Search for continuous gravitational wave emission from the Milky Way center in O3 LIGO-Virgo data

We present a directed search for continuous gravitational wave (CW) signals emitted by spinning neutron stars located in the inner parsecs of the Galactic Center (GC). Compelling evidence for the presence of a numerous population of neutron stars has been reported in the literature, turning this region into a very interesting place to look for CWs. In this search, data from the full O3 LIGO-Virgo run in the detector frequency band $[10,2000]\mathrm{Hz}$ have been used. No significant detection was found and 95% confidence level upper limits on the signal strain amplitude were computed, over the full search band, with the deepest limit of about $7.6\times {10}^{-26}$ at $\simeq 142\mathrm{Hz}$. These results are significantly more constraining than those reported in previous searches. We use these limits to put constraints on the fiducial neutron star ellipticity and r-mode amplitude. These limits can be also translated into constraints in the black hole mass–boson mass plane for a hypothetical population of boson clouds around spinning black holes located in the GC.

Figure 1

Parameter space investigated in this search (see Sec. 3a). The sky position is that of Sgr A*, while frequency and spin down span the ranges given on the axes.

Figure 2

Estimates of the 95% CL strain upper limits, derived for the best combination HL in 1-Hz bands [72].

Figure 3

Estimates of the 95% CL ellipticity upper limits assuming a GC distance of 8 kpc. The shaded area between the two curves covers the possible values of the moment of inertia along z of the spinning star. The lower curve corresponds to a moment of inertia 5 times larger than the fiducial value $I_{\mathrm{fid}}$, sustainable by exotic objects.

Figure 4

Estimates of the 95% CL r-mode amplitude upper limits for neutron stars in the GC region assuming $d=8\mathrm{kpc}$.

Figure 5

Constraints on the black hole mass–boson mass plane, assuming CW emission from boson clouds around spinning black holes located in the GC. An initial black hole dimensionless spin ${\chi }_i=0.5$ and cloud ages of $t_{\mathrm{age}}={10}^3,{10}^5,{10}^7\mathrm{yr}$ are considered. The reported exclusion regions have been derived from the upper limits in [72].