card
347

dark matter

OLogy Series
astronomy
card
347

dark matter

OLogy Series
astronomy

Most mass in the universe is not normal matter we can see, like stars, planets, and puppies. In fact, 80% of the mass is called dark matter. Invisible, it doesn't give off light like a galaxy or absorb light like a black hole. Scientists know it exists because it has a gravitational pull, just like normal matter. Astronomer Fritz Zwicky proposed this "cold, dark material" in the 1930s. He realized that galaxies must be held together by dark matter's gravity.

The gravity generated by dark matter is responsible for the grand structure of the universe. This structure is like the inside of a:

sponge

beach ball

bowling ball

Are you right?

Correct!

Dark matter's gravity creates the sponge-like structure of the universe. Some areas are dense with galaxy clusters, while others are cosmic voids -- big, empty bubbles, hundreds of millions of light years wide.

Today, scientists are trying to detect dark matter particles directly. These ultra-sensitive "detectors" are placed:

deep beneath Earth's surface

on the International Space Station

both of these

Are you right?

Correct!

In North America and Europe, detectors are buried deep underground, shielded from radiation from space. One detector is mounted on the International Space Station, where it looks for signs of dark-matter particles far from Earth.

Scientists can detect regions with lots of dark matter because they are very dark.

Fact
or
Fiction
?

Fiction

Dark matter doesn't interact with light in any way -- it doesnÂ’t give off light, but it doesn't absorb light either. Scientists can detect dark matter only by its effect on galaxies.

Like normal matter, dark matter is made of atoms.

Fact
or
Fiction
?

Fiction

Normal matter is made of protons, neutrons, and electrons. Scientists still haven't figured out what dark matter is made of but they know it's not atoms, which are detectable by light.

While the universe expands, galaxy clusters stay bound together: they don't expand.

Fact
or
Fiction
?

Fact

The cosmic space of universe is expanding, carrying clusters of galaxies with it. But galaxy clusters, and the galaxy they hold, stay together, bound by the gravity of dark matter.

Definition: an invisible substance that makes up 80% of the total mass in the universe
Detection: only by its gravitational influence on normal matter
Influence: its gravity holds together galaxies and galaxy clusters
Proposed: in 1930s by Fritz Zwicky
Confirmed: in 1978 by Vera Rubin. To explain the orbits of stars in spiral galaxies, she estimated that most matter in galaxies is invisible.