Superradiance in stars

Cardoso, Vítor; Brito, Richard; Rosa, João Luís

doi:10.1103/physrevd.91.124026

Cited by 43 publications

(40 citation statements)

References 25 publications

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“…However, superradiant effects are not limited to rotating black holes and in fact can appear in any classical system that is able to absorb radiation [12,14,15,22,33,34]. In this work, we show that superradiance also occurs in the presence of rotating and conducting spheres, and most notably in (rotating) stars with nonzero conductivity.…”

Section: Superradiance In Starsmentioning

confidence: 66%

Superradiance in rotating stars and pulsar-timing constraints on dark photons

Cardoso

Pani

2017

Phys. Rev. D

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In the presence of massive bosonic degrees of freedom, rotational superradiance can trigger an instability that spins down black holes. This leads to peculiar gravitational-wave signatures and distribution in the spin-mass plane, which in turn can impose stringent constraints on ultralight fields. Here, we demonstrate that there is an analogous spindown effect for conducting stars. We show that rotating stars amplify low frequency electromagnetic waves, and that this effect is largest when the time scale for conduction within the star is of the order of a light crossing time. This has interesting consequences for dark photons, as massive dark photons would cause stars to spin down due to superradiant instabilities. The time scale of the spindown depends on the mass of the dark photon, and on the rotation rate, compactness, and conductivity of the star. Existing measurements of the spindown rate of pulsars place direct constraints on models of dark sectors. Our analysis suggests that dark photons of mass mV ∼ 10 −12 eV are excluded by pulsar-timing observations. These constraints also exclude superradiant instabilities triggered by dark photons as an explanation for the spin limit of observed pulsars.

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Section: Superradiance In Starsmentioning

confidence: 66%

Superradiance in rotating stars and pulsar-timing constraints on dark photons

Cardoso

Pani

2017

Phys. Rev. D

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“…equation (2a). Such term was indeed used by Zel'dovich in his seminal study and can be shown to mimic accurately the correct description of many superradiant systems [32][33][34][35]. Such a Lorentz-invariance-violating term introduces a superradiantlike instability, with a timescale on the order 1=C, which we can tune to be within our numerical limits.…”

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confidence: 71%

Blasts of Light from Axions

2019

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The nature of dark matter is one of the longest-standing puzzles in science. Axions or axionlike particles are a key possibility and arise in mechanisms to solve the strong CP problem, but also in low-energy limits of string theory. Extensive experimental and observational efforts are actively looking for "axionic" imprints. Independent of their nature, abundance, and contribution to the dark matter problem, axions form dense clouds around spinning black holes, grown by superradiant mechanisms. It was recently suggested that once couplings to photons are considered, an exponential (quantum) stimulated emission of photons ensues at large enough axion number. Here we solve numerically the classical problem in different setups. We show that laserlike emission from clouds exists at the classical level, and we provide the first quantitative description of the problem.

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“…Finally, we have focused solely on scattering in this work, but it is well known that superradiance can also manifest as an instability that triggers the exponential growth of bound states around Kerr black holes [37][38][39][40][41][42][43][44][45] and other astrophysical bodies [12,13,46]. A similar instability is likely to be present in black hole binaries and will be the subject of a forthcoming paper.…”

Section: Discussionmentioning

confidence: 99%

“…Case in point: In his seminal papers on the subject [8,9], Zel'dovich describes the amplification of electromagnetic waves by a conducting cylinder; while more recently, Torres et al reported the first laboratory observation of superradiance in water waves scattered by a draining vortex [10]. Superradiant scattering by rotating stars has also recently been studied [11][12][13].…”

Section: Introductionmentioning

confidence: 99%

Superradiant scattering by a black hole binary

Wong

2019

Phys. Rev. D

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I present evidence of a novel guise of superradiance that arises in black hole binary spacetimes. Given the right initial conditions, a wave will be amplified as it scatters off the binary. This process, which extracts energy from the orbital motion, is driven by absorption across the horizons and is most pronounced when the individual black holes are not spinning. Focusing on real scalar fields, I demonstrate how modern effective field theory (EFT) techniques enable the computation of the superradiant amplification factor analytically when there exist large separations of scales. Although exploiting these hierarchies inevitably means that the amplification factor is always negligible (it is never larger than about one part in 10 10) in the EFT's regime of validity, this work has interesting theoretical implications for our understanding of general relativity and lays the groundwork for future studies on superradiant phenomena in binary systems.

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Superradiance in stars

Cited by 43 publications

References 25 publications

Superradiance in rotating stars and pulsar-timing constraints on dark photons

Superradiance in rotating stars and pulsar-timing constraints on dark photons

Blasts of Light from Axions

Superradiant scattering by a black hole binary

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