Viability of light-boson hairy black holes

Ascertain whether the mass parameter space for ultralight bosons that source scalar/vector hair around black holes will be entirely closed by observations, and whether additional families of hairy rotating black holes remain conceivable and astrophysically relevant.

Background

Ultralight bosons (scalars/vectors) can form clouds around spinning black holes through superradiance, yielding hairy solutions and observable signatures. However, pulsar timing arrays and superradiance constraints are increasingly restricting their mass range.

Determining the fate of this parameter space and the existence of further solutions impacts both particle physics and astrophysics.

References

Open questions: Will the mass parameter space for these light bosons close in due time? Are additional hairy rotating black hole solutions still conceivable and relevant astrophysically?

— Black Holes Inside and Out 2024: visions for the future of black hole physics  (2410.14414 - Afshordi et al., 2024) in Enrico Barausse, Section "GR with known/unkown fields"

Whether it evolves into such a solution, however, cannot be determined within the present framework.

— Dark-to-black super-accretion as a spin-imprinting mechanism for supermassive Kerr black holes  (2608.24432 - Fakhry et al., 25 Aug 2026) in Section Conclusions, paragraph beginning “It is important to remark again on the nature of the endpoint”

A detailed investigation of their phenomenological properties, including Hawking radiation, is left for future work.

— Cosmological implications for hairy black holes via spontaneous symmetry breaking: Are Hairy Black Holes Primordial?  (2609.02102 - Das et al., 2 Sep 2026) in Introduction; Section 7, Summary and Conclusion

An interesting extension of our current scenario would be to introduce a sufficiently large bare mass term, in which case coherent scalar-field oscillations at later epochs could constitute a dark-matter component . Such a mass term, if strong enough, could also significantly modify the hairy black hole solutions . Furthermore, an explicit symmetry-breaking term could induce nontrivial dynamics along the angular or phase direction $\theta$ of the complex scalar field, potentially providing a mechanism for baryogenesis . We leave a detailed investigation of these possibilities, and of the broader interplay between cosmological dynamics and black hole phenomenology within a unified modified-gravity framework for future work.

— Cosmological implications for hairy black holes via spontaneous symmetry breaking: Are Hairy Black Holes Primordial?  (2609.02102 - Das et al., 2 Sep 2026) in Section 7, Summary and Conclusion