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#### Multimode Quasinormal Spectrum from a Perturbed Black Hole

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2105.05238.pdf

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PhysRevLett.131.221402.pdf

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##### Citation

Capano, C., Cabero, M., Abedi, J., Kastha, S., Westerweck, J., Nitz, A. H., et al. (2023).
Multimode Quasinormal Spectrum from a Perturbed Black Hole.* Physical Review Letters,* *131*(22): 221402. doi:10.1103/PhysRevLett.131.221402.

Cite as: https://hdl.handle.net/21.11116/0000-0008-8E24-0

##### Abstract

We provide strong observational evidence for a multimode black hole ringdown

spectrum, using the gravitational wave event GW190521. We show strong evidence

for the presence of at least two ringdown modes, with a Bayes factor of

$43.4^{+8.1}_{-6.8}$ preferring two modes over one. The dominant mode is the

fundamental $\ell=m=2$ harmonic, and the sub-dominant mode corresponds to the

fundamental $\ell=m=3$ harmonic. We estimate the redshifted mass and

dimensionless spin of the final black hole as $332^{+31}_{-35}\,M_\odot$ and

$0.871^{+0.052}_{-0.096}$ respectively. The detection of the two modes

disfavors a binary progenitor with equal masses, and the mass ratio is

constrained to $0.45^{+0.22}_{-0.29}$. General relativity predicts that the

frequency and damping time of each mode in the spectrum depends only on two

parameters, the black hole mass and angular momentum. Consistency between the

different modes thus provides a test of general relativity. As a test of the

black hole no-hair theorem, we constrain the fractional deviation of the

sub-dominant mode frequency from the Kerr prediction to $\delta f_{330} =

-0.010^{+0.073}_{-0.121}$

spectrum, using the gravitational wave event GW190521. We show strong evidence

for the presence of at least two ringdown modes, with a Bayes factor of

$43.4^{+8.1}_{-6.8}$ preferring two modes over one. The dominant mode is the

fundamental $\ell=m=2$ harmonic, and the sub-dominant mode corresponds to the

fundamental $\ell=m=3$ harmonic. We estimate the redshifted mass and

dimensionless spin of the final black hole as $332^{+31}_{-35}\,M_\odot$ and

$0.871^{+0.052}_{-0.096}$ respectively. The detection of the two modes

disfavors a binary progenitor with equal masses, and the mass ratio is

constrained to $0.45^{+0.22}_{-0.29}$. General relativity predicts that the

frequency and damping time of each mode in the spectrum depends only on two

parameters, the black hole mass and angular momentum. Consistency between the

different modes thus provides a test of general relativity. As a test of the

black hole no-hair theorem, we constrain the fractional deviation of the

sub-dominant mode frequency from the Kerr prediction to $\delta f_{330} =

-0.010^{+0.073}_{-0.121}$