Myers-Perry black holes with scalar hair and a mass gap: unequal spins

TL;DR

This paper constructs five-dimensional rotating black holes with scalar hair, revealing new solutions with unequal spins, a mass gap, and connections to boson stars and singly spinning black holes, expanding understanding of black hole scalar hair.

Contribution

It introduces fully non-linear solutions of Myers-Perry black holes with scalar hair in five dimensions, including cases with unequal angular momenta and a mass gap, which were not previously known.

Findings

Existence of regular, asymptotically flat black holes with scalar hair.

Solutions reduce to boson stars or extremal black holes in certain limits.

Presence of a mass gap preventing continuous deformation from vacuum black holes.

Abstract

We construct rotating boson stars and Myers-Perry black holes with scalar hair (MPBHsSH) as fully non-linear solutions of five dimensional Einstein gravity minimally coupled to a complex, massive scalar field. The MPBHsSH are, in general, regular on and outside the horizon, asymptotically flat, and possess angular momentum in a single rotation plane. They are supported by rotation and have no static limit. Such hairy BHs may be thought of as bound states of boson stars and singly spinning, vacuum MPBHs and inherit properties of both these building blocks. When the horizon area shrinks to zero, the solutions reduce to (in a single plane) rotating boson stars; but the extremal limit also yields a zero area horizon, as for singly spinning MPBHs. Similarly to the case of equal angular momenta, and in contrast to Kerr black holes with scalar hair, singly spinning MPBHsSH are disconnected from the vacuum black holes, due to a mass gap. We observe that for the general case, with two unequal angular momenta, the equilibrium condition for the existence of MPBHsSH is $w=m_1\Omega_1+m_2\Omega_2$, where $\Omega_i$ are the horizon angular velocities in the two independent rotation planes and $w,m_i$, $i=1,2$, are the scalar field's frequency and azimuthal harmonic indices.