TY - JOUR
T1 - A red giant orbiting a black hole
AU - El-Badry, Kareem
AU - Rix, Hans-Walter
AU - Cendes, Yvette
AU - Rodriguez, Antonio C.
AU - Conroy, Charlie
AU - Quataert, Eliot
AU - Hawkins, Keith
AU - Zari, Eleonora
AU - Hobson, Melissa
AU - Breivik, Katelyn
AU - Rau, Arne
AU - Berger, Edo
AU - Shahaf, Sahar
AU - Seeburger, Rhys
AU - Burdge, Kevin B.
AU - Latham, David W.
AU - Buchhave, Lars A.
AU - Bieryla, Allyson
AU - Bashi, Dolev
AU - Mazeh, Tsevi
AU - Faigler, Simchon
PY - 2023
Y1 - 2023
N2 - We report spectroscopic and photometric follow-up of a dormant black hole (BH) candidate from Gaia DR3. The system, which we call Gaia BH2, contains a ∼1 M⊙ red giant and a dark companion with mass M2=8.9±0.3M⊙ that is very likely a BH. The orbital period, Porb =
1277 d, is much longer than that of any previously studied BH binary.
Our radial velocity (RV) follow-up over a 7-month period spans
>90 per cent of the orbit’s RV range and is in excellent agreement
with the Gaia solution. UV imaging and high-resolution optical
spectra rule out plausible luminous companions that could explain the
orbit. The star is a bright (G = 12.3), slightly metal-poor ([Fe/H]=−0.22) low-luminosity giant (Teff=4600K; R=7.8R⊙; log[g/(cms−2)]=2.6). The binary’s orbit is moderately eccentric (e = 0.52). The giant is enhanced in α-elements, with [α/Fe]=+0.26,
but the system’s Galactocentric orbit is typical of the thin disc. We
obtained X-ray and radio non-detections of the source near periastron,
which support BH accretion models in which the net accretion rate at the
horizon is much lower than the Bondi–Hoyle–Lyttleton rate. At a
distance of 1.16 kpc, Gaia BH2 is the second-nearest known BH, after Gaia BH1. Its orbit – like that of Gaia BH1 – seems too wide to have formed through common envelope evolution. Gaia BH1 and BH2 have orbital periods at opposite edges of the Gaia
DR3 sensitivity curve, perhaps hinting at a bimodal intrinsic period
distribution for wide BH binaries. Dormant BH binaries like Gaia BH1 and Gaia BH2 significantly outnumber their close, X-ray bright cousins, but their formation pathways remain uncertain.
AB - We report spectroscopic and photometric follow-up of a dormant black hole (BH) candidate from Gaia DR3. The system, which we call Gaia BH2, contains a ∼1 M⊙ red giant and a dark companion with mass M2=8.9±0.3M⊙ that is very likely a BH. The orbital period, Porb =
1277 d, is much longer than that of any previously studied BH binary.
Our radial velocity (RV) follow-up over a 7-month period spans
>90 per cent of the orbit’s RV range and is in excellent agreement
with the Gaia solution. UV imaging and high-resolution optical
spectra rule out plausible luminous companions that could explain the
orbit. The star is a bright (G = 12.3), slightly metal-poor ([Fe/H]=−0.22) low-luminosity giant (Teff=4600K; R=7.8R⊙; log[g/(cms−2)]=2.6). The binary’s orbit is moderately eccentric (e = 0.52). The giant is enhanced in α-elements, with [α/Fe]=+0.26,
but the system’s Galactocentric orbit is typical of the thin disc. We
obtained X-ray and radio non-detections of the source near periastron,
which support BH accretion models in which the net accretion rate at the
horizon is much lower than the Bondi–Hoyle–Lyttleton rate. At a
distance of 1.16 kpc, Gaia BH2 is the second-nearest known BH, after Gaia BH1. Its orbit – like that of Gaia BH1 – seems too wide to have formed through common envelope evolution. Gaia BH1 and BH2 have orbital periods at opposite edges of the Gaia
DR3 sensitivity curve, perhaps hinting at a bimodal intrinsic period
distribution for wide BH binaries. Dormant BH binaries like Gaia BH1 and Gaia BH2 significantly outnumber their close, X-ray bright cousins, but their formation pathways remain uncertain.
KW - Binaries: spectroscopic
KW - Stars:blackholes
U2 - 10.1093/mnras/stad799
DO - 10.1093/mnras/stad799
M3 - Journal article
SN - 0035-8711
VL - 521
SP - 4323
EP - 4348
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 3
ER -