Studies and Theories on Dark Matter Particles

From the Lecture Series: Great Heroes and Discoveries of Astronomy.

By Emily LevesqueUniversity of Washington

Despite Vera Rubin’s effort in spotting dark matter, we still don’t know what dark matter is actually made of. Nobody has ever detected a dark matter particle; we’re not even sure dark matter is a particle, although most astrophysicists today believe that an as-yet-undiscovered subatomic particle is the most likely explanation for what dark matter is made of.

Deep space with stars and galaxies; concept of the universe
The discovery of dark matter changed the understanding of how the whole universe works. (Image: Antrakt2/Shutterstock)

Recognizing Vera Rubin’s Work

It seems impossible to ignore the enormous impact that Vera Rubin’s discovery of dark matter has had on the world of science, and organizations all over the world have agreed. For her work, she was awarded the National Medal of Science in 1993, an honor bestowed by the president of the United States to those who have made vital contributions to the sciences. 

Her research received the James Craig Watson Medal from the National Academy of Sciences, the Gruber Cosmology Prize, and the Dickson Prize in Science. She received the Gold Medal of the Royal Astronomical Society, the Henry Norris Russell Lectureship from the American Astronomical Society, and numerous other lifetime achievement awards. She also earned the Richtmyer Memorial Award, a prestigious award recognizing outstanding physics education in the United States that includes more than a dozen Nobel laureates among its recipients.

Subatomic particles in a dark background
Vera Rubin’s discovery of the dark matter is one of the most groundbreaking discoveries in physics in the 20th century (Image: Ezume Images/Shutterstock)

More Recognition for Vera Rubin

Rubin passed away in 2016.  As a result, the venerated Nobel Prize in Physics, which cannot be awarded posthumously and was not awarded to Rubin during her lifetime despite her immense contribution to the field, now permanently lacks any recognition of one of the most groundbreaking discoveries in physics in the 20th century.

Today, Vera Rubin has a prize of her own—the Vera Rubin Early Career Prize is awarded annually by the American Astronomical Society’s Division on Dynamical Astronomy, a division specifically devoted to studying the dynamics and motions of stars and galaxies. 

And a new observatory in the Andean foothills of Chile, the Large Synoptic Survey Telescope, built to repeatedly survey the entire Southern Sky and study new mysteries of the universe, has been renamed the Vera C. Rubin Observatory. She is the first woman to have a national US observatory named after her.

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Massive Compact Halo Objects Theory or MACHO

After Vera Rubin’s discovery of dark matter, physicists and astronomers all over the world continued studying in the hopes of learning more about how this matter works and what it’s made of. For a long time, two competing theories for dark matter were MACHOs and WIMPs.

They sound like ridiculous names, but they’re really just slightly silly acronyms. MACHOs stands for massive compact halo objects and refers to the idea that dark matter could be explained by dark sorts of objects: heaps of black holes, old cold stars, and other objects, massive and compact and hanging out in the halos around galaxies.

However, most evidence does not favor MACHOs as an explanation. If dark matter could be explained by big, dark, compact objects, we would expect to see tiny amounts of gravitational lensing from these individual objects and their particles, and so far, no observations have seen these effects.

The cosmic microwave background also strongly suggests that dark matter is made up of matter particles that don’t interact with light at all—it’s truly invisible, rather than just dark, as the MACHOs theory would suggest.

WIMP: Weakly Interacting Massive Particles Theory

What about WIMPs? WIMPs stands for weakly interacting massive particles. This theory, and other related particle physics theories, are where most current research on dark matter is focused. Most theories predict that dark matter could be made of some new elementary particle that simply hasn’t been observed yet. 

Conceptual image of dark matter
The nature of dark matter is still a mystery for scientists and astronomers. (Image: Sakkmesterke/Shutterstock)

Many different research groups are actively engaged in pursuits to find signs of dark matter particles, hoping to directly observe signs of dark matter particles interacting with other particles or even with each other. Every day, these experiments make progress in understanding how dark matter could work and what it might be, but so far nobody has conclusively detected signs of dark matter particles. 

We’ve learned a great deal about how dark matter works, and what it does to its surroundings, but when it comes to answering the question of what dark matter actually is, we still don’t know. What we do know is that dark matter has had an immense influence on physics and astronomy. 

It has changed our understanding of how galaxies work, shaped our current explanation for how the cosmos has evolved, and spawned an entirely new subfield and numerous observational and laboratory experiments dedicated to understanding this mysterious phenomenon.

Common Questions about Studies and Theories on Dark Matter Particles

Q: What does MACHOs stand for?

It is a theory about the nature of dark matter. MACHO is an acronym for massive compact halo objects. It refers to the idea that dark matter could simply be a variety of dark objects hanging in halos around galaxies.

Q: What does WIMPs stand for?

WIMPs stands for weakly interacting massive particles. Most research on dark matter has focused on this and other theories related to particle physics. Theories such as WIMPs predict that dark matter may be composed of elementary particles that have simply not been discovered yet by researchers.

Q: Do we know what dark matter is made of?

Researchers and scientists have learned a lot about how dark matter works and what it does to its surroundings. But when it comes to answering the question of what dark matter really is and what it is made of, everything seems uncertain. It seems that dark matter particles have not been determined by anyone yet.

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