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What is Dark Matter in the Universe?

Dark matter is the mysterious stuff that fills up the universe but no one has ever seen. Over 80% of all matter in the universe is made up of a material scientists have never seen.

The unseen matter is called dark matter and we can only assume it exists because without it, the behaviour of stars, galaxies and planets wouldn’t make sense. 

Dark matter does not emit any light or energy and thus cannot be detected by conventional sensors or detectors. Visible matter (or baryonic matter) consists of baryons (subatomic particles like protons, neutrons and electrons). Most scientists think that dark matter is composed of non-baryonic matter. 

If we cannot see dark matter, how do we know it exists?

The answer is gravity. Since the 1920s, astronomers have believed that the universe must contain more matter than we see because the gravitational forces in the universe appear stronger than what the visible matter alone would account for.

“Motion of the stars tell you how much matter there is! They don’t care what form the matter is, they just tell you that it’s there”

Pieter Van Dokkum (Researcher at Yale University)

While studying spiral galaxies, astronomers expected to see the material in the center move faster than the outer edges. Instead, they found stars moving at the same velocities at both locations and even concluded that galaxies contained more mass than what could be seen.

In 2016, a team led by Van Dokkum found a galaxy called “Dragonfly 44” which seemed to be composed almost entirely of dark matter. Also in 2018, astronomers found several galaxies that seem to lack dark matter.

In the 20th century, Albert Einstein showed that massive objects in the universe bend and distort light due to the force of their gravity. This phenomenon is called Gravitational Lensing. By studying the distortion of light by galaxy clusters, astronomers have been able to map dark matter in the universe.

Dark Matter appears to be spread across the cosmos in a net-like pattern, with galaxy clusters forming at the nodes where fibers intersect. 

But where does dark matter come from?

We don’t know.

There are a few theories claiming to be the explanation of the existence of dark matter. A study published in December 2021 in the Astrophysical Journal argues that dark matter might be concentrated in black holes. It also states that dark matter would have been created in the Big Bang together with all the other elements of the universe.

An experiment module mounted on the International Space Station called the Alpha Magnetic Spectrometer (AMS) detects antimatter in cosmic rays. 

“We have measured an excess of positrons, and this excess can come from dark matter. But at this moment, we still need more data to make sure it is from dark matter and not from some strange astrophysics sources.”

Samuel Ting (AMS Lead Scientist)

Various telescopes orbiting Earth are hunting for the effects of dark matter. The ESA’s Planck Spacecraft (retired in 2013) spent four years at Lagrangian Point 2, mapping the distribution of the cosmic microwave background. Irregularities in the distribution of this microwave background revealed clues about the distribution of dark matter.

NASA’s Fermi Gamma-Ray Space Telescope made maps of the heart of our galaxy revealing an excess of gamma-ray emissions from its core.

“The signal we found cannot be explained by currently proposed alternatives and is in close agreement with the predictions of very simple dark matter models.” 

Dan Hopper (Astrophysicist at Fermilab, Illinois)

James Webb Space Telescope launched after 30 years of development, is also expected to contribute to the hunt for elusive substances.

Dark matter is one of the biggest mysteries in Astrophysics. And for more on such mysteries of the universe, Download the Volume app now, and subscribe to Space and Beyond.

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