Development of superconducting microcalorimeters for the HUBS mission

Hot Universe Baryon Surveyor (HUBS) is a proposed space-borne observatory for X-ray astronomy. The primary scientific objectives of the mission are to fill a void in probing the ecosystem of galaxies and thus to advance our understanding of galaxy formation and evolution, which is of fundamental importance in cosmology. More specifically, HUBS aims at directly detecting soft X-ray emission from diffuse gas of temperature exceeding 106 K, which is theoretically postulated to permeate the large structures in the cosmic web and also fill the extended halo of galaxies. However, although some indirect evidence exists, the presence of such hot gas has yet to be well established observationally, due to the lack of effective tools to probe it. In this paper, we describe the design of HUBS, focusing on its scientific payload, which employs superconducting technologies in the detector system, and particularly on progress in the development of superconducting microcalorimeters.