The Keplerian three-body encounter I. Insights on the origin of the S-stars and the G-objects in the Galactic center

Abstract

Recent spectroscopic analysis has set an upper limit to the age of the S-stars, the ~30 B-type stars in highly eccentric orbits around the supermassive black hole (SMBH) in the Galactic center. The inferred age (<15 Myr) is in tension with the binary break-up scenario proposed to explain their origin. However, the new estimate is compatible with the age of the disk of O-type stars that lies at a farther distance from the SMBH. Here we investigate a new formation scenario, assuming that both S-stars and the O-type stars were born in the same disk around SgrA*. We simulate encounters between binaries of the stellar disk and stellar black holes from a dark cusp around SgrA*. We find that B-type binaries can be easily broken up by the encounters and their binary components are kicked into highly eccentric orbits around the SMBH. In contrast, O-type binaries are less frequently disrupted and their members remain in low eccentricity orbits. This mechanism can reproduce 12 S-stars just by assuming that the binaries initially lie within the stellar disk as observed nowadays. To reproduce all the S-stars, the original disk must have been extended down to 0.006 pc. However in this case many B- and O-type stars remain in low eccentricity orbits below 0.03 pc, in contrast with the observations. Therefore, some other mechanism is necessary to disrupt the disk below 0.03 pc. This scenario can also explain the high eccentricity of the G-objects, if they have a stellar origin.