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 on 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 breakup 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 . However, in this case many B- and O-type stars remain in low-eccentricity orbits below , in contrast with the observations. Therefore, some other mechanism is necessary to disrupt the disk below . This scenario can also explain the high eccentricity of the G-objects, if they have a stellar origin.