Simulating the Galactic population of axion clouds around stellar-origin black holes: Gravitational wave signals in the 10-100 kHz band

• Published in: arXiv.org
• Main Authors: Sprague, Jacob R, Larson, Shane L, Wang, Zhiyuan, Klomp, Shelby, Laeuger, Andrew, Winstone, George, Aggarwal, Nancy, Geraci, Andrew A, Kalogera, Vicky
• Format: Paper
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 28.10.2024
• Subjects: Astronomical models; Gravitational waves; Hypothetical particles; Noise sensitivity; Scalars; Sensitivity analysis; Stellar age

Ultralight scalar fields can experience runaway `superradiant' amplification near spinning black holes, resulting in a macroscopic `axion cloud' which slowly dissipates via continuous monochromatic gravitational waves. For a particular range of boson masses, \(\mathcal{O}(10^{-11}\) -- \(10^{-10})\) eV, an axion cloud will radiate in the \(10\) -- \(100\) kHz band of the Levitated Sensor Detector (LSD). Using fiducial models of the mass, spin, and age distributions of stellar-origin black holes, we simulate the present-day Milky Way population of these hypothetical objects. As a first step towards assessing the LSD's sensitivity to the resultant ensemble of GW signals, we compute the corresponding signal-to-noise ratios which build up over a nominal integration time of \(10^{7}\) s, assuming the projected sensitivity of the \(1\)-m LSD prototype currently under construction, as well as for future \(10\)-m and \(100\)-m concepts. For a \(100\)-m cryogenic instrument, hundreds of resolvable signals could be expected if the boson mass \(\mu\) is around \(3\times10^{-11}\) eV, and this number diminishes with increasing \(\mu\) up to \(\approx 5.5\times10^{-11}\) eV. The much larger population of unresolved sources will produce a confusion foreground which could be detectable by a \(10\)-m instrument if \(\mu \in (3-4.5)\times10^{-11}\) eV, or by a \(100\)-m instrument if \(\mu \in (3-6)\times10^{-11}\) eV.