Exploring active galactic nuclei by polarisation of radiation in infrared/optical/ultraviolet/X-ray spectral domains
The center of the Milky Way harbours a super-massive compact dark body that influences motion of stars and gas in its neighborhood. Evidence points to a 106 solar-mass black hole, or one of even more exotic alternatives. Parameters of the black hole and the nuclear star cluster have been measured by methods of photometry and spectroscopy in near-infrared, X-ray and millimeter radio regimes. Modern techniques have been employed: interferometry and high-resolution imaging with adaptive optics (on the contrary, visible light is not suitable to study Galactic center because of high extinction along our line of sight). Nevertheless, the mentioned methods provide very important but limited information about three-dimensional distribution of gas around the Galactic center. Our current knowledge is restricted to the projected images and radial velocities of matter. Working towards future technique of X-ray polarimetry, the authors of the present paper propose a new approach that will allow to gather missing pieces information. The main observational results will become available with one of the proposed X-ray Imaging Polarimetry missions where the Czech team participates in preparations for the science consortium. In the recently published paper, for the first time, technical details are calculated to show how a feasible mission can provide us with detailed knowledge about the past history and present structure of the Galactic center. One of exciting topics that the authors address is whether the currently inactive Milky Way behaved like an active galaxy in the recent past.