S62 and S4711: Indications of a Population of Faint Fast-moving Stars inside the S2 Orbit—S4711 on a 7.6 yr Orbit around Sgr A*

Abstract

We present high-pass filtered NACO and SINFONI images of the newly discovered stars S4711–S4715 between 2004 and 2016. Our deep H+K-band (SINFONI) and K-band (NACO) data show the S-cluster star S4711 on a highly eccentric trajectory around Sgr A* with an orbital period of 7.6 yr and a periapse distance of 144 au to the supermassive black hole (SMBH). S4711 is hereby the star with the shortest orbital period and the smallest mean distance to the SMBH during its orbit to date. The used high-pass filtered images are based on coadded data sets to improve the signal to noise. The spectroscopic SINFONI data let us determine detailed stellar properties of S4711 like the mass and the rotational velocity. The faint S-cluster star candidates, S4712–S4715, can be observed in a projected distance to Sgr A* of at least temporarily ≤120 mas. From these stars, S4714 is the most prominent, with an orbital period of 12 yr and an eccentricity of 0.985. The stars S4712–S4715 show similar properties, with magnitudes and stellar masses comparable to those of S4711. The MCMC simulations determine confidently precise uncertainties for the orbital elements of S62 and S4711–S4715. The presence of S4711 in addition to S55, S62, and the also newly found star S4714 implies a population of faint stars that can be found at distances to Sgr A* that are comparable to the size of our solar system. These short orbital time period stars in the dense cluster around the SMBH in the center of our Galaxy are perfect candidates to observe gravitational effects such as the periapse shift.

The Hills Mechanism and the Galactic Center S-stars

“…by vector resonant relaxation Szölgyén & Kocsis 2018, or by scattering between stellar mass black holes and disk binaries Trani et al 2019). We implicitly assume these stars all belong to a single, few Myr-old population, although some admixture of older stars is possible considering (i) only 8 of the 19 stars have spectroscopic age measurements (ii) spectroscopy of recently-discovered, faint S-stars indicate ages closer to ∼ 100 Myr (Peißker et al 2020).…”

On the 2PN Pericentre Precession in the General Theory of Relativity and the Recently Discovered Fast-Orbiting S-Stars in Sgr A*

“…Recently, Peißker et al [13] discovered some short-period S-stars orbiting the candidate supermassive black hole (SMBH) in the Galactic Center (GC) at Sgr A * [24,25]; their relevant orbital parameters are reported in Table 1. Table 1.…”

“…Table 1. Key orbital parameters of some fast-revolving S-stars as per Table 2 of Peißker et al [13]. Here, the semimajor axis a is in milliparsecs (mpc), the orbital period P b is in yr, and the eccentricity e is dimensionless.…”

“…Since some of them can move as fast as 10 percent of the speed of light c at perinigricon, it seems appropriate to look at their 2PN orbital effects. Recently, Peißker et al [13], Fragione and Loeb [26], Iorio [27] investigated the 1PN gravitomagnetic Lense-Thirring orbital precessions induced by the SMBH's angular momentum J • in view of a possible detection in the future. Figure 1 displays the 2PN perinigricon precessionsω 2PN and shifts per orbit ∆ω 2PN of the S-stars S4711, S4714, and S62 as functions of f 0 according to Equation (8).…”

“…Some aspects of the presence of f 0 in Equation 8are discussed in Section 4. Section 5 is devoted to calculating the 2PN pericentre precession for some of the recently discovered fast-orbiting S-stars [13] in the Galactic Center (GC) at Sgr A * . Section 6 summarises the present findings and offers concluding remarks.…”