Full Three Dimensional Orbits For Multiple Stars on Close Approaches to the Central Supermassive Black Hole

Abstract

With the advent of adaptive optics on the W. M. Keck 10m telescope, two significant steps forward have been taken in building the case for a supermassive black hole at the center of the Milky Way and understanding the black hole's effect on its environment. Using adaptive optics and speckle imaging to study the motions of stars in the plane of sky with ±∼2 mas precision over the past 7 years, we have obtained the first simultaneous orbital solution for multiple stars. Among the included stars, three are newly identified (S0-16, S0-19, S0-20). The most dramatic orbit is that of the newly identified star S0-16, which passed a mere 60 AU from the central dark mass at a velocity of 9,000 km/s in 1999. The orbital analysis results in a new central dark mass estimate of 3.6(±0.4) × 10 6 (( Ro 8kpc ) 3 M . This dramatically strengthens the case for a black hole at the center of our Galaxy, by confining the dark matter to within a radius of 0.0003 pc or 1,000 R sh and thereby increasing the inferred dark mass density by four orders of magnitude compared to earlier estimates.With the introduction of an adaptive-optics-fed spectrometer, we have obtained the first detection of spectral absorption lines in one of the high-velocity stars, S0-2, one month after its closest approach to the Galaxy's central supermassive black hole. Both Br γ (2.1661 µm) and He I (2.1126 µm) are seen in absorption with equivalent widths and an inferred stellar rotational velocity that are consistent with that of an O8-B0 dwarf, which suggests that S0-2 is a massive (∼15 M ), young (<10 Myr) main sequence star. Similarly, the lack of CO detected in our first AO spectra suggest that several other of the high-velocity stars are also young. This presents a major challenge to star formation theories, given the strong tidal forces that prevail over all distances reached by these stars in their current orbits and the difficulty in migrating these stars inward during their lifetime from further out where tidal forces should no longer preclude star formation.

Massive stars in subparsec rings around galactic centres

“…We shall first consider the case of Sgr A* for which the mass of the SMBH is estimated to be M BH ≃ 3.5 × 10 6 M ⊙ (Schödel et al 2002; Ghez et al 2003). For this particular example, we shall accept that Σ * = 0.001 Σ and that the initial masses of protostars are M * = 0.1 M ⊙ .…”

Is There a Supermassive Black Hole at the Center of the Milky Way?

“…In 2002, Munyaneza & Viollier 71 showed that the then existing stellar motion data could only be fit by a restricted range of parameter space for a supermassive black hole, but could be easily fit by Fermion ball models. Subsequent observations of stellar orbits 38,39,40 showed that the supermassive black hole predictions were indeed met, and that the stars moved with speeds greater than allowed by their Fermion ball model. We note that the density limit employed in this section was the one obtained only from the orbits of stars.…”

Investigating the Relativistic Motion of the Stars Near the Supermassive Black Hole in the Galactic Center

“…While the first Keplerian orbital elements of the S2's orbit could be derived from the pre-periapse data, the situation improved significantly after the periapse passage of S2 in 2002. NIR adaptive optics (AO) imaging allowed the derivation of detailed Keplerian orbital elements (Schödel et al 2002;Ghez et al 2003). NIR spectroscopy resulted in radial velocities, and hence in a determination of the mass and the distance to the GC derived from the orbital data (R 0 ; Ghez et al 2003Ghez et al , 2005Eisenhauer et al 2003).…”

“…NIR adaptive optics (AO) imaging allowed the derivation of detailed Keplerian orbital elements (Schödel et al 2002;Ghez et al 2003). NIR spectroscopy resulted in radial velocities, and hence in a determination of the mass and the distance to the GC derived from the orbital data (R 0 ; Ghez et al 2003Ghez et al , 2005Eisenhauer et al 2003). These results could be improved using other high-velocity Sstars in the vicinity of Sgr A* (e.g.…”

“…However, it is presumed that there are many more fainter stars in the innermost region around Sgr A* to be discovered . The star S2 has a short orbital period of about 16.2 yr which has enabled us to observe it long enough to determine its motion with high accuracy (Ghez et al 2003;Gillessen et al 2009bGillessen et al , 2017. Its velocity at periapse in units of the speed of light is ∼0.02, and if we consider a semimajor axis of 0 .124, an eccentricity of 0.88, and a BH mass of 4 × 10 6 M , then the periapse shift to the lowest order will be around 10 .8 which is large enough to be observable (Jaroszynski 1998;Fragile & Mathews 1999;Rubilar & Eckart 2001;Weinberg et al 2005).…”