Testing Gravity with Pulsars in the SKA Era (1501.00058v1)

Abstract: The Square Kilometre Array (SKA) will use pulsars to enable precise measurements of strong gravity effects in pulsar systems, which yield tests of gravitational theories that cannot be carried out anywhere else. The Galactic census of pulsars will discover dozens of relativistic pulsar systems, possibly including pulsar -- black hole binaries which can be used to test the "cosmic censorship conjecture" and the "no-hair theorem". Also, the SKA's remarkable sensitivity will vastly improve the timing precision of millisecond pulsars, allowing probes of potential deviations from general relativity (GR). Aspects of gravitation to be explored include tests of strong equivalence principles, gravitational dipole radiation, extra field components of gravitation, gravitomagnetism, and spacetime symmetries.

Testing Gravity with Pulsars in the SKA Era

This paper provides a comprehensive exploration of the potential to test general relativity (GR) and alternative theories of gravity using pulsars, especially in light of the advancements anticipated with the Square Kilometre Array (SKA). The research highlights the ability of the SKA to significantly enhance our understanding of gravitational phenomena, particularly in regions of strong gravitational fields.

Pulsars as Tools for Testing Gravity

Pulsars, particularly those in binary systems, have a remarkable capacity for testing the limits of gravitational theories. Their emission of regular radio pulses allows for precise timing analyses, making them potent tools for studying gravitational effects in strong-field regimes. These regimes are particularly important for investigating deviations from GR, as they provide scenarios where alternative theories of gravity may demonstrate measurable differences.

Implications of the SKA on Pulsar Timing

