Everything scientists can observe in the universe, from people to planets, is made of matter. Matter is defined as any substance that has mass and occupies space. But there’s more to the universe than the matter we can see. Dark matter and dark energy are mysterious substances that affect and shape the cosmos, and scientists are still trying to figure them out.
The universe is made up of three components: normal or visible matter (5%), dark matter (27%), and dark energy (68%). NASA's Goddard Space Flight Center
Normal Matter
Normal matter makes up everything we can directly
observe. We can view it in visible light with our own eyes or through a
telescope that can detect light we can’t see, like ultraviolet or infrared.
Most normal matter is made up of atomic particles: protons, neutrons, and
electrons. It can exist as a gas, solid, liquid, or plasma of charged
particles. While normal matter is everywhere in our daily lives, it composes
less than 5% of the total universe.
Dark Matter
Like ordinary matter, dark matter takes up space and
holds mass. But it doesn’t reflect, absorb, or radiate light – at least not
enough for us to detect yet.
While scientists have measured that dark matter makes
up about 27% of the cosmos, they’re not sure what it is. Theories include
several kinds of as-yet unidentified types of particles that rarely interact
with normal matter.
NASA's Hubble Space Telescope captured the magnificent starry population of the Coma galaxy cluster, one of the densest-known galaxy collections. The view, spanning several million light-years across, covers a large portion near the cluster’s center. NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Astronomers didn’t even know dark matter existed until
the 20th century. In the 1930s, Swiss astronomer Fritz Zwicky coined the term
while studying the Coma galaxy cluster, which contains more than 1,000
galaxies. The speed at which galaxies within a galaxy cluster move depends on
the cluster’s total mass and size. Zwicky noticed that galaxies in the Coma
cluster were moving faster than could be explained by the amount of matter
astronomers could see there.
It wasn’t until the 1970s that U.S. astronomer Vera
Rubin confirmed the existence of dark matter by studying how individual
galaxies rotated. She and her colleagues found that individual galaxies may
contain invisible mass made of dark matter.
Scientists today think dark matter exists in a vast, web-like structure that winds through the whole universe – a gravitational scaffold that attracts most of the cosmos’ normal matter. They’ve determined that dark matter isn’t composed of known particles of matter because the universe would look very different if it were. The search for what makes up dark matter continues.
Source: Building Blocks - NASA Science
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