Bulletin of Taras Shevchenko National University of Kyiv. Astronomy, no. 69, p. 30-37 (2024)
RELATIVISTIC SPHERICALLY SYMMETRIC ASTROPHYSICAL OBJECTS WITH SCALAR FIELDS
Valery ZHDANOV, DSc (Phys. & Math.), Prof.
Taras Shevchenko National University of Kyiv, Kyiv, Ukraine
Abstract
The interest in “exotic” models of astrophysical compact objects is due to breakthrough observational possibilities that have appeared in the last few years. At present, there are already dozens of gravitational wave detection events from the black holes mergers. The prospects of a long-wave gravitational detector in space are also inspiring. The study of “shadows” of supermassive black holes using the global interferometric system “event horizon telescope” is of considerable interest. Traditional X-ray studies of accretion disks around black holes also provide valuable information. New observational possibilities stimulate theoretical works that analyze the possibilities of applying “exotic” models to describe relativistic stars and black holes. According to outstanding theorists C. Mizner, K. Thorne and J. Wheeler, the relevance of such works is also related to the fact that “there must be something to compare Einstein’s theory with and show its advantages in a more contrasting way.” However, the general theory of relativity (GRT) has its internal problems and limits of application, and this stimulates studies of the gravitational-relativistic effects in the framework of alternative theories of gravity. Note that there are observational facts (problems of flatness, horizon, etc.) that have no explanation within the framework of the Standard Cosmological Model based on the GRT. They find a solution in the assumption of an inflationary expansion of the early universe, which requires either modifying the GRT or supplementing the Standard Model with additional types of interactions. In these additions, a typical element of consideration is a scalar field. The presence of a scalar field in a static system leads, as a rule, to the appearance of naked singularities (NS). The presence of NS is a challenge for GRT and its ability to predict the future. That is why R. Penrose proposed the well-known hypothesis of “cosmic censorship”, according to which NSs do not exist in the real universe. This hypothesis is quite popular, but its rigorous proof or disproof still does not exist. Instead, NSs (if they exist) could be ideal laboratories for testing fundamental interactions under extreme conditions, since in the vicinity of NSs the curvature invariants should reach Planck values. This review examines models of astrophysical configurations with non-linear minimally coupled scalar fields that can simulate ordinary black holes. The main attention is paid to static spherically symmetric systems with asymptotically flat space-time. A necessary element of such consideration are NSs arising in the case of common scalar-field potentials. The hypothesis of cosmic censorship, spherical singularities and problems of stability with respect to linear perturbations are discussed.
Key words
relativistic objects, black hole mimickers, naked singularities, modified gravity.
References
DOI: