The 9 biggest unanswered questions about dark matter

Dark matter is like a puzzle, but it could play a very important role in our understanding of the universe.

The issues surrounding the dark matter are some of the most important physical mysteries of our modern age. The existence of dark matter was originally proposed by the Dutch astronomer Jacobus Kapteyn in 1922, using research on stellar velocities. Then, in 1933, Fritz Zwicky noticed something strange in the distant cluster of Coma galaxies.

The Swiss-American astronomer has discovered that the mass of all-stars in the Coma galaxy cluster provides only about 1% of the mass needed to prevent galaxies from escaping the gravitational pull of the cluster.

In fact, dark matter was originally called “missing matter” because astronomers could not find it by observing the universe using any part of the electromagnetic spectrum.

It was not until the 1970s that dark matter was officially confirmed by American astronomers Vera Rubin and W. Kent Ford.

So what is the current hype surrounding dark matter? You may have seen it in science fiction movies or TV shows or even read about it in the news as the scientific community tries to understand it better.

Understanding this missing material could help scientists better understand the precise nature of the universe and perhaps even the end of our universe.
According to some theories, dark matter is much more widespread than we think.

The amount of dark matter could tell us if the universe is expanding, or if it could collapse in the distant future, or stop moving altogether. Dark matter could also help researchers better understand how gravity works or how galaxies form.

The list goes on. However, there are still many unanswered questions about dark matter that need to be addressed before astronomers can move forward. Today is what we are going to explore. Let’s start.



1. What exactly is dark matter?

What exactly is dark matter?

If you are still not sure what dark matter is, you are not alone. Although many researchers believe that dark matter represents 85% of the matter in the universe, there is still no agreement on what exactly dark matter is.

Also, the more we study dark matter, the more cloudy things seem. However, there are two main theories regarding the nature of dark matter.

One is that dark matter is made up of ordinary but hard-to-see dead stars or huge cold planetary objects. These objects would accumulate inside galaxies in a “halo” and are therefore called “Massive Compact Halo Objects”, or MACHO.

The other popular theory is that dark matter is made up of undiscovered particles that were created during the Big Bang and exist everywhere. These are called Weakly interacting Massive Particles or WIMP. This is currently the main theory.

Fermilab physicist Don Lincoln of the United States Department of Energy developed this idea in his article for Livescience, declaring: “We have never observed dark matter directly, but we know a lot about what it should be. : it must be massive (because it affects the rotation of galaxies); it must be electrically neutral (because we cannot see it); it must be different from ordinary matter (because we see no evidence of its interaction with matter in the usual way), and it must be stable (since it has existed since the dawn of the universe.) These properties are unequivocal. “

“However, we don’t know exactly what it is. In the most popular generic theory, the dark matter particle is called WIMP, for massive particles that interact weakly.

WIMP is a bit like heavy neutrons (but certainly not neutrons), with a mass of 10 to 100 times heavier than a proton. They were created in large quantities during the Big Bang, and a small relic still remains today. ”

However, even if these WIMPs are barely detectable, they should be everywhere and we should be able to interact with them in one way or another.

This was the dominant theory for a long period of time. Over the decades, researchers have built machines to detect WIMP dark matter particles to no avail until recently.

A dark matter detector in Italy recently returned with positive results. However, the DAMA experiment is very controversial, like other dark matter detectors in the world, offering contradictory results. For the moment, we do not yet have definitive proof that these theoretical particles even exist.



2. Does dark matter interact with something?

Shouldn't dark matter interact with something?

Absolutely yes. But it’s much more difficult than you might think. First, researchers can only study dark matter by seeing how it affects the universe around it. So far, the only thing that has been observed is the gravitational effects of dark matter, which still obscure our ideas on the subject.

From previous studies on the phenomenon of dark matter, we know that it affects celestial objects. But what if the dark matter is not a particle? Maybe it’s a field? Or maybe we don’t fully understand how gravity works.

In 2015, researchers observed four large clusters of what they believed to be dark matter surrounding four colliding galaxies. Their observations showed one of the clusters strangely behind its galaxy.

Not only does this seem to confirm that dark matter affects galaxies, but it also demonstrates that dark matter can interact with other dark matter. However, we still have to see if dark matter interacts with ordinary matter.



3. Can we study dark matter properly?

Can we study dark matter properly?

As mentioned above, the researchers have been trying to detect dark matter particles for years, without success. However, if the WIMP theory is correct, it would be very difficult to measure them correctly.

