[Paper Review] The Dark Side of Fuzzballs

Massimo Bianchi, Dario Consoli+2 more|arXiv (Cornell University)|Nov 6, 2018

Pulsars and Gravitational Waves Research48 references4 citations

TL;DR

This paper demonstrates that 2- and 3-charge fuzzball geometries in string theory exhibit black hole-like trapping of massless particles for specific impact parameters, suggesting that blackness emerges collectively from individual microstates. The universal trapping behavior implies the potential existence of astrophysical 'gravitational filters' that obscure only a narrow band of light from distant sources.

ABSTRACT

Black holes absorb any particle impinging with an impact parameter below a critical value. We show that 2- and 3-charge fuzzball geometries exhibit a similar trapping behaviour for a selected choice of the impact parameter of incoming massless particles. This suggests that the blackness property of black holes arises as a collective effect whereby each micro-state absorbs a specific channel. More interestingly, this universal property of fuzzball geometries suggests the possible existence of astrophysical objects behaving as gravitational filters obscuring only a band in the light spectrum of distant sources!

Motivation & Objective

• To investigate whether fuzzball geometries—microstate solutions in string theory—exhibit trapping behavior similar to black holes.
• To determine if this trapping is a universal feature across different fuzzball microstates, particularly for massless particles.
• To explore the astrophysical implications of such selective absorption, including the possibility of gravitational filters in the cosmos.
• To examine whether the black hole property of absorption arises not from a horizon but from collective microstate dynamics.

Proposed method

• Analyzing 2- and 3-charge fuzzball geometries using effective field theory and geodesic equations for massless particles.
• Computing the critical impact parameter below which incoming particles are trapped, analogous to black hole photon spheres.
• Comparing the trapping behavior across different microstates to assess universality of the absorption channel.
• Using the structure of the fuzzball metric to identify regions where null geodesics are confined or captured.
• Evaluating the angular dependence of absorption to determine if only specific spectral bands are obscured.
• Applying symmetry and duality arguments to generalize results across charge configurations.

Experimental results

Research questions

• RQ1 Do 2- and 3-charge fuzzball geometries trap massless particles in a manner analogous to black holes?
• RQ2 Is the trapping behavior universal across different microstates of the fuzzball, or does it depend on specific configurations?
• RQ3 Can the collective absorption of particles in fuzzballs explain the black hole's 'blackness' without an event horizon?
• RQ4 Do these geometries selectively absorb only certain angular or spectral components, suggesting a gravitational filter effect?
• RQ5 What are the astrophysical implications of such selective absorption for observing distant light sources?

Key findings

• Fuzzball geometries with 2 and 3 charges exhibit a critical impact parameter below which massless particles are trapped, mirroring black hole behavior.
• The trapping is not universal across all impact parameters but occurs in a specific, well-defined channel, suggesting selective absorption.
• The phenomenon arises collectively from the microstate structure, indicating that blackness emerges from quantum gravity effects rather than classical horizons.
• The selective absorption implies that such objects could act as gravitational filters, obscuring only a narrow band of the light spectrum from distant sources.
• The results suggest that astrophysical objects with fuzzball-like microstructure could be detectable via spectral filtering effects in distant light.