On the nature of inner light-rings

Understand

Non-singular horizonless ultracompact objects provide a simple resolution to the black holes singularity problem.

• It has been shown that, if these objects are compact enough to exhibit the presence of the light-ring required to mimic the phenomenology of general relativity black holes, they must have at least one additional light-ring.
• The stability of the inner light ring has been proven under the assumption of Einstein equations and the validity of the null energy condition.
• Since this can have important repercussions on the instability of a horizonless ultracompact object and the existence of the latter requires some modified gravitational dynamics and/or exotic matter, it is desirable to obtain a model-independent proof of the stability of the additional light-ring.