Yet, if we assume that these particles are traveling in space, at some point, dark matter should interact with a more familiar form of ordinary matter, such as a proton or an electron.

To measure this, researchers have built experiment after experiment to study the interactions of ordinary particles deep underground, where they are protected from stray radiation that could mimic a dark matter-particle collision.

However, even the most recent Chinese PandaX experiment has yet to produce conclusive results. A prevailing theory to explain this is that dark matter particles are actually much smaller than WIMP and therefore very difficult to detect.



4. Could dark matter be made of more than one particle?

Could dark matter be made of more than one particle?

This question makes a lot of sense. After all, ordinary matter is not just made up of protons and electrons. It also contains a multitude of “exotic” particles such as neutrinos, muons, and pions.

It would not be too far off to believe that dark matter has a similar “exotic” mixture of particles. “The particles of dark matter are essentially made up of heavy” black protons “and” light “black electrons”, explains Charles Q. Choi.

“They would interact much more than other dark matter particles to form” dark atoms “which use” dark photons “to interact through a kind of” dark electromagnetism “, just like protons and regular electrons interact through the photons to build up the atoms that make up the stuff of everyday life.

If dark atoms are possible, they could react with each other for dark chemistry, just like regular atoms interact chemically. “



5. What are dark forces?

What are dark forces?

No, we are not talking about the dark side of the Force. Still, it could work the same for what we know. As mentioned above, dark matter can be made up of so-called black particles.

The way dark protons and dark electrons interact could explain why dark matter clumps together, forming spherical halos around galaxies, stars, and planets.

It could also open the possibility of the existence of dark photons. What are dark photons, you ask?

In short, these are photons exchanged between normal particles which give rise to the electromagnetic force, except that they would only be felt by particles of dark matter. Such theories could open a Pandora’s box on a whole other side to the universe.



6. What if dark matter is the matter of axioms?

What if dark matter is the matter of axioms?

While some researchers continue to focus on WIMP theory, the search for weak particles has paid attention to another particle, the axioms.

These are ultra-light particles, billions of times lighter than the electron. They are considered by some to be an excellent candidate for dark matter, for many reasons.

First of all, their invisible presence would explain why the universe is much heavier than it seems. Second, the particle would also show why the two fundamental forces that shape atomic nuclei follow different rule books.

The Axion Dark Matter Experiment(ADMX) at the University of Washington is currently leading the charge for axiom and dark matter science.

The axion is a candidate for dark matter because, like dark matter, it cannot really interact with ordinary matter. This distance also makes the axion, if it exists, extremely difficult to detect.

This strange particle could also help solve a long-standing conundrum in physics known as the “strong CP problem”.



7. Does the ‘dark matter’ exist in every galaxy?

Does the 'dark matter' exist in every galaxy? 

One of the main theories about dark matter is that it plays a vital role in the formation of galaxies.

Dark matter is believed to play a role in controlling and organizing the formation of large celestial structures. However, researchers have now found a galaxy that appears to have no dark matter at all.

If we consider the dark matter as the scaffolding that holds the universe together, why would a galaxy miss these crucial structures?

One answer is that dark matter may not play as important a role in the formation of celestial bodies as previously thought.



8. What about our positive detection of dark matter particles?

What about our positive detection of dark matter particles?

As mentioned above, the research from the Italian project DAMA, which reported the discovery of dark matter, is very controversial.

To find the mysterious and elusive dark matter particles, researchers around the world have created underground detectors to try to observe WIMP particles interacting with ordinary matter.

To date, DAMA is the only project that has successfully demonstrated the existence of dark matter particles.

Other leading detection projects located in different parts of the world have reported conflicting results. The accuracy of the DAMA results has been hotly debated.



9. Can ordinary particles decay into dark matter?

Can ordinary particles decay into dark matter?

What if ordinary particles turned into dark matter particles? After all, we are already seeing something similar happen in electrons and neutrons. A solitary neutron slowly decays into a proton while an electron decays into a neutron.

Some researchers believe that 1% of these particles actually decay into dark particles. Bartosz Fornal and Benjamín Grinstein of the University of California at San Diego propose a solution to this gap which supposes that the neutrons decay 1% of the time into dark matter particles.

Since beam experiments would not detect these decays, their presumed neutron lifetime would be longer than the actual value.

Do you think that we will finally understand dark matter in the future?