The Secret Metronome of Solar and Stellar Flares

The physics of flares, ferocious explosions on the Sun and other magnetically active stars, remains an enigmatic question in plasma astrophysics. One of the intrinsic features of flares is quasi-periodic pulsations (QPP) which are observed as irregular repetitive variations in the flaring electromagnetic emission. Being not predicted by the standard flare model, QPP appear in the majority of solar flares and in far more energetic stellar flares, suggesting to use their internal timescales, such as oscillation periods and damping times, as a secret natural metronome for constraining the main physical processes governing the development of flares in time. Understanding the origin of QPP and their role in a flare model has been hindered by the lack of commonly accepted theoretical models and inherent difficulties with the detection of QPP in observations. In order to transformatively advance the ongoing international and UK efforts in space weather and exploitation of the solar-stellar analogy, the proposed research project offers a new, paradigm-changing look at the long-standing problem of solar and stellar flares through the prism of QPP. The central engine of flares, spontaneous or induced reconnection of the magnetic field, is often seen to occur in a quasi-periodic manner in numerical simulations and observations of flares. We shall study the mechanisms for repetitive reconnection, developing the models of magnetically interacting coronal plasma structures during the process of coalescence instability and identifying its manifestations in multi-wavelength observations of flares. The correlation between the power of flares, magnetic topology and other parameters of active regions, and signatures of the oscillatory coalescence, as well as its role in the flare onset, will be investigated. Observations of QPP signals in the decay phase of solar and stellar flares and their modelling in terms of slow-mode MHD oscillations shall be used for constraining the processes of coronal heating, flare energy deposition and dissipation. Apart from developing and validating new theoretical models, the project also aims at bridging the gap between the manifold of existing diverse models and measurements of QPP in solar and stellar flares. The distinct classes of QPP characterised by common observational properties and the underlying physical mechanisms will be identified. The expected results will change transformatively our understanding of impulsive energy releases in astrophysical plasmas such as solar and stellar flares, as no contemporary time-dependent model of which is acceptable unless it adequately accounts for the phenomenon of QPP.