The merger of two galaxies, each hosting a supermassive black hole (SMBH) of mass 10^{6}
We present highprecision radial velocity observations of Gaia BH1, the nearest known black hole (BH). The system contains a solartype G star orbiting a massive dark companion, which could be either a single BH or an inner BH + BH binary. A BH + BH binary is expected in some models where Gaia BH1 formed as a hierarchical triple, which is attractive because they avoid many of the difficulties associated with forming the system through isolated binary evolution. Our observations test the inner binary scenario. We have measured 115 precise RVs of the G star, including 40 from ESPRESSO with a precision of 3–5 m s^{−1}, and 75 from other instruments with a typical precision of 30–100 m s^{−1}. Our observations span 2.33 orbits of the G star and are concentrated near a periastron passage, when perturbations due to an inner binary would be largest. The RVs are wellfit by a Keplerian twobody orbit and show no convincing evidence of an inner binary. Using
 NSFPAR ID:
 10488517
 Publisher / Repository:
 IOP Publishing
 Date Published:
 Journal Name:
 Publications of the Astronomical Society of the Pacific
 Volume:
 136
 Issue:
 1
 ISSN:
 00046280
 Format(s):
 Medium: X Size: Article No. 014202
 Size(s):
 ["Article No. 014202"]
 Sponsoring Org:
 National Science Foundation
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