Dark matter

Space has a big secret.

Most of it is hidden. We cannot see it. It does not use light. But it pulls on things.

This pulling is called gravity. It acts like a net. It holds big groups of stars together. Without this pull, stars would fly away.

Scientists think this hidden stuff is everywhere. It helps make the shape of the universe. It even helps make big webs of stars.

Most of the stuff in space is not like us. Only a tiny part is the normal stuff we see. The rest is this hidden mass.

We do not know what it is yet. It might be tiny bits we cannot find. It is a great mystery to solve!

Space has a big secret. It is filled with something called dark matter.

We cannot see dark matter. It does not use light. It does not give off any light at all. This makes it very hard to find. Scientists know it is there because of gravity. Gravity is a pull that happens when things have mass.

Dark matter acts like a frame for the universe. It helps build big structures like galaxies. After the Big Bang, it formed long strands. These strands made a cosmic web. Galaxies sit on this web like tiny dots.

Most of the universe is not what we see. Only 5% is normal matter. Dark matter makes up 26.8% of the universe. The rest is dark energy. Dark matter is 85% of all mass.

What is it made of? Many think it is a tiny particle. They call these WIMPs. WIMPs are particles that are hard to catch. Others think it might be small black holes. We are still searching for the truth.

Space holds a huge mystery called dark matter. We cannot see it because it does not interact with light. This means it does not reflect or give off any light. Scientists call it invisible and hypothetical. They know it exists because of how it pulls on other things. This pull is called gravity.

Without this extra gravity, galaxies would not stay together. Dark matter acts like a cosmic scaffolding for the universe. After the Big Bang, it clumped into long strands. These strands created a cosmic web. Galaxies sit on this web like tiny particles.

How does dark matter work in space? It works through its gravitational effect. It pulls on visible stars and gas. This pull helps form and change galaxies over time. We can see it through gravitational lensing. This is when gravity bends light from distant objects. It also affects how galaxy clusters move.

Scientists also see its effects in the cosmic microwave background. This is the leftover heat from the start of the universe. Dark matter helps decide the structure of everything we see. It is a key part of how the universe grows.

People have studied this mystery for a long time. In 1884, Lord Kelvin talked about dark bodies near the Sun. In 1906, Henri Poincaré used the term "dark matter." Later, astronomers like Jacobus Kapteyn and Knut Lundmark shared ideas about unseen mass. In 1933, Fritz Zwicky studied the Coma Cluster at Caltech. He found that galaxies moved much too fast. He thought unseen mass must be holding them together.

Zwicky was right about the hidden mass. In the 1970s, Vera Rubin and Kent Ford found more proof. They looked at how spiral galaxies rotate.

There are many important numbers to know about the universe. Ordinary matter makes up only 5% of the mass-energy content. Dark matter makes up 26.8% of the universe. The rest, 68.2%, is a form of energy called dark energy. This means dark matter is 85% of all the mass.

In our own Solar System, dark matter is hard to find. Near Neptune, the dark matter weighs about 10 to the 17th kg. That is about the same as a large asteroid. Most scientists think dark matter is made of tiny particles. They call these WIMPs or axions.

Dark matter is like an invisible glue for the stars. You can think of it like a hidden wind. You cannot see the wind, but you see the trees move. In space, we cannot see dark matter, but we see galaxies move.

Some people think we need to change our laws of gravity instead. They study ideas like modified Newtonian dynamics, or MOND. However, most scientists still look for new particles. Experiments like LZ use liquid xenon to find them.

We are still learning how this invisible part of our world works.

Dark matter is an invisible and hypothetical form of matter. It is a major mystery in astronomy and cosmology. Scientists cannot see it because it does not interact with light. It does not emit, absorb, or reflect electromagnetic radiation. We know it exists because of its gravitational effects. These effects cannot be explained by general relativity alone. Without dark matter, there would not be enough visible matter to explain how the universe works.

Dark matter acts as a gravitational scaffolding for the entire universe. After the Big Bang, dark matter clumped into large blobs. These blobs formed narrow filaments across space. These filaments created a cosmic web. Entire galaxies appear like tiny particles sitting on this web. Dark matter helps drive the formation and evolution of galaxies. It also influences the current structure of the observable universe.

We can observe dark matter through several specific mechanisms. One method is gravitational lensing. This occurs when the gravity of a massive object bends light from a distant source. Another way is by watching galaxy clusters. We can see how galaxies move within these large groups. Dark matter also affects the cosmic microwave background. These are tiny temperature variations left over from the early universe.

Scientists classify dark matter based on its velocity. They use terms like "cold," "warm," or "hot" dark matter. This classification depends on the free streaming length of the particles. Most recent models favor a cold dark matter scenario. In this scenario, cosmic structures emerge through the gradual accumulation of particles. This process helps build the large structures we see today.

The history of this discovery spans over a century. In 1884, Lord Kelvin suggested there might be many dark bodies near the Sun. In 1906, Henri Poincaré used the term "dark matter" to describe these ideas. In 1933, Fritz Zwicky studied the Coma Cluster at Caltech. He used the virial theorem to study galaxy motions. Zwicky found that the cluster had 400 times more mass than was visible. He concluded that unseen mass provided the necessary gravitational attraction.

In the 1970s, the hypothesis of dark matter became widely accepted. Astronomers like Vera Rubin and Kent Ford studied galaxy rotation curves. They used new spectrographs to measure how spiral galaxies rotate. They found that galaxies rotate much faster than visible stars should allow. This suggested that galaxies are surrounded by large halos of dark matter. Other researchers used radio astronomy to map hydrogen gas. This provided even more evidence of these invisible halos.

The composition of the universe is dominated by these invisible components. Ordinary baryonic matter makes up only 5% of the mass-energy content. Dark matter accounts for 26.8% of the total content. The remaining 68.2% is a form of energy called dark energy. This means dark matter represents 85% of the total mass in the universe. However, dark matter is very sparse in our local area. The total dark matter out to Neptune's orbit is only about 10^17 kg. This is roughly the mass of a large asteroid.

Researchers are currently searching for the identity of dark matter particles. The most popular theory involves weakly interacting massive particles, or WIMPs. Another strong candidate is the axion, a very light particle. Some scientists even suggest dark matter could be primordial black holes. Large experiments like LZ use liquid xenon to try to detect WIMPs. So far, these direct detection experiments have only reported null results. This has caused some scientists to look closer at alternative theories.

Some astrophysicists propose that we do not need dark matter at all. They argue we might need to modify the laws of gravity. These theories include modified Newtonian dynamics, known as MOND. Other ideas include tensor-vector-scalar gravity and entropic gravity. However, these modified gravity theories struggle to explain all observations. Most evidence suggests that some form of dark matter is still required. The search for the truth continues through new technology and observation.