Projects per year
Abstract
The "nohair" theorem states that astrophysical black holes are fully characterized by just two numbers: their mass and spin. The gravitationalwave emission from a perturbed blackhole consists of a superposition of damped sinusoids, known as quasinormal modes. Quasinormal modes are specified by three integers (m,n): the (m) integers describe the angular properties and (n) specifies the (over)tone. If the nohair theorem holds, the frequencies and damping times of quasinormal modes are determined uniquely by the mass and spin of the black hole, while phases and amplitudes depend on the particular perturbation. Current tests of the nohair theorem attempt to identify these modes in a semiagnostic way, without imposing priors on the source of the perturbation. This is usually known as blackhole spectroscopy. Applying this framework to GW150914, the measurement of the first overtone led to the confirmation of the theorem to 20% level. We show, however, that such semiagnostic tests cannot provide strong evidence in favor of the nohair theorem, even for extremely loud signals, given the increasing number of overtones (and free parameters) needed to fit the data. This can be solved by imposing prior assumptions on the origin of the perturbed black hole that can further constrain the explored parameters: in particular, our knowledge that the ringdown is sourced by a binary blackhole merger. Applying this strategy to GW150914, we find a natural log Bayes factor of ∼6.5 in favor of the Kerr nature of its remnant, indicating that the hairy object hypothesis is disfavored with <1:600 with respect to the Kerr blackhole one.
Original language  English 

Article number  024041 
Number of pages  12 
Journal  Physical Review D 
Volume  103 
Issue number  2 
DOIs  
Publication status  Published  15 Jan 2021 

ARC Centre of Excellence for Gravitational Wave Discovery
Bailes, M., McClelland, D. E., Levin, Y., Blair, D. G., Scott, S. M., Ottaway, D. J., Melatos, A., Veitch, P. J., Wen, L., Shaddock, D. A., Slagmolen, B. J. J., Zhao, C., Evans, R. J., Ju, L., Galloway, D., Thrane, E., Hurley, J. R., Coward, D. M., Cooke, J., Couch, W., Hobbs, G. B., Reitze, D., Rowan, S., Cai, R., Adhikari, R. X., Danzmann, K., Mavalvala, N., Kulkarni, S. R., Kramer, M., Branchesi, M., Gehrels, N., Weinstein, A. J. R., Steeghs, D., Bock, D. & Lasky, P.
Monash University – Internal University Contribution, Monash University – Internal Department Contribution
1/01/17 → 31/03/24
Project: Research

Putting Einstein to the Test: Probing Gravity with Gravitational Waves
1/05/18 → 31/12/20
Project: Research

Extreme astrophysics in the age of gravitational waves
Australian Research Council (ARC), Monash University
30/06/17 → 18/11/21
Project: Research