Exotic Compact Objects and the Fate of the Light-Ring Instability.

Area of Science:

• Astrophysics
• General Relativity
• Theoretical Physics

Background:

• Ultracompact objects with light rings (LRs) but no event horizon can exhibit black hole (BH) like strong gravity.
• The dynamic viability of such horizonless ultracompact objects has been uncertain.
• A stable LR in stationary, axisymmetric ultracompact objects forming from smooth initial data was hypothesized to cause spacetime instability.

Purpose of the Study:

• To investigate the dynamic viability of horizonless ultracompact objects that mimic black holes.
• To determine the development and fate of the spacetime instability triggered by light rings.
• To confirm the role of light ring instability in the evolution of ultracompact objects.

Main Methods:

• Fully nonlinear numerical evolutions of ultracompact bosonic stars.
• Utilizing a novel adiabatic effective potential technique.
• Simulating objects free of other known instabilities to isolate the light ring effect.

Main Results:

• Confirmed that light rings trigger a spacetime instability in ultracompact objects.
• Identified two primary fates for these objects: migration to nonultracompact configurations or collapse into black holes.
• Demonstrated that typical migration or collapse timescales are relatively short (around 10^3 light-crossing times), unless the LR potential well is exceptionally shallow.

Conclusions:

• The light ring instability is an effective mechanism for destroying horizonless ultracompact objects.
• These findings challenge the plausibility of ultracompact objects with light rings as realistic black hole mimics.
• The dynamic evolution of these objects is constrained by the light ring instability, limiting their long-term stability.