Dark Matter and Dark Energy:

by Ananya Shah

Even though there’s a lot we can see, the majority of our universe is hidden from our sight. According to astronomers, our universe is primarily composed of mysterious, invisible “stuff” known as dark matter and dark energy.

Dark matter is known as an attractive force that keeps our universe together. Hence, it slows down the expansion of our universe. This is because dark matter does not reflect, absorb, or emit light, even though it does interact with gravity. On the other hand, dark energy acts as more of a repulsive force, a driving force to expand our universe as much as possible. It behaves almost as an “anti-gravity”, powering the universe’s accelerating expansion.

Though both of these forces are significant in nature, dark energy is, by far, the more dominant force, therefore yielding a net repulsive force causing our universe to expand. Of all the mass and energy of the universe, dark energy constitutes an astonishing 27%.

Now, how did these concepts come about? Thanks to the research done by several astronomers, the concepts of dark matter and dark energy have grown to become significant in society today.

The concept of dark matter originated in the 1930s, when a Swiss astronomer Fritz Zwicky studied images of the 1000 galaxies that comprised the Coma Cluster. However, he noticed something peculiar: the galaxies were moving so fast that they should fly apart, but they didn’t. Hence, he speculated that some kind of “dark matter” kept them together.

A similar pattern was spotted when astronomers Vera Rubin and Kent Ford studied the rotation speeds of individual galaxies. Generally, at the outer edge of a galaxy, the stars should rotate slower than the stars near the center, due to a weaker gravitational force. However, they instead observed that the peripheral stars orbit at the same rate - and maybe, even faster - as the stars closer to the center. Hence, Rubin and Ford proposed that some invisible form of matter was helping to hold the universe together, what is now known as dark matter.

Photo by Graham Holtshausen on Unsplash

Unfortunately, the identity of the scientist who first observed dark matter is unknown. However, the concept developed over time from telescopic observations showing that most galaxies are moving away from each other. This led to the idea of the Big Bang, though most astronomers presumed that the combined gravitational pull of all the cosmos’ stars and galaxies should be slowing down the universe. However, this was refuted when two teams of astronomers spotted distant galaxies moving away from us faster than nearby galaxies, therefore establishing that the universe wasn’t just expanding - it was speeding up as well. Since then, there have been many developments and places of uncertainty regarding dark matter and dark energy.

For example, on November 26, 2020, there was a very shocking discovery regarding missing dark matter in a galaxy, NGC 1052-DF4. The reason for this missing dark matter was uncovered by new Hubble data: tidal disruption. The gravity forces of a neighboring massive galaxy were tearing apart NGC 1052-DF4. As a result, the dark matter was removed, while stars feel the effects of galaxial interactions at a later stage.

So why is this important? Since dark matter and dark energy pertain to the expansion and contraction of the universe, understanding it is important to know our universe’s future. Since dark energy is the dominant force in nature, earth is constantly expanding at an increasing rate; at one point, dark energy density may grow to infinity, tearing apart all objects in the universe. That could be billions of years from now, or it may not even happen at all. However, only time will tell.

References

Betz, Eric. “What's the Difference between Dark Matter and Dark Energy?” Astronomy.com, 3 Mar. 2020, astronomy.com/news/2020/03/whats-the-difference-between-dark-matter-and-dark-energy#:~:text=And what's the difference between,dark energy speeds it up.&text=This is because dark matter,, absorb, or emit light.

“Dark Energy, Dark Matter.” NASA, NASA, science.nasa.gov/astrophysics/focus-areas/what-is-dark-energy.

“Home.” Science and Technology Facilities Council, stfc.ukri.org/news-events-and-publications/features/the-story-of-dark-matter/10-things-you-need-to-know-about-dark-matter/.

Information@eso.org. “New Hubble Data Explains Missing Dark Matter.” Www.spacetelescope.org, esahubble.org/news/heic2019/.