter is a non-interacting substance, and this is what makes it dark and mysterious. It is considered that about 5 percent of the universe is known to us. The rest 95 percent includes about 27 percent of dark matter and 68 percent of dark energy. We are pretty sure of the existence of dark matter, but still to find out what dark matter is and how it exactly works.
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Dark Matter Theory
The existence of dark matter can be confirmed upon the discoveries of Swiss American astronomer Fritz Zwicky and Jan Oort. According to them, the motion of the galaxies and nearby stars of the Coma clusters violates the expected motions according to Newton's law of gravity. But still, any direct evidence of the presence of the dark matter is not encountered.
According to NASA, we know more about what a dark matter isn’t than what it is. Dark matter cannot be seen in the form of our known cosmic objects such as stars and planets. It is not in the form of baryons as we know we would be able to detect baryonic clouds by their absorption of radiation passing through them. Again, dark matter is not antimatter, because we do not see the unique gamma rays that are produced when antimatter collides with another matter. Based on how many gravitational lenses we see, we can rule out large galaxy-sized black holes. High concentrations of matter cause the bending of light, which passes near them from objects further away. But we cannot see enough lensing events so that it can suggest that such objects have the required 25% contribution of dark matter. There must be several theories about the existence of dark matter, but no direct evidence is acquired till now.
Did You Know?
Dark matter is a subject that gives us goosebumps, thinking about the fact that it is yet to be discovered. The Discovery of dark matter and dark energy would give us a better picture of the universe and how it exactly works. Here are some facts about dark matter. The substance of dark matter doesn't interact with light and that is why dark matter is invisible. Though dark matter cannot be seen, it can be felt for its powerful cosmic impact. It is predicted that the powerful impact of dark matter binds the galaxies together. According to some research, dark matter might be cold in nature. Also, dark matter might not have any existence.
FAQs on Dark Matter
1. What is dark matter in simple terms?
In simple terms, dark matter is a mysterious, invisible substance that is thought to make up about 27% of the universe. It does not emit, absorb, or reflect any light, which is why it's called 'dark'. We can't see it directly, but we know it exists because of the gravitational pull it exerts on the visible matter we can see, like stars and galaxies. Think of it as the invisible cosmic scaffolding that holds galaxies together.
2. Who first proposed the idea of dark matter?
The idea of 'missing mass' was first proposed by Swiss astronomer Fritz Zwicky in the 1930s. While studying the Coma Cluster of galaxies, he observed that the galaxies were moving too fast to be held together by the gravity of their visible stars alone. Later, in the 1970s, astronomers Vera Rubin and W. Kent Ford provided stronger evidence with their studies of galaxy rotation curves, confirming that an unseen mass was required to explain their observations.
3. What is the main evidence for the existence of dark matter?
While dark matter has not been directly detected, its existence is supported by several independent lines of strong astronomical evidence. The main proofs include:
- Galaxy Rotation Curves: Stars at the outer edges of galaxies orbit just as fast as stars near the centre, which defies the laws of gravity unless a large halo of unseen matter is providing extra gravitational pull.
- Gravitational Lensing: The gravity of massive galaxy clusters bends light from objects behind them. The amount of bending observed is far greater than what the visible matter can account for, implying the presence of significant dark matter.
- Cosmic Microwave Background (CMB): The patterns seen in the leftover radiation from the Big Bang perfectly match theoretical models of a universe that includes the amount of dark matter we currently estimate.
4. How is dark matter different from dark energy?
Although their names sound similar, dark matter and dark energy are two completely different and opposing concepts. Dark matter is a form of matter that exerts a gravitational pull, attracting and holding galaxies and galaxy clusters together. In contrast, dark energy is a property of space itself that causes the accelerated expansion of the universe, acting as a repulsive force that pushes everything apart.
5. Is there dark matter on Earth or in our solar system?
Yes, scientists believe that particles of dark matter are constantly passing through our solar system, the Earth, and even our bodies. However, because dark matter interacts so weakly with normal matter, its presence is completely unnoticeable in our daily lives. Its effects are only significant on a massive, galactic scale where its collective gravity becomes a dominant force.
6. Why is dark matter considered 'dark' if it has mass and gravity?
The term 'dark' does not mean it is black or has a colour; it means it is transparent to light. Dark matter gets its name because it does not interact with the electromagnetic force. This means it does not absorb, reflect, or emit any form of electromagnetic radiation, including visible light, X-rays, or radio waves. Its existence can only be inferred through its gravitational effects on the visible universe, not by seeing it directly with any kind of telescope.
7. What are the leading theories about what dark matter could be made of?
The exact nature of dark matter is one of the biggest unsolved mysteries in physics. However, scientists have several leading candidates for what it could be:
- WIMPs (Weakly Interacting Massive Particles): These are hypothetical, heavy particles that are thought to interact only through gravity and the weak nuclear force, making them extremely difficult to detect.
- Axions: These are other hypothetical particles that are extremely light and do not interact strongly with normal matter.
- Sterile Neutrinos: A hypothesised fourth type of neutrino that would interact with other matter only through gravity.
Experiments around the world are currently underway to try and detect these particles and solve the mystery.
