[Paper Review] Fast Radio Bursts from neutron stars plunging into black holes

Sudip Bhattacharyya|arXiv (Cornell University)|Nov 24, 2017

Pulsars and Gravitational Waves Research33 references6 citations

TL;DR

This paper proposes that fast radio bursts (FRBs) originate from giant radio pulses emitted by neutron stars that rapidly spin up as they plunge into spinning black holes. The model explains FRB luminosity, timescale, and non-repeating nature via spin-up-induced emission, predicts simultaneous gravitational waves from nearby mergers, and implies strong gravity effects like frame-dragging and event horizons.

ABSTRACT

Fast radio bursts (FRBs) are millisecond-duration intense radio flares occurring at cosmological distances. Many models have been proposed to explain these topical astronomical events, but none has so far been confirmed. Here we show that a novel way involving enhanced giant radio pulses from a rapidly spun-up neutron star near a spinning black hole can explain the main properties of non-repeating FRBs. Independent observations of such pulses, which are not enhanced, from some Galactic pulsars make our model reliable. If correct, our model would imply the existence of event horizons, the Lense-Thirring effect, and a significant spin energy extraction from a black hole. Moreover, an FRB would then probe the pulsar magnetosphere and its emission, and map the strong gravity region near a black hole. Besides, our model predicts simultaneous detections of FRBs and gravitational waves from black hole -- neutron star mergers for fortuitously nearby FRB events.

Motivation & Objective

• Explain the high radio luminosity and millisecond timescale of non-repeating FRBs using a mechanism not reliant on unverified emission processes.
• Address the lack of associated emission in other wavelengths by linking FRBs to giant radio pulses from neutron stars.
• Provide a physically plausible mechanism that accounts for the non-repeating nature of most FRBs through black hole–neutron star merger dynamics.
• Establish a connection between FRBs and detectable gravitational waves from nearby black hole–neutron star mergers.
• Demonstrate that the model can explain observed FRB properties using independently verified phenomena like giant pulses from Galactic pulsars.

Proposed method

• Model the spin-up of a neutron star due to Lense-Thirring precession as it approaches the innermost stable circular orbit (ISCO) of a spinning black hole.
• Use the spin-precession frequency formula for a point gyroscope to estimate the neutron star's rotational frequency evolution during inspiral.
• Calculate the luminosity of giant radio pulses based on the neutron star's increasing spin frequency and known magnetic field strength (e.g., Crab-like B = 3.79×10¹² G).
• Assess the emission timescale by considering the intrinsic width of the pulse, derived from the spin-up timescale and the observed FRB duration.
• Estimate the expected event rate of such FRB events and compare it with observed FRB rates and predicted black hole–neutron star merger rates.
• Predict coincident gravitational wave signals from the final merger phase, assuming fortuitous proximity for detection.

Experimental results

Research questions

• RQ1 Can giant radio pulses from a rapidly spun-up neutron star near a black hole explain the extreme luminosity and short duration of non-repeating FRBs?
• RQ2 Does the spin-up mechanism via Lense-Thirring precession naturally account for the non-repeating nature of most FRBs?
• RQ3 Can this model predict detectable gravitational wave signals coincident with FRB events, providing a testable signature?
• RQ4 How does the spin-up process affect the emission properties of the neutron star’s magnetosphere, and is this consistent with observed FRB fluence and dispersion measures?
• RQ5 Is the event rate of such FRB-producing systems consistent with the observed FRB rate of ~10³ Gpc⁻³ yr⁻¹?

Key findings

• The model explains the intrinsic peak flux density of FRBs exceeding 1120 Jy and luminosities above 6.8×10⁴⁴ erg s⁻¹, consistent with observed FRB 150807.
• Rapid spin-up of the neutron star due to Lense-Thirring precession increases the giant pulse luminosity, accounting for the high observed radio brightness temperature (~10³⁵ K).
• The non-repeating nature of FRBs is naturally explained by the final plunge and merger of the neutron star into the black hole, terminating the emission process.
• The model predicts that FRBs from nearby black hole–neutron star mergers would be accompanied by detectable gravitational wave signals, offering a key observational test.
• The estimated FRB event rate of ~10³ Gpc⁻³ yr⁻¹ is consistent with optimistic estimates of black hole–neutron star merger rates, supporting the model’s plausibility.
• The mechanism implies the existence of event horizons, the Lense-Thirring effect, and significant spin energy extraction from the black hole, providing strong gravity diagnostics.