TY - JOUR

T1 - A Hidden Friend for the Galactic Center Black Hole, Sgr A*

AU - Naoz, Smadar

AU - Will, Clifford M.

AU - Ramirez-Ruiz, Enrico

AU - Hees, Aurelien

AU - Ghez, Andrea M.

AU - Do, Tuan

PY - 2020/1/1

Y1 - 2020/1/1

N2 - The hierarchical nature of galaxy formation suggests that a supermassive black hole binary could exist in our galactic center. We propose a new approach to constraining the possible orbital configuration of such a binary companion to the galactic center black hole Sagittarius A* (Sgr A*) through the measurement of stellar orbits. Focusing on the star S0-2, we show that requiring its orbital stability in the presence of a companion to Sgr A* yields stringent constraints on the possible configurations of such a companion. Furthermore, we show that precise measurements of time variations in the orbital parameters of S0-2 could yield stronger constraints. Using existing data on S0-2 we derive upper limits on the binary black hole separation as a function of the companion mass. For the case of a circular orbit, we can rule out a 10(5) M companion with a semimajor axis greater than 170 au or 0.8 mpc. This is already more stringent than bounds obtained from studies of the proper motion of Sgr A*. Including other stars orbiting the galactic center should yield stronger constraints that could help uncover the presence of a companion to Sgr A*. We show that a companion can also affect the accretion process, resulting in a variability that may be consistent with the measured infrared flaring timescales and amplitudes. Finally, if such a companion exists, it will emit gravitational wave radiation, potentially detectable with the Laser Interferometer Space Antenna (LISA).

AB - The hierarchical nature of galaxy formation suggests that a supermassive black hole binary could exist in our galactic center. We propose a new approach to constraining the possible orbital configuration of such a binary companion to the galactic center black hole Sagittarius A* (Sgr A*) through the measurement of stellar orbits. Focusing on the star S0-2, we show that requiring its orbital stability in the presence of a companion to Sgr A* yields stringent constraints on the possible configurations of such a companion. Furthermore, we show that precise measurements of time variations in the orbital parameters of S0-2 could yield stronger constraints. Using existing data on S0-2 we derive upper limits on the binary black hole separation as a function of the companion mass. For the case of a circular orbit, we can rule out a 10(5) M companion with a semimajor axis greater than 170 au or 0.8 mpc. This is already more stringent than bounds obtained from studies of the proper motion of Sgr A*. Including other stars orbiting the galactic center should yield stronger constraints that could help uncover the presence of a companion to Sgr A*. We show that a companion can also affect the accretion process, resulting in a variability that may be consistent with the measured infrared flaring timescales and amplitudes. Finally, if such a companion exists, it will emit gravitational wave radiation, potentially detectable with the Laser Interferometer Space Antenna (LISA).

KW - Supermassive black holes

KW - Astrophysical black holes

KW - Galactic center

KW - the Milky Way physics

KW - Gravitation

KW - Gravitational waves

KW - Gravitational wave sources

KW - the Milky Way

KW - Milky Way dynamics

KW - STELLAR ORBITS

KW - BINARY

KW - MODEL

KW - VARIABILITY

KW - HYPERVELOCITY

KW - PARSEC

KW - STARS

KW - MILKY

KW - MASS

KW - DISCOVERY

U2 - 10.3847/2041-8213/ab5e3b

DO - 10.3847/2041-8213/ab5e3b

M3 - Letter

VL - 888

JO - The Astrophysical Journal Letters

JF - The Astrophysical Journal Letters

SN - 2041-8205

IS - 1

M1 - 8

ER -