Focus on the Extremes: Harnessing the Power of Hard X-ray Focusing Optics to Probe Events Ranging from Solar Microflares to Stellar Superflares

Sensitive measurements of solar and stellar flares in the hard X-ray regime are necessary for investigating energy release and transfer during flaring events, as hard X-rays provide insight into the acceleration of electrons and emission from hot plasmas. This research harnesses the powerful capabilities of two instruments that use focusing optics for hard X-rays, the Focusing Optics X-ray Solar Imager (FOXSI), flown on three sounding rocket campaigns, and the Nuclear Spectroscopic Telescope Array (NuSTAR). With the heightened sensitivity of these instruments, it is finally possible to probe faint events in hard X-rays that have previously been elusive, ranging from small-scale solar events to bright X-ray flares on distant stars. In this presentation, we explore the nature of energy release for flaring events of vastly different magnitudes, including solar microflares observed by FOXSI-2 and superflares on young stellar objects (YSOs) observed by NuSTAR, and ask whether these events are linked by the common thread of the standard flare model. Additionally, we investigate the complexity of these solar microflares and the impact of ionizing radiation from YSO flares on protoplanetary disks. In exploring these uncharted regimes, this work probes some of the most intriguing mysteries of the stars, from coronal heating to the formation of planetary systems.