An estimate the rotation period of cometary nuclei is important for understanding and describing the physical processes of the cometary activity. Unfortunately, the measurements of the rotation periods of the comet nucleus depend on the model assumptions and it is one of the main reasons for the scatter of the estimates given in various articles for a given comet. More...

Ultraluminous X-ray sources (ULXs) are located in external galaxies, their X-ray luminosities are thousand times greater than those of brightest black holes in the Galaxy. It has been found in the VLT and BTA observations of extragalactic stellar clusters related to the ULXs, that these objects are stellar-mass black holes with supercritical accretion disks. More...

Recent studies indicate that stars are most likely forming within the binary and multiple systems. In our Galaxy, according to various estimates, at least 50 percent of stars have companions. Therefore, the study of binary and multiple stars is important for understanding the mechanisms of star formation in general. More...