Observational signatures of hot spots orbiting horizonless objects

Understand

Pushed by a number of advances, electromagnetic observatories have now reached the horizon scale of supermassive black holes.

• The existence and properties of horizons in our universe is one of the outstanding fundamental issues that can now be addressed.
• Here we investigate the ability to discriminate between black holes and compact, horizonless objects, focusing on the lensing of hot spots around compact objects.
• We work in particular with boson and Proca stars as central objects, and show that the absence of a horizon gives rise to a characteristic feature -- photons that plough through the central object and produce an extra image.