A central question in the ongoing search for dark matter: What is it made of? One possible answer is that dark matter consists of particles known as axions. A team of astrophysicists led by researchers from the Universities of Amsterdam and Princeton has shown that if dark matter consists of axions, it can appear as a faint extra glow emitted by pulsating stars. His work was published in the journal Physical Examination Letters.

Dark matter may be the most sought-after component of our universe. Surprisingly, this mysterious form of matter, which physicists and astronomers have so far failed to detect, is believed to make up a large portion of what exists.

At least 85% of the matter in the universe is believed to be “dark” and this is now only visible due to the gravitational pull it exerts on other astronomical objects. It is clear that scientists want more. They want to actually see dark matter, or at least detect its existence directly, not just infer it through gravitational effects. And of course they want to know what happened.

Troubleshoot two problems

One thing is clear: Dark matter cannot be the same type of matter that you and I make. If this were the case, dark matter would behave like normal matter; it would form objects like stars, they would shine and there would be no “darkness” anymore. That’s why scientists are looking for something new; A type of particle that no one has yet discovered and that probably interacts very weakly with the types of particles we know explains why this component of our world has remained elusive until now.

There are many clues on where to look. A popular hypothesis is that dark matter may consist of axions. This hypothetical type of particle was first proposed in the 1970s to solve a problem that had nothing to do with dark matter. It turns out that the distinction between positive and negative charges inside the neutron, one of the building blocks of ordinary atoms, is surprisingly small. Of course, scientists wanted to know why.

It turns out that the presence of yet undiscovered types of particles that interact very weakly with the components of the neutron can cause just such an effect. Later, Nobel laureate Frank Wilczek came up with a name for the new particle: axis – which not only resembled other particle names such as proton, neutron, electron and photon, but was also inspired by the laundry detergent of the same name. Axion was there to solve the problem.

He can actually clear two of them, although they are never detected. Various theories of fundamental particles, including string theory, one of the leading candidate theories for unifying all forces in nature, appeared to predict that axion-like particles might exist. If the axions were really there, could they explain some, or even all, of the missing dark matter? Perhaps, but an additional question plaguing all dark matter studies was equally relevant to the axions: If so, how can we see them? How to make something “dark” visible?

Illuminating dark matter

Fortunately for the axes, there seems to be a way out of this impasse. If theories predicting axons are correct, they would be expected to be mass-produced throughout the universe, and some axons could also turn into light in the presence of strong electromagnetic fields. We can see when there is light. Could this be the key to detecting axions and therefore detecting dark matter?

To answer this question, scientists first had to ask themselves where the strongest known electric and magnetic fields in the universe originated. The answer is: in the regions around rotating neutron stars, also known as pulsars. These pulsars, short for “pulsating stars,” are dense objects with about the same mass as our Sun, but their radii are about 100,000 times smaller and they are only about 10 km away. Because pulsars are so small, they spin at tremendous frequency and emit bright, narrow beams of radio radiation along their spin axes. The pulsar’s rays can reach Earth like a beacon, making it easier to observe the pulsating star.

But the pulsar’s massive spin does more. It turns the neutron star into an extremely powerful electromagnet. This could mean that pulsars are very efficient axis factories. An average pulsar can produce a 50-digit number of axions every second. Some of these axions can be converted into observed light due to the strong electromagnetic field around the pulsar. That is: if axes exist, but this mechanism can now be used to answer this very question. Just look at pulsars, see if they emit extra light, and if so, determine if that extra light is coming from the axions.

Imitation of fine glitter

Of course, as always in science, making such an observation is not that easy. The light emitted by the axons, detectable as radio waves, would be only a small fraction of the total light sent to us by these bright cosmic beacons. To see the difference, let alone measure this difference and convert it into a measurement of the amount of dark light, one would need to know very precisely what a pulsar without axes would look like and what a pulsar with axes would look like. case.

This is exactly what a team of physicists and astronomers did. Through the joint efforts of the Netherlands, Portugal, and the United States, the team has created a comprehensive theoretical framework that allows for a detailed understanding of how axons are formed, how axons escape the gravity of a neutron star, and how they form during their lifetime. If they escape, they turn into low-energy radio radiation.

The theoretical results were then fed into a computer to simulate the formation of axions around pulsars using modern numerical plasma simulations developed to understand the physics of how pulsars emit radio waves. Following the virtual creation, the propagation of the axes through the electromagnetic fields of the neutron star was simulated. This allowed the researchers to quantitatively understand the subsequent production of radio waves and model how this process would provide an additional radio signal on top of the internal radiation produced by the pulsar itself.

Testing action models

The theory and simulation results were then subjected to initial observation testing. Using observations of 27 nearby pulsars, the researchers compared observed radio waves with models to see whether any measured excesses could provide evidence for the existence of axions. Unfortunately, the answer was no, or more optimistically, not yet. The Axions don’t jump on us right away, but perhaps this shouldn’t have been expected. If dark matter could reveal its secrets so easily, it would be observed long ago.

Therefore, hope of detecting axions with smoke weapons now rests on future observations. By the way, the fact that radio signals from the axes are not currently observed is an interesting result in itself. The first comparison between simulations and real pulsars identified the strongest limits to date on the interaction of the axions with light.

Of course, the ultimate goal is to do more than set constraints: either to show that axions exist, or to make sure that axions are a component of dark matter. The new findings are a first step in this direction; these are just the beginning of an entirely new and highly interdisciplinary field that has the potential to significantly advance axial research. Source