Dark Matter

Deja Vu? Dark Matter: Will It Collide Or Won’t It Collide? That Is The Question

Dark matter is a mystery in itself. In fact, scientists don’t really know what dark matter is. However, a new theory published in Physical Review Letters suggests that dark matter may be very similar to pions, the particles responsible for binding atomic nuclei together.

Pions have been well-known to science since the 1930s, and, with this new theory, a sort of déjà-vu idea, seeing dark matter as pions, researchers may actually be able to study the behavior of dark matter, according to Phys.org.

But, pions aside, another question begs to be asked. If scientists themselves cannot define dark matter, why is it important to theorize on the existence of it?

Let’s start with a case of gas.

NASA explained it best. Stars make up galaxies. Galaxies sometimes form clusters, and, in some clusters, the spaces between galaxies are made up of gas. Very hot gas.

The heat of this gas can be so intense gas that astronomers are not able to look through visible light telescopes and actually see it. The gas is only visible as gamma or X-rays. After measuring the gas and determining how much there was between galaxies in clusters, researchers discovered that an astonishing five times more material must be within the clusters than instruments can detect. Thus, the term “dark matter” came about.

It is widely accepted that most of the matter making up the known universe, 80 percent of all matter in existence, per the Inquisitr, is comprised of dark matter (DM).

Dark, because this matter has no color, no electrical charge, it does not self-interact much at all, and it is cold, per Phys.org.

There are a few theories.

Dark matter could be a thermal relic.

One theory suggests that dark matter is a “thermal relic” from the early universe. This idea holds that all particles are in thermal equilibrium until expansion and cooling occurs. At that point, particle interaction rates slow, causing them to freeze-out. Unstable particles then vanish, and stable particles that remain reach what’s known as their thermal relic density.

The theory of thermal relics has two opposing viewpoints: SIMPs vs. WIMPs.

On one hand, some scientists believe the most likely candidates for dark matter are weakly interacting massive particles (WIMPs), though no particle known today matches WIMP properties.

In December, 2014, researchers at University of California, Berkeley, Tel Aviv University, Israel, and Stanford University presented a new thermal relic theoretical model. They suggested that it is not WIMPs, but strongly interacting massive particles (SIMPs) that are true dark matter particle candidates.

These particles? Do they collide or do they not collide? That is the question behind the new theory.

Conventional theories have it that dark matter particles would not collide. Instead, they would “slip past” one another.

The new theory, published in Physical Review Letters on July 10, predicts dark matter is not only likely to collide, but it is likely to interact with itself within galaxies or clusters of galaxies, which can explain the extra mass distributions calculated in clusters.

“[The new theory] can resolve outstanding discrepancies between data and computer simulations,” suggested Eric Kuflik, a postdoctoral researcher at Cornell University.

University of California, Berkeley, postdoctoral researcher Yonit Hochberg added, “The key differences in these properties between this new class of dark matter theories and previous ideas have profound implications on how dark matter can be discovered in upcoming experimental searches.”

Experiments on the dark matter can now be conducted through use of the Large Hadron Collider, the new SuperKEK-B, and a proposed experiment, SHiP.

Conventional theories predict that dark matter particles would not collide, rather they would slip past one another. Hochberg et al. predicts dark matter SIMPs would collide and interact with one another. [Credit: Kavli IPMU]
Conventional theories predict that dark matter particles would not collide, rather they would slip past one another. Hochberg, et al., predicts dark matter SIMPs would collide and interact with one another. [Credit: Kavli IPMU]
Now, what about those pions and déjà-vu?

A pion is a type of hadron (as in that famous Large Hadron Collider) and is defined as a “group of three unstable elementary particles,” per The Free Dictionary. Two of the particles are charged, and one is neutral.

Hitoshi Murayama is a professor of physics at the University of California, Berkeley, and director of the Kavli Institute for the Physics and Mathematics of the Universe at the University of Tokyo.

“We have seen this kind of particle before. It has the same properties,” said Murayama, “same type of mass, the same type of interactions, in the same type of theory of strong interactions that gave forth the ordinary pions. It is incredibly exciting that we may finally understand why we came to exist.”

Shedding some light on dark matter may not be a matter of déjà-vu for most people, but the implications of better understanding gravitational forces in the universe are heavy enough for anyone clever enough to look to the stars for answers.

[Image via Chandra / Getty Images]