A particular kind of dark matter can explain multiple mysterious signals coming from the centre of our galaxy.
Proposed by scientists at King's College London, the research makes use of data coming from telescopes deep in the Milky Way.
Despite making up most of the matter in the Universe, dark matter has never been directly detected and its fundamental nature remains unknown. Instead, astronomers look for evidence of dark matter through indirect signs of how it might behave in space, including unexplained signals observed near the centre of our galaxy - the Milky Way.
Research has previously linked what's termed 'excited dark matter' to one of these signals - an observed sharp spike in gamma rays at a specific energy known as the 511-keV emission line. However, this is the first time the excited dark matter model was shown to explain up to three unexplained signals coming from the centre of our galaxy simultaneously.
When we look at well-known astrophysical events, like star explosions, they haven't been able to provide a full explanation for mysteries like the specific energy and shape we've observed coming from the centre of the Milky Way. Now, we've shown how one excited dark matter model could account for at least two - possibly even three - of these kind of unexplained signals at once.
Dr Shyam Balaji, Postdoctoral Research Fellow in the Department of Physics.
Excited dark matter is proposed to occur when particles of dark matter bump into each other and briefly store extra energy in an "excited" state before releasing it. When the energy is released, it's theorised it produces positively-charged electrons called positrons, and these positrons can be seen indirectly in space using special space-based telescopes like the INTEGRAL experiment.
By using these observations, scientists at King's modelled how positrons travel through the Milky Way. They proposed that a single excited dark matter scenario could simultaneously explain not only the 511 keV signal but also a very high-energy light coming from the centre of our galaxy, known as the 2 MeV gamma-ray continuum.
The team say the model could potentially explain a third mysterious signal - an unusually high ionisation in gas in a region near the Galactic centre known as the Central Molecular Zone (CMZ). Known sources such as cosmic rays, high energy particles ejected by complex processes in the inner Galaxy, have failed to provide an adequate explanation for the ionisation process and the new model demonstrates that the same positrons injected by dark matter could contribute significantly.
The team say future space missions designed to detect low-energy gamma rays could directly test their predictions. If confirmed, the results would provide important new evidence about how dark matter behaves.
If one mechanism could account for several long-standing unexplained observations in space, it gives a much clearer direction for future research. Within the next generation of space missions, we may finally be able to test the theory of whether dark matter is behind some of the Milky Way's most persistent mysteries and learn more about the mysterious substance itself in the process.
Damon Cleaver, PhD Candidate in the Theoretical Particle Physics and Cosmology Group.
