[Paper Review] Properties of Ultralight Bosons from Spins of Heavy Quasars via Superradiance

Unal, Caner, Pacucci, Fabio+1 more|arXiv (Cornell University)|Dec 23, 2020

Dark Matter and Cosmic PhenomenaPhysics and Astronomy58 citations

TL;DR

This paper uses the Spin-Modified Fundamental Plane (SMFP) with radio, [OIII] luminosity, black hole mass, and spin to derive lower bounds on the spins of 29 heavy, jetted quasars, incorporating relativistic beaming corrections. These spin constraints are then used to probe the parameter space of ultralight bosons (axion-like, dark photons, spin-2 particles) via superradiance, closing a gap in the 10⁻²⁰–10⁻¹⁹ eV range and deriving upper bounds on their decay constants and maximum dark matter fractions.

ABSTRACT

The mass and the spin of accreting and jetted black holes, at the center of Active Galactic Nuclei (AGNs), can be probed by analyzing their electromagnetic spectra. For this purpose, we use the Spin-Modified Fundamental Plane of black hole activity, which non-linearly connects the following four variables (in the source frame): radio luminosity, X-ray or optical luminosity (via the [OIII] emission line), black hole mass and spin. Taking into account the uncertainties in luminosity measurements, conversion factors, relativistic beaming and physical properties of the AGN system, we derive lower bounds on the spins of a group of heavy, jetted AGNs. Using these results, we study the direct implications on the mass spectrum of the ultra-light particles of scalar (axion-like), vector (dark photon) and tensor types (additional spin-2 particles). We close unexplored gap in the parameter space $10^{-20}-10^{-19}$eV. We obtain upper bounds on the axion decay constant (equivalently lower bounds on the self-interaction strength) considering self-interactions could prevent the axion particles entering the instability, and be the reason for non-observation of superradiance. Assuming axion/scalar is described by mass and decay constant, we obtain upper limits on what fraction of dark matter can be formed by ultra-light particles and find that single spieces axion-like light particle can constitute at most $10\%$ of the dark matter in the mass range: $ 10^{-21} < \mu \, (\mathrm{eV}) < 10^{-17}$. Moreover, we derive similar bounds for vector and spin-2 particles and find that light vector fields can constitute at most $10^{-6}$ of the dark matter in $10^{-21}\, \mathrm{eV} < \mu < 10^{-17} \, \mathrm{eV}$ range, and light spin-2 fields can constitute at most $10^{-9}$ of the dark matter in $10^{-23}\, \mathrm{eV} < \mu < 10^{-17} \, \mathrm{eV}$ range.

Motivation & Objective

• To improve the Fundamental Plane of black hole activity by incorporating black hole spin and replacing X-ray luminosity with [OIII] emission line luminosity.
• To derive robust lower bounds on the spins of heavy, jetted active galactic nuclei (AGNs) using multi-wavelength data and relativistic corrections.
• To use these spin constraints to probe the parameter space of ultralight bosons (scalar, vector, tensor) via the superradiance instability.
• To derive upper bounds on axion decay constants and maximum dark matter fractions for ultralight bosons, accounting for self-interactions that could suppress superradiance.
• To close the unexplored parameter space gap in the 10⁻²⁰–10⁻¹⁹ eV mass range for ultralight bosons using observed AGN spins.

Proposed method

• Construct a Spin-Modified Fundamental Plane (SMFP) using radio luminosity, [OIII] line luminosity, black hole mass, and spin (L_radio − L_[OIII] − M − a).
• Incorporate relativistic corrections via the jet bulk Lorentz factor (Γ_j) and viewing angle (θ_j) to improve source-frame luminosity estimates.
• Use 9 AGNs with independently measured spins (via X-ray methods) as calibration points to anchor the SMFP relation.
• Apply the SMFP to 29 jetted quasars to infer conservative lower bounds on their spin parameters using error propagation and uncertainty modeling.
• Use the inferred spin lower bounds to constrain the superradiance instability window for ultralight bosons with masses μ in the 10⁻²³–10⁻¹⁷ eV range.
• Derive upper bounds on axion decay constant f_a from non-observation of superradiance, assuming self-interactions prevent instability.

Experimental results

Research questions

• RQ1 What are the lower bounds on the spin parameters of heavy, jetted quasars using the SMFP with [OIII] luminosity and relativistic corrections?
• RQ2 What is the extent of the previously unexplored parameter space for ultralight bosons (scalar, vector, tensor) in the 10⁻²⁰–10⁻¹⁹ eV mass range?
• RQ3 How do the non-observation of superradiance in these AGNs constrain the axion decay constant f_a and self-interaction strength?
• RQ4 What fraction of dark matter can ultralight scalar, vector, and tensor bosons constitute, given the spin constraints and superradiance bounds?
• RQ5 How do relativistic beaming and viewing angle corrections improve the accuracy of spin and luminosity estimates in the SMFP framework?

Key findings

• The paper closes the unexplored parameter space gap in the 10⁻²⁰–10⁻¹⁹ eV range for ultralight bosons, providing the tightest constraints to date.
• For scalar (axion-like) particles, the maximum contribution to dark matter is 10% in the mass range 10⁻²¹ eV < μ < 10⁻¹⁷ eV, dropping to 0.01–1% at higher masses.
• For vector (dark photon) particles, the maximum contribution to dark matter is 10⁻⁶ in the range 10⁻²¹ eV < μ < 10⁻¹⁹ eV, increasing to 10⁻⁸–10⁻⁶ at higher masses.
• For tensor (spin-2) particles, the maximum contribution to dark matter is 10⁻⁹ in the range 10⁻²³ eV < μ < 10⁻¹⁷ eV.
• The upper bound on the axion decay constant f_a is derived as f_a/M_p ∼ 10⁻⁴ (10¹⁰ yr / τ_BH)¹ᐟ² (10⁻¹³ eV / μ)¹ᐟ² (0.01 / α)⁵ᐟ² (0.9 / a)¹ᐟ², indicating suppression of superradiance by self-interactions.
• The SMFP with [OIII] luminosity and relativistic corrections improves spin inference accuracy, with data points lying within 10% of the plane, validating the method.