Looking for Axion Dark Matter Particles Near Neutron Stars With Radio Telescopes

Dark Matter Artist's Concept

An international research team is employing radio telescopes to search for axion dark matter particles near neutron stars.

In the 1970s, physicists uncovered a problem with the Standard Model of particle physics—the theory that describes three of the four fundamental forces of nature (electromagnetic, weak, and strong interactions; the fourth is gravity). They found that, while the theory predicts that a symmetry between particles and forces in our Universe and a mirror version should be broken, the experiments say otherwise. This mismatch between theory and observations is dubbed “the Strong CP problem”—CP stands for Charge+Parity. What is the CP problem, and why has it puzzled scientists for almost half a century?

In the Standard Model, electromagnetism is symmetric under C (charge conjugation), which replaces particles with antiparticles; P (parity), which replaces all the particles with their mirror image counterparts; and, T (time reversal), which replaces interactions going forwards in time with ones going backwards in time, as well as combinations of the symmetry operations CP, CT, PT, and CPT. This means that experiments sensible to the electromagnetic interaction should not be able to distinguish the original systems from the ones that have been transformed by either of the aforementioned symmetry operations.

In the case of the electromagnetic interaction, the theory matches the observations very well. As anticipated, the problem lays in one of the two nuclear forces—“the strong interaction.” As it turns out, the theory allows violations of the combined symmetry operation CP (reflecting particles in a mirror and then changing particle for antiparticle) for both the weak and strong interaction. However, CP violations have so far been only observed for the weak interaction.

Green Bank Telescope

Green Bank Telescope in West Virginia, USA. Credit: GBO / AUI / NSF

More specifically, for the weak interactions, CP violation occurs at approximately the 1-in-1,000 level, and many scientists expected a similar level of violations for the strong interactions. Yet experimentalists have looked for CP violation extensively but to no avail. If it does occur in the strong interaction, it’s suppressed by more than a factor of one billion (10?).

In 1977, theoretical physicists Roberto Peccei and Helen Quinn proposed a possible solution: they hypothesized a new symmetry that suppresses CP-violating terms in the strong interaction, thus making the theory match the observations. Shortly after, Steven Weinberg and Frank Wilczek—both of whom went on to win the Nobel Prize in physics in 1979 and 2004, respectively—realized that this mechanism creates an entirely new particle. Wilczek ultimately dubbed this new particle the “axion,” after a popular dish detergent with the same name, for its ability to “clean up” the strong CP problem.

CP Symmetry Operation Meson Particle

Illustration of the CP symmetry operation performed upon a meson particle. We say that the CP symmetry is violated if we observe that the original system (first frame) decays into a different particle than the CP transformed system (fourth frame). Credit: Kavli IPMU

The axion should be an extremely light particle, be extraordinarily abundant in number, and have no charge. Due to these characteristics, axions are excellent dark matter candidates. Dark matter makes up about 85 percent of the mass content of the Universe, but its fundamental nature remains one of the biggest mysteries of modern science. Finding that dark matter is made of axions would be one of the greatest discoveries of modern science.

In 1983, theoretical physicist Pierre Sikivie discovered that axions have another remarkable property: In the presence of an electromagnetic field, they should sometimes spontaneously convert to easily detectable photons. What was once thought to be completely undetectable, turned out to be potentially detectable as long as there is high enough concentration of axions and strong magnetic fields.

Green Bank Telescope West Virginia

Green Bank Telescope in West Virginia, USA. Credit: GBO / AUI / NSF

Some of the Universe’s strongest magnetic fields surround neutron stars. Since these objects are also very massive, they could also attract copious numbers of axion dark matter particles. So physicists have proposed searching for axion signals in the surrounding regions of neutron stars. Now, an international research team, including the Kavli Institute for the Physics and Mathematics of the Universe (Kavli IPMU) postdoc Oscar Macias, has done exactly that with two radio telescopes—the Robert C. Byrd Green Bank Telescope in the US, and the Effelsberg 100-m Radio Telescope in Germany.

The targets of this search were two nearby neutron stars known to have strong magnetic fields, as well as the Milky Way’s center, which is estimated to host half a billion neutron stars. The team sampled radio frequencies in the 1-GHz range, corresponding to axion masses of 5–11 micro electron-volt. Since no signal was seen, the team was able to impose the strongest limits to date on axion dark matter particles of a few micro electron-volt mass.

Reference: “Green Bank and Effelsberg Radio Telescope Searches for Axion Dark Matter Conversion in Neutron Star Magnetospheres” by Joshua W. Foster, Yonatan Kahn, Oscar Macias, Zhiquan Sun, Ralph P. Eatough, Vladislav I. Kondratiev, Wendy M. Peters, Christoph Weniger and Benjamin R. Safdi, 20 October 2020, Physical Review Letters.
DOI: 10.1103/PhysRevLett.125.171301

10 Comments on "Looking for Axion Dark Matter Particles Near Neutron Stars With Radio Telescopes"

  1. Dark matter doesn’t exist so we will look for something and if we find anything it will be called dark matter. But the very name means it doesn’t exist it was just a thought. Same as when u have a thought same thing so don’t stop thinking thoughts are great and their not dark.

  2. Dark energy is the wrong term it should just be E as in the vibrating universe. And the vibration may have started with the first blacksphere. And has increased how ever so slight with the creation of each blacksphere. And will continue to increase with time and creation. Or maybe that’s how the first blacksphere was created with a vibrating universe.

  3. After all (E Equals MC squared) that might be it after all. The answer? What do you think

  4. … collection of muddled views, that yield way too many exceptions…
    … it should be like: loosening the knot by knot, but it gets tight and more tight…

  5. So let’s talk about the cosmic constant. So you say the universe would collapse on itself if it wasn’t expanding correct. I don’t believe you from what I can tell the cosmic constant simply means moving. And when I say moving I mean it’s vibrating the universe is vibrating. That’s why there’s no collapse and it’s not expanding it’s vibrating. This is gonna sound crazy to all of you but here it goes. I was sleeping one afternoon and was awoken abruptly and when I sat up everything looked the same except out of the corner of my eye it was black and it was vibrating. When I looked it was gone but I looked str8 ahead again and it was back but only when I didn’t look. Sounds strange I know but it happened. It lasted for a minute or so and then It was gone all together but it was there and it was vibrating. It Freaked me out and ever since I knew it was vibrating. Sounds nuts but I’m telling you today it’s vibrating. I tried explaining it once before. So that’s what I believe the cosmic constant is vibration so fast it makes everything move nothing in the universe is still and that’s why.

  6. And that’s why the universe hums.

  7. So when someone says dark energy think about what I just told you. I have no reason to say what I just said but what I said is true. A vibrating universe is the answer. Have a great day.

  8. Very good article. Axion and dark matter and dark energy will be duscussed in the final chapter of my second book to be published by Feb or March.

  9. … yeah, it is just sure that scientist have done proper estimation, well the things are traveling through the space that that is elastic, and grows over time, and then there is time dilatation, and limit to the speed of the light, and lenses etc, well that is just so easy to take all into account and add it all up…

  10. Lee Berry, I also had the same experience as you during an altered state of sleep known as “sleep paralyses”. I woke up to find my body asleep and unable to move, the only part of my existence that seemed to be active was my conciousness. My initial instinct was to try and snap out of it and wake my body, however my curiosity took over and instead I decided to just relax and explore the state I had found myself in. But nothing could have prepared me for what was about to follow…It began with a feeling like I was vibrating rapidly, then the sound of that subtle background hum resembling tinnitus became louder and louder until it was almost deafening. As the vibrations intensified I suddenly fell off my bed, but instead of hitting the floor I passed right through it, I hovered underneath the floorboards where I observed all the ducted heating pipes and some plumbing. As I gradually floated back into my room I noticed that everything in my room although in the same position appeared to be constructed of tiny pixels that were vibrating and the sound I was hearing was the frequency of that vibration. The only way I could interpret it was that the quantum world is within a parallel dimension of its own. All the energy generated by the physical universe translates into an entire seperate dimension. Its as if we exist in both dimensions simultaneously except that our physical bodies are in the physical realm governed by the law of physics while our energy is in the other dimension governed by quantum physics. Both dimensions overlap in such a way that they function in sync. The one thing that can switch between the two dimensions is our conciousness however as long as our physical bodies are active our conciousness is only able to reside in this dimension, its only during events where we can maintain our conciousness while retiring our physical body that we become aware of the macro dimension. It sounds like you caught a glimpse just as your awareness was switching between the two.

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