We show the scientific potential of a Soft X-ray Imager (SXI) onboard the ESA-CAS satellite SMILE for investigating cosmic X-ray sources of various types. We show that this instrument, albeit designed for X-ray imaging of the interaction of solar wind with the magnetosheath of the Earth, is also essential for astrophysics because it is able to provide wide-field imaging of the sky in the soft X-ray region. Regarding sufficiently luminous X-ray sources with continuous spectra to be observable by the X-ray monitor MAXI/ISS to assess the object types and their light curves that are expected to be detected by SXI/SMILE, the compact sources accreting matter are promising targets for evaluating the possibilities of SXI. We assumed only the cosmic objects located in the planned fields to be observed by SXI.

The North Polar Spur is the largest and most conspicuous emission structure in both the radio and X-ray domain. Since its discovery about 60 years ago, its origin has been debated: is it either an ancient remnant of a nearby supernova explosion, or part of a 'hypershell' originating from the Galactic central region. The debate gained new momentum after the discovery of the so-called Fermi Bubbles at gamma energies more than 10 years ago. However the main argument against the hypershell theory was the lack of a southern counterpart symmetric to the northern structure. The main task of the X-ray telescope eROSITA on the Russian/German SRG mission is to systematically survey the sky eight times. Already in the first survey the existence of the southern counterpart could be proven. Henceforth, this structure was named eRSOSITA Bubbles in reference to the Fermi Bubbles. Since then, several questions are being debated: What is the origin of the eROSITA Bubbles, an AGN activity about 15 million years ago, or a quasi-continuous starburst activity? What is the connection to the galactic halo? Do we observe a similar scenario in other nearby spiral galaxies?