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تسجيل مستخدم جديدScalar field effects on the orbit of S2 star
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Precise measurements of the S-stars orbiting SgrA* have set strong constraints on the nature of the compact object at the centre of the Milky Way. The presence of a black hole in that region is well established, but its neighboring environment is still an open debate. In that respect, the existence of dark matter in that central region may be detectable due to its strong signatures on the orbits of stars: the main effect is a Newtonian precession which will affect the overall pericentre shift of S2, the latter being a target measurement of the GRAVITY instrument. The exact nature of this dark matter (e.g., stellar dark remnants or diffuse dark matter) is unknown. This article assumes it to be an scalar field of toroidal distribution, associated with ultra-light dark matter particles, surrounding the Kerr black hole. Such a field is a form of hair expected in the context of superradiance, a mechanism that extracts rotational energy from the black hole. Orbital signatures for the S2 star are computed and shown to be detectable by GRAVITY. The scalar field can be constrained because the variation of orbital elements depends both on the relative mass of the scalar field to the black hole and on the field mass coupling parameter.
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The highly elliptical, 16-year-period orbit of the star S2 around the massive black hole candidate Sgr A* is a sensitive probe of the gravitational field in the Galactic centre. Near pericentre at 120 AU, ~1400 Schwarzschild radii, the star has an or
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Two recent papers (Ghez et al. 2008, Gillessen et al. 2009) have estimated the mass of and the distance to the massive black hole in the center of the Milky Way using stellar orbits. The two astrometric data sets are independent and yielded consisten
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The star S2 orbiting the compact radio source Sgr A* is a precision probe of the gravitational field around the closest massive black hole (candidate). Over the last 2.7 decades we have monitored the stars radial velocity and motion on the sky, mainl
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[Abridged] The S-stars motion around the Galactic center (Sgr A*) implies the existence of a compact source with a mass of about $4times 10^6 M_odot$, traditionally assumed to be a massive black hole (BH). Important for any model is the explanation o
f the multiyear, accurate astrometric data of S2 and the challenging G2: its post-pericenter velocity decelerates faster than expected from a Keplerian orbit around the putative BH. This has been reconciled in the literature by acting on G2 a drag force by an accretion flow. Alternatively, we show that the S2 and G2 motion is explained by the core-halo fermionic dark matter (DM) profile of the fully-relativistic Ruffini-Arguelles-Rueda (RAR) model. It has been already shown that for 48-345 keV fermions, it accurately fits the rotation curves of the Milky-Way halo. We here show that, for a fermion mass of 56 keV, it explains the time-dependent data of the position (orbit) and light-of-sight radial velocity (redshift function $z$) of S2 and G2, the latter without a drag force. We find the RAR model fits better the data: the mean of reduced chi-squares of the orbit and $z$ data are, for S2, $langlebar{chi}^2rangle_{rm S2, RAR}approx 3.1$ and $langlebar{chi}^2rangle_{rm S2, BH}approx 3.3$ while, for G2, $langlebar{chi}^2rangle_{rm G2, RAR}approx 20$ and $langlebar{chi}^2rangle_{rm G2, BH}approx 41$. For S2 the fits of the $z$ data are comparable, $bar{chi}^2_{z,rm RAR}approx 1.28$ and $bar{chi}^2_{z,rm BH}approx 1.04$, for G2 only the RAR model fits, $bar{chi}^2_{z,rm RAR}approx 1.0$ and $bar{chi}^2_{z,rm BH}approx 26$. In addition, the critical mass for the gravitational collapse of a degenerate 56 keV-fermion DM core into a BH is $sim 10^8 M_odot$, which may be the initial seed for the formation of the observed central supermassive BH in active galaxies, such as M87.
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