Black Hole Superradiance Signatures of Ultralight Vectors (1704.05081v2)

Abstract: The process of superradiance can extract angular momentum and energy from astrophysical black holes (BHs) to populate gravitationally-bound states with an exponentially large number of light bosons. We analytically calculate superradiant growth rates for vectors around rotating BHs in the regime where the vector Compton wavelength is much larger than the BH size. Spin-1 bound states have superradiance times as short as a second around stellar BHs, growing up to a thou- sand times faster than their spin-0 counterparts. The fast rates allow us to use measurements of rapidly spinning BHs in X-ray binaries to exclude a wide range of masses for weakly-coupled spin-1 particles, $5 \times 10^{-14} - 2 \times 10^{-11}$ eV; lighter masses in the range $6 \times 10^{-20} - 2 \times 10^{-17}$ eV start to be constrained by supermassive BH spin measurements at a lower level of confidence. We also explore routes to detection of new vector particles possible with the advent of gravitational wave (GW) astronomy. The LIGO-Virgo collaboration could discover hints of a new light vector particle in statistical analyses of masses and spins of merging BHs. Vector annihilations source continuous monochromatic gravitational radiation which could be observed by current GW observatories. At design sensitivity, Advanced LIGO may measure up to thousands of annihilation signals from within the Milky Way, while hundreds of BHs born in binary mergers across the observable universe may superradiate vector bound states and become new beacons of monochromatic gravitational waves.

• The paper demonstrates that black hole superradiance can amplify ultralight vector fields in as little as one second for stellar-mass black holes.
• It employs spin measurements from X-ray binaries to exclude vector particle masses in the range 5×10⁻¹⁴ to 2×10⁻¹¹ eV, with extended constraints for supermassive black holes.
• The research outlines methods for detecting continuous, monochromatic gravitational waves from vector annihilations, positioning GW observatories as crucial probes for new physics.

Analysis of Black Hole Superradiance Signatures of Ultralight Vectors

The paper on "Black Hole Superradiance Signatures of Ultralight Vectors" delineates the interplay between astrophysical black holes (BHs) and ultralight vector particles through the mechanism of superradiance. This phenomenon facilitates the transfer of angular momentum and energy from a spinning BH to a bound state of bosonic fields, potentially leading to the amplification of fields with exponentially large occupation numbers.

The paper provides detailed analytical results of superradiant growth rates for vector particles with Compton wavelengths that significantly exceed the size of the BH, finding that vector fields (spin-1) can exhibit superradiance times as short as a second for stellar mass BHs — a time scale much shorter than their scalar (spin-0) counterparts. This rapid growth is pivotal in placing constraints on the mass of such vector fields using observations of BHs in X-ray binaries.

The authors exploit spin measurements of rapidly-rotating BHs to exclude masses for weakly-coupled spin-1 particles within the range of $5 \times 10^{-14} - 2 \times 10^{-11}\ \text{eV}$. Additionally, for supermassive BHs, these constraints extend, albeit with lower confidence, into a lighter regime of $6 \times 10^{-20} - 2 \times 10^{-17}\ \text{eV}$.

A significant portion of the paper is devoted to exploring possible detection signals of these vector particles with current and forthcoming gravitational wave (GW) observatories like the LIGO-Virgo collaboration. There is a discussion on the prospects of identifying signatures of new vector particles by examining mass and spin statistics of merging BHs. The gravitational waves emanating from vector annihilations are expected to manifest as continuous monochromatic signals, which could be observed across vast cosmic distances. The paper also predicts that Advanced LIGO, at enhanced sensitivity, could detect countless such events within the Milky Way.

The paper highlights that, regardless of their coupling to the Standard Model, such particles necessarily couple gravitationally, enabling BHs as potential cosmic laboratories for their paper. The dynamics discussed provide insights into BH spin evolution, altered by the exponential growth of vector clouds, thereby influencing current astrophysical observations.

It is apparent that the research traverses potential theoretical and observational frontiers, offering a framework to extend our grasp of beyond the Standard Model physics. The interplay between BH superradiance and ultralight vectors hints at an innovative approach to search for new physics using cosmic structures. Future work may hinge on refining detection capabilities or extending the theoretical models to accommodate other potential ultralight bosonic candidates, thereby enriching the current understanding.

In conclusion, the research underlines the robust capabilities of superradiance as a sensitive probe for ultralight vector particles. The promising numerical results are emblematic of how contemporary theoretical frameworks can leverage experimental and observational astrophysics to decipher constituent particles of the universe that evade detection through conventional means. The observational strategies discussed in the document firmly place gravitational wave astronomy as a crucial frontier for discovering new physics. As our observational apparatuses evolve and improve, the methods and predictions illustrated could transform speculative hypotheses into concrete empirical science, potentially uncovering novel vector particles.