Direct Constraints on the Ultralight Boson Mass from Searches of Continuous Gravitational Waves

Superradiance can trigger the formation of an ultralight boson cloud around a spinning black hole. Once formed, the boson cloud is expected to emit a nearly periodic, long-duration, gravitational-wave signal. For boson masses in the range $({10}^{-13}–{10}^{-11})\mathrm{eV}$, and stellar mass black holes, such signals are potentially detectable by gravitational-wave detectors, like Advanced LIGO and Virgo. In this Letter, we present full band upper limits for a generic all-sky search for periodic gravitational waves in LIGO O2 data, and use them to derive—for the first time—direct constraints on the ultralight scalar boson field mass.

Figure 1

Full 95% O2 upper limits on the signal strain amplitude obtained with the frequency-Hough pipeline. Each dot represents the upper limit in a 1-Hz band between 10 and 2048 Hz, computed with the fast procedure described in the text.

Figure 2

95% C.L. exclusion regions in the plane $m_b-M_{\mathrm{BH}}$ assuming a maximum distance $d=1\mathrm{kpc}$ (left plot) and $d=15\mathrm{kpc}$ (right plot), a black hole initial adimensional spin ${\chi }_i=0.998$, and three possible values for $t_{\mathrm{age}}$: $10^3$, $10^6$, $10^8\mathrm{yr}$ (left plot) and $10^3$, $10^{4.5}$, $10^6\mathrm{yr}$ (right plot). The larger light gray area is the accessible parameter space. As expected, the extension of the excluded region decreases for increasing $t_{\mathrm{age}}$ (corresponding to darker color).

Figure 3

95% C.L. exclusion regions in the plane $m_b-M_{\mathrm{BH}}$ assuming a maximum distance $d=1\mathrm{kpc}$ (left plot) and $d=15\mathrm{kpc}$ (right plot), a black hole initial adimensional spin ${\chi }_i=0.6$, and three possible values for $t_{\mathrm{age}}$: $10^3$, ${10}^6$, ${10}^8\mathrm{yr}$ (left plot) and $10^3$, $10^{4.5}$, $10^6\mathrm{yr}$ (right plot). Color code as in previous figure. As expected, the excluded region decreases for increasing $t_{\mathrm{age}}$.