LISA constraints on an intermediate-mass black hole in the Galactic Centre

Galactic nuclei are potential hosts for intermediate-mass black holes (IMBHs), whose gravitational field can affect the motion of stars and compact objects. The absence of observable perturbations in our own Galactic Centre has resulted in a few constraints on the mass and orbit of a putative IMBH. Here, we show that the Laser Interferometer Space Antenna (LISA) can further constrain these parameters if the IMBH forms a binary with a compact remnant (a white dwarf, a neutron star, or a stellar-mass black hole), as the gravitational-wave signal from the binary will exhibit Doppler-shift variations as it orbits around Sgr A*. We argue that this method is the most effective for IMBHs with masses 10(3) M-circle dot less than or similar to M-IMBH less than or similar to 10(5) M-circle dot and distances of 0.1-2 mpc with respect to the supermassive black hole, a region of the parameter space partially unconstrained by other methods. We show that in this region the Doppler shift is most likely measurable whenever the binary is detected in the LISA band, and it can help constrain the mass and orbit of a putative IMBH in the centre of our Galaxy. We also discuss possible ways for an IMBH to form a binary in the Galactic Centre, showing that gravitational-wave captures of stellar-mass black holes and neutron stars are the most efficient channel.

Automated summary

Galactic nuclei may harbor intermediate-mass black holes (IMBHs), which can affect the motion of stars and compact objects through their gravitational field. This study demonstrates that the Laser Interferometer Space Antenna (LISA) can provide further constraints on the mass and orbit of putative IMBHs by analyzing the Doppler-shift variations exhibited by the gravitational-wave signal from a binary system with an IMBH and a compact remnant. The authors argue that this method is particularly effective for IMBHs with masses ranging from 10(3) M-circle dot to 10(5) M-circle dot and distances of 0.1-2 mpc from the supermassive black hole, an area of the parameter space that is not well-constrained by other methods.