The Hunt for Axion Dark Matter, by Professor Ed Daw
27th Annual General Meeting of the Flamsteed Astronomy Society
Our chair Bobby Manoo opened the 2026/27 Flamsteed season with our formal AGM reflecting on the last 12 months. Bobby drew members’ attention to the AGM video statement which was previously circulated and outlined some of the key accomplishments, with talks, workshops, trips and liaison and involving significant outreach and engagement with approximately 8,000 members of the public and contribution of 1,100 volunteer hours. Bobby outlined the exciting year ahead and plans for member events which can be found on the FAS website. Thanks were made to all FAS Committee members both retiring, continuing and newly joining.
Bobby himself announced his departure as Chair reflecting on the changes he has been able to implement during his stewardship – refreshing observing activities, improved communication (website, weekly newsletters) and committee structure, resumption of society trips, strengthening of outreach and renewal of relationships with other observing societies and the RMG. Paul May was elected to the Chair role and his first act was to lead members and the committee in recognising and thanking Bobby for his exceptional five years of leadership. We presented Bobby with an honorary membership of FAS, a framed print from the RMG and some cake!
Presentations to Bobby, and cutting the cake! Pictures by Mike Meynell, Paul May and Amy Scammell
Paul outlined his desire to build on Bobby’s work and maintain the Society’s strengths, continuing to develop the partnership with RMG, considering an annual astronomy fair, involving younger members and extending merchandise to members. The FAS Committee is here to serve our members and to do this effectively we need to know what people want. Paul outlined that a survey will be being circulated shortly – please respond!
Axion Dark Matter
We began our 2026/27 season with a fantastic main lecture from Professor Ed Daw, Professor of Physics at the University of Sheffield.
Dark matter is a form of matter that does not give off, reflect or absorb light, which means we cannot see it directly with telescopes. For that reason, it might more accurately be described as “invisible matter”. It is called “matter” because it has mass and exerts gravity, but it appears to interact very weakly, if at all, with ordinary matter through the electromagnetic force. In simple terms, we know it is there not because we can see it, but because we can measure its gravitational effects.
The strongest early evidence came from the way galaxies and galaxy clusters move. In the 1930s, Fritz Zwicky studied the motion of galaxies within the Coma Cluster and found that they were moving too fast to be held together by the visible matter alone. Later, Vera Rubin’s work showed that stars in the outer parts of spiral galaxies were orbiting much faster than expected. If galaxies only contained the stars, gas and dust we can see, those outer stars should move more slowly; instead, their motion suggests that galaxies sit inside much larger halos of unseen mass.
Further evidence comes from gravitational lensing, where massive objects bend the light from more distant galaxies behind them. The amount of bending often shows that there is far more mass present than can be accounted for by visible matter. Measurements of the cosmic microwave background (CMB) - the afterglow of the early Universe - also point to a Universe in which ordinary matter makes up only a small fraction of the total matter content.
Taken together as Ed remarked these observations either suggest that we are not very good at physics or that there is something else out there – that most of the matter in the Universe is not made of familiar atoms.
Exactly what dark matter is remains one of the major unsolved questions in physics. Ed outlined that there are a number of theories that have been considered:
Rocks: Rocks are baryonic matter – atoms made mostly of nuclei and electrons. If there were enormous amounts of unseen asteroids, planets or other cold matter floating through space their gravity could contribute to this missing mass. There are challenges with this idea – there are cosmological constraints on how much ordinary matter exists, rocks would be revealed through gravitational lensing and rocks also interact with light and gas.
Neutrinos: Neutrinos have a tiny amount of mass, no electric charge, interact extremely weakly with ordinary matter, don’t emit light and travel through matter almost unhindered. Billions of neutrinos pass through the earth every second. The challenge is that neutrinos are extremely fast moving and hot and as such don’t gather together easily to form structures. Observations tell us that the universe formed lots of relatively small structures early on which requires a lot of slow moving or cold matter. A further possibility, not discussed in the lecture, is a hypothetical heavier type of neutrino called a sterile neutrino. They could be detected through their decay into an ordinary neutrino and a photon. To date they remain hypothetical.
Weakly Interacting Massive Particles (WIMPs): If they exist, WIMPs have mass and produce gravity, they neither emit nor absorb light significantly so we can’t see them directly, they only weakly interact with ordinary matter and they move slowly enough to clump into halos around galaxies. Much time (and money!) has been spent on the detection of WIMPs but to date none have been detected.
Ed outlined an alternative option – axions. Similarly to a WIMP an axion is a proposed and hypothetical particle. Frank Wilczek and Steven Weinberg independently predicted axions from the theory proposed by Roberto Peccei and Helen Quinn to solve the strong CP problem - the puzzle of why the strong nuclear force appears to preserve a symmetry combining mirror reflection with exchanging particles and antiparticles. Axions could also have the properties needed to form dark matter. Whilst axions have not yet been detected the possibility that they could solve two problems makes them an attractive candidate for dark matter.
Professor Ed Daw speaks to the Flamsteed. Pictures by Mike Meynell.
So how might we detect axions? Ed focused on haloscopes, but there are also other approaches:
Haloscopes (dark matter searches): Use powerful magnets and ultra-cold microwave cavities to search for photons produced by the conversion of axions.
Helioscopes (solar axions): Point strong magnets at the Sun and look for axions converting into X-rays.
Laser experiments: Try to generate axions from laser light in the laboratory and search for their conversion back into photons beyond a barrier.
Astrophysical observations: Look for indirect signatures of axions in stellar cooling, supernovae, neutron stars, and the behaviour of light from distant galaxies.
Detecting axions is challenging as they would interact extremely weakly with matter, so experiments must detect extraordinarily small signals amid background noise.
There are a number of experiments underway at present including:
ADMX (Seattle, USA): The Axion Dark Matter eXperiment (ADMX) at the University of Washington is one of the world’s leading axion haloscopes, using a powerful magnetic field and ultra-sensitive microwave cavity to search for dark matter axions passing through the Earth.
CAPP (Daejeon, South Korea): The Center for Axion and Precision Physics Research (CAPP) at KAIST operates a suite of state-of-the-art axion haloscope experiments, using high-field magnets, dilution refrigeration and quantum-limited detectors to probe some of the most promising axion parameter space.
Ed’s own group at Sheffield leads UK efforts to develop next-generation quantum sensors for hidden-sector particles, including axions, using ultra-low-temperature experiments and quantum-enabled detectors, while also contributing to the international ADMX collaboration. Ed outlined the ongoing efforts to develop and evolve instrumentation to aid the hunt for dark matter.
This was a hugely entertaining lecture – we really recommend you view it online – delivered with great enthusiasm by a brilliant speaker who, as one of his colleagues once joked, specialised in “searches for things that would never be found”. His involvement in detecting gravitational waves had rather spoiled that joke!
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