Physics

Permanent URI for this community

https://testres.nu.edu.kz/handle/123456789/512

Browse

Browsing Physics by Subject "astrophysics"

Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Note on the effect of a massive accretion disk in the measurements of black hole spins
    (2014-06-25) Bambi, Cosimo; Malafarina, D.; Tsukamoto, Naoki
    The spin measurement of black holes has important implications in physics and astrophysics. Regardless of the specific technique to estimate the black hole spin, all the current approaches assume that the space-time geometry around the compact object is exactly described by the Kerr solution. This is clearly an approximation, because the Kerr metric is a stationary solution of the vacuum Einstein equations. In this paper, we estimate the effect of a massive accretion disk in the measurement of the black hole spin with a simple analytical model. For typical accretion disks, the mass of the disk is completely negligible, even for future more accurate measurements. However, for systems with very massive disks the effect may not be ignored.
  • No Thumbnail Available
    ItemRestricted
    Supernova distribution about the Galaxy Center
    (Nazarbayev University School of Science and Technology, 2017-04) Nussupbekov, Ayan
    The discovery of the gravitational waves opened various possibilities in astrophysics. One of them is to use the supermassive black holes at the Galaxy center as focusing lenses for gravitational waves. Because of it, it is essential to know the radial distribution of supernova about the Galaxy center. In this thesis work, we presented supernovas radial distribution through the distribution of supernova remnants. We analyzed existing catalogs of supernova remnants by plotting their histograms. We used Bayesian approach to find the best-fitting probability density function. We used the exponential model to determine the radial surface distribution of supernova remnants. Our the best fitting exponential model is in great correspondence with the distribution obtained by G.L.Case&D.Bhattacharya [5] and Kodaira [12]. Also, we discussed applied observational selection effects. Moreover, we examined uncertainties related to the distance estimates of supernova remnants.
  • Thumbnail Image
    ItemOpen Access
    The general solution for relativistic spherical shells
    (2005) Kijowski, J.; Magli, G.; Malafarina, D.
    The general exact solution of the Einstein-matter field equations describing spherically symmetric shells satisfying an equation of state in closed form is discussed under general assumptions of physical reasonableness. The solutions split into two classes: a class of “astrophysically interesting” solutions describing “ordinary” matter with positive density and pressure, and a class of “phantom-like” solutions with positive density but negative active gravitational mass, which can also be of interest in several “very strong fields” regimes. Known results on linear-barotropic equations of state are recovered as particular cases.