Sagittarius A*: A Supermassive Black Hole or a Spatially Extended Object?

Abstract

We report here on a calculation of possible orbits of the fast moving infrared source S1 which has been recently observed by near the Galactic center. It is shown that tracking of the orbit of S1 or any other fast moving star near Sgr A * offers a possibility of distinguishing between the supermassive black hole and extended object scenarios of Sgr A * . In our calculations we assumed that the extended object at the Galactic center is a non-baryonic ball made of degenerate, self-gravitating heavy neutrino matter, as it has been recently proposed by Tsiklauri & Viollier (1998a,b).Subject headings: black hole physics -celestial mechanics, stellar dynamics -dark matterelementary particles -Galaxy: center In spite of the vast and tantalizing work undertaken to resolve the issue of the existence of supermassive black holes (BH) at the centers of galaxies, it seems fair to say that, in this case, the jury is still out (for a current status see e.g. a review paper by Ho 1998). The discovery of quasars in the early 1960's provoked the idea that these extremely powerful emission sources draw their energy from accretion of matter onto compact, supermassive objects of 10 6 to 10 9 solar masses. This has led many to believe that these objects

Influence of the hydrodynamic drag from an accretion torus on extreme mass-ratio inspirals

“…(33) and (37) (52) for the definition of this quantity]. 6 Although this prescription is not exact, the results of Ref. [24] suggest that the relevant length scale in the Coulomb logarithm appearing in the second and third lines of Eq.…”

“…[4] for a detailed review), considerable effort has gone into trying to include the effects of a deviation from the Kerr geometry. These attempts are motivated by the fact that possible ''exotic'' alternatives to SMBHs have been proposed (e.g., boson stars [5], fermion balls, [6] and gravastars [7]), although the presence of these objects would require to modify radically the mechanism with which galaxies are expected to form. On the other hand, non-pure-Kerr templates might allow one to really map the spacetimes of SMBHs and to test experimentally the Kerr solution.…”

On the formation of degenerate heavy neutrino stars

“…As the potential inside such a nonrelativistic fermion star is shallow, the spectrum of radiation emitted by accreting baryonic matter is cut off for frequencies larger than 10 13 Hz [3,5], as is actually observed in the spectrum of the enigmatic radio source Sgr A * at the galactic center [10]. A fermion star with radius R < ∼ 20 light-days and mass M ≃ 2.6 × 10 6 M ⊙ is also consistent [6] with the observed motion of stars within a projected distance of 6 to 30 light-days from Sgr A * [9].Of course, it is well-known that 15 keV lies squarely in the cosmologically forbidden mass range for stable active neutrinos ν [11]. The existence of such a massive active neutrino is also disfavoured by the Super-Kamiokande data [12].…”

Astrophysical implications of gravitational microlensing of gravitational waves

“…Such gravitational events provide information about the nature of the lensing object, allowing us, in principle, to discriminate between a massive black hole and, for example, a compact star cluster (Maoz 1998) or a neutrino star (Munyaneza et al 1998;Capozziello & Iovane 1999) at the galactic center.…”