by When you make a purchase through links on our article, Future and its syndicate partners may earn a commission.
Dark matter is notoriously antisocial, refusing to interact with light and “normal” matter, effectively making it invisible. But what scientists aren’t sure about is if dark matter interacts with itself.
If such particles are composed of dark matter do self-interaction through collision, and perhaps even mutual annihilation, new research suggests that galaxy clusters could be used as natural dark matter colliders. This method of detecting dark matter would depend on two of these large groups of galaxies coming together and smashing into each other.
Because these galaxy clusters are full of dark matter, astronomers could examine these cosmic crash sites for possible signs of dark matter interacting with itself.
Although it wouldn’t tell us exactly what particles make up dark matter, it would help eliminate dark matter models that don’t allow for self-interaction, bringing researchers closer to the true dark matter candidate.
“Galaxy clusters are also dominated by dark matter,” Jacqueline McCleary, assistant professor of physics at Northeastern University, said in a statement. “Eighty to 90% of its mass is dark matter, and the more massive the object, the faster the dark matter particles are moving. You’re basically studying very high-energy collisions.”
Related: Dark matter could play ‘matchmaker’ on supermassive black holes
Are dark matter particles anti-social ‘cosmic ghosts’?
The lack of interactions is one thing that makes dark matter so challenging to understand. Despite making up more than 80% of the universe of matter and providing the gravitational influence that prevents galaxies from flying apart, dark matter is effectively invisible because it does not interact with light. Similarly, dark matter particles slip through matter particles like cosmic ghosts.
These antisocial properties have led scientists to realize that dark matter cannot be made from atoms composed of electrons, protons, and neutrons. do they interact with light and each other. This sparked the search for a viable dark matter candidate particle.
“Everything in the universe is a particle and a wave and a field, so that’s the bottom line [assumption] dark matter must be a particle,” McCleary said. “The question is, what kind of particle, as ‘particle’ is very vague.”
The candidate particles range from “Weakly Interacting Massive Particles” or “WIMPS” to “MAssive Compact Halo Objects” or “MACHOs” (we see you, scientists), to tiny massless particles called axons or sterile neutrinos. Even small black holes left behind by the Big Bang, known as primordial black holes, have been candidates for dark matter.
The problem is, that all these skeptics have been discouraged by their detection and are therefore frustrated hypothetically.
The very similar nature of dark matter means that we cannot load dark matter particles directly into a particle accelerator on Earth, such as the Large Hadron Collider
(LHC), smash them together and determine their composition.
So while the LHC has broken some of the secrets of the “standard model of particle physics” by breaking apart protons and observing the resulting showers of particles, it seems dark matter, which lies outside that model, is excluded. table for the world’s most powerful particle accelerator.
The only way we can deduce the presence of dark matter is the only interaction it seems to be involved in. Dark matter has mass, so it makes space-time (a four-dimensional union of time and space), which it gives. gravitational influence.
That influence can tell everyday matter and light how to move, and we can sense that. It is through this indirect approach that we know that galaxies are surrounded by large halos of dark matter, and that there is also much dark matter near the hearts of galaxies.
Scientists also theorize that when galaxies are grouped together in giant clusters, this is the result of giant tendrils of invisible dark matter that spread through the Universe like the invisible web spun by a cosmic spider. This cosmic web also helps individual galaxies gather mass and grow, as its gravitational influence pulls in ordinary matter.
McCleary and colleagues previously recommended a man-made particle accelerator in favor of a natural accelerator. They reason that if clusters of galaxies and the dark matter they carry collide with enough force, observable dark matter interactions can occur—if indeed, dark matter interacts with itself.
These interactions could be as simple as dark matter particles colliding and bouncing off each other, or they could result in mutual annihilation and a burst of energy. When particles and antiparticles — say, an electron and its antiparticle, called a positron — collide, they annihilate each other, and their energy is released. Some models of dark matter suggest that it is its own antiparticle, meaning that one type of interaction could cause self-injury when two dark matter particles meet.
To test this idea, the team created simulations of galaxy cluster collisions on computers powerful enough to examine the collisions as far as particle-particle interactions. The simulation needed to be programmed with physical models of interactions between stars, gas and dark matter.
Using this simulation and others like it, scientists could build a roadmap for observing real dark matter collisions. From there, researchers could gather clues that help them determine some of the baseline characteristics a hypothetical dark matter particle would need. This could narrow down the dark matter of doubt.
“If you can measure some self-interaction, or if you can put a certain upper limit, you’re ruling in the classes of particles that may contain dark matter,” McCleary said. “If you measure some self-interaction, then you introduce another class of particles. You allow another class of theories.
“What this paper is also saying is that if you study a set of, say, 100 merging galaxy clusters, you have a chance of measuring the self-interaction of dark matter to some threshold.”
RELATED STORIES:
— What is dark matter?
— Dark matter ghosts its way through a powerful (and messy) collision of galaxy clusters
— Dark matter was detected hanging from the cosmic web for the 1st time
“It seems counterintuitive at first because we always want a positive answer: What?” McCleary concluded. “But in this case, we are kind of forced to say, What is it not? It is a process of elimination.”
The team’s research was published in April in the journal Monthly Notices of the Royal Astronomical Society.
