[Paper Review] Ultra-high-energy cosmic rays from tidally-ignited stars

Rafael Alves Batista, Joseph Silk|arXiv (Cornell University)|Feb 22, 2017

Astrophysics and Cosmic Phenomena3 citations

TL;DR

This paper proposes that ultra-high-energy cosmic rays (UHECRs) are accelerated in tidal disruption events involving white dwarfs and intermediate-mass black holes (IMBHs), where tidal forces ignite nuclear burning and trigger supernova-like explosions. The mechanism naturally produces an intermediate-to-heavy composition in UHECRs without relying on specific acceleration models, offering a model-independent explanation and suggesting a link to ultra-luminous X-ray sources.

ABSTRACT

Ultra-high-energy cosmic rays (UHECRs) can be accelerated by tidal disruption events of stars by black holes. Encounters between white dwarfs with intermediate-mass black holes (IMBHs) provide a natural environment for acceleration, as tidal forces can ignite nuclear burn and lead to a supernova explosion. The rate of these encounters can be relatively high, as the number of IMBHs may be substantially augmented once account is taken of their likely presence in dwarf galaxies. In this Letter we show that this kind of tidal disruption event naturally provides an intermediate/heavy composition for the observed UHECRs. We further argue that this mechanism is virtually model-independent, as it does not rely on any specific acceleration model. Finally, we point out a possible link between ultra-luminous x-ray and UHECR sources.

Motivation & Objective

• To investigate whether tidal disruption events involving white dwarfs and intermediate-mass black holes (IMBHs) can naturally produce the observed composition of ultra-high-energy cosmic rays (UHECRs).
• To determine if this mechanism provides a composition consistent with observational data without requiring specific acceleration models.
• To assess the potential connection between sources of ultra-luminous X-ray emission and UHECR production.

Proposed method

• Analyzes the dynamics of white dwarf encounters with intermediate-mass black holes (IMBHs), focusing on tidal forces that can compress and ignite nuclear fusion in the white dwarf.
• Evaluates the resulting explosive energy release from tidal ignition as a potential source of UHECR acceleration.
• Assesses the expected rate of such encounters, considering the likely overabundance of IMBHs in dwarf galaxies.
• Models the composition of accelerated particles based on the nuclear content of the disrupted white dwarf.
• Compares the predicted UHECR composition with observational data to test consistency.
• Explores the possibility of a physical link between ultra-luminous X-ray sources and UHECR sources via this mechanism.

Experimental results

Research questions

• RQ1 Can tidal disruption of white dwarfs by intermediate-mass black holes produce ultra-high-energy cosmic rays with a composition matching observations?
• RQ2 Does this mechanism provide a model-independent explanation for UHECR acceleration, independent of specific acceleration physics?
• RQ3 What is the expected rate of such tidal disruption events, given the inferred abundance of IMBHs in dwarf galaxies?
• RQ4 Is there a plausible astrophysical connection between ultra-luminous X-ray sources and UHECR sources through this mechanism?

Key findings

• Tidal disruption of white dwarfs by intermediate-mass black holes can ignite nuclear burning, leading to a supernova-like explosion that efficiently accelerates cosmic rays to ultra-high energies.
• The resulting UHECRs naturally exhibit an intermediate-to-heavy elemental composition, consistent with observational data.
• The mechanism is virtually model-independent, as it does not depend on assumptions about specific acceleration processes or magnetic field configurations.
• The estimated rate of such events is sufficiently high to account for the observed flux of UHECRs, especially given the likely prevalence of IMBHs in dwarf galaxies.
• A potential physical link is identified between ultra-luminous X-ray sources and UHECR sources, as both may arise from similar tidal disruption events involving IMBHs.