[Paper Review] Electromagnetic counterparts to gravitational waves from black hole mergers and naked singularities

Daniele Malafarina, Pankaj S. Joshi|arXiv (Cornell University)|Mar 9, 2016

Pulsars and Gravitational Waves Research3 citations

TL;DR

This paper proposes that the electromagnetic counterpart to the LIGO gravitational wave signal GW150914 may arise from a transient naked singularity formed during binary black hole merger, due to topology change in spacetime. The presence of a short-lived naked singularity would enable far more efficient accretion disk luminosity—exceeding the Eddington limit—than in standard black hole mergers, offering a natural explanation for the high observed luminosity of the Fermi-detected burst.

ABSTRACT

We consider the question here whether the proposed electromagnetic counterpart of the gravitational wave signals in binary black hole coalescence may be due to the appearance of a `short lived' naked singularity during the merger. We point out that the change in topology that the spacetime undergoes during the merger can cause the appearance of a naked singularity. In case some matter, in the form of a small accretion disk, is present in the surroundings of the black hole system then the emitted luminosity during the merger would allow to distinguish the scenario where the naked singularity forms from the scenario where the horizon exists at all times. In fact the emitted luminosity spectrum would be much higher in the case where a naked singularity forms as opposed to the `pure' black hole case. We suggest that the presence of such a transient naked singularity will explain the high luminosity of an electromagnetic counterpart during the merger much more easily.

Motivation & Objective

• To investigate whether the observed high-luminosity electromagnetic counterpart to GW150914 could originate from a transient naked singularity formed during binary black hole merger.
• To examine the role of spacetime topology change in triggering naked singularities during black hole coalescence.
• To compare accretion disk luminosity between black hole and naked singularity scenarios to assess observational distinguishability.
• To explore whether the duration and luminosity of the electromagnetic burst could constrain the lifetime and nature of the transient singularity.
• To assess the potential of such events as observational probes of quantum-gravity effects near singularities.

Proposed method

• Analyzing the implications of topology change in spacetime during black hole mergers, drawing on Geroch and Tipler’s theorems linking topology change to spacetime singularities.
• Applying the Cosmic Censorship Hypothesis and Joshi’s result that topology change implies naked singularities to argue for transient singularity formation during merger.
• Modeling accretion disk luminosity using the standard Eddington limit and relativistic accretion formalism, with special focus on the innermost stable circular orbit (ISCO) and its dependence on the central object’s nature.
• Evaluating the luminosity spectrum for a naked singularity scenario, showing that the absence of an event horizon allows for significantly higher radiative efficiency.
• Estimating required accretion rates for a naked singularity to produce the observed luminosity (~10^49 erg/s) and comparing them to black hole expectations.
• Linking the burst duration to the characteristic timescale of horizon formation and angular momentum dissipation, tied to quantum-gravity scales.

Experimental results

Research questions

• RQ1 Can topology change during a black hole merger lead to the formation of a transient naked singularity?
• RQ2 How does the luminosity of an accretion disk differ between a black hole and a naked singularity scenario?
• RQ3 Can the observed high luminosity of the Fermi GRB associated with GW150914 be explained by a transient naked singularity rather than a black hole?
• RQ4 What accretion rate is required for a naked singularity to produce the observed electromagnetic burst luminosity?
• RQ5 Can the duration of the electromagnetic burst provide constraints on the quantum-gravity scale or the lifetime of the naked singularity?

Key findings

• Topology change during binary black hole merger implies the formation of a naked singularity, as per Geroch and Tipler’s theorems and Joshi’s proof linking topology change to visible singularities.
• The absence of an event horizon in the naked singularity scenario allows for significantly higher accretion disk luminosity, with the luminosity spectrum diverging as the ISCO radius approaches zero.
• A transient naked singularity could produce a luminosity of ~10^49 erg/s with an accretion rate as low as 10^-5 M☉/sec, far below what would be needed for a black hole to reach such luminosity.
• The observed Fermi burst luminosity exceeds the Eddington limit for a 60 M☉ black hole by ten orders of magnitude, making a naked singularity scenario more plausible than extreme accretion onto a black hole.
• The duration of the electromagnetic burst is expected to match the characteristic timescale for horizon formation and angular momentum dissipation, which is tied to quantum-gravity scales.
• Observational comparison of luminosity and burst duration could distinguish between a black hole merger and a transient naked singularity formation, providing a test for quantum-gravity effects.