In this study, new concepts were used: gravitational strings and gravitational cells. This made it possible to obtain the following scientific results: The quantum formula of the graviton was obtained. Based on this formula, the mass of an electron inside a black hole was determined, based on three fundamental physical constants h, q, c. Theoretically, the reaction of the formation of a hydrogen atom from the substance of a black hole was modeled. The mass of the hydrogen atom obtained through calculations coincided with the experimental mass of the hydrogen atom. The relative discrepancy between the calculated and experimental masses was only 5 ∙〖10〗^(-7) and is completely related to the mass defect as a result of neutrino emission, which is confirmed by the calculations presented in the study. The quantum formula of the gravitational string was obtained. This formula has been applied to the results of a well-known experiment to study the Casimir effect. The new formula made it possible to determine the minimum distance of action of gravitational forces (746 nm), which coincided with the beginning of the action of the Casimir force. The distance between the plates (30 nm) was also determined, at the boundary of which the exchange of photons between atoms transforms into the exchange of electrons. In this study, an upper limit on the mass of the graviton was determined. The result obtained is confirmed by the results of astrophysical observations presented in this article. A formula for the gravitational constant was obtained, and other results of scientific importance were presented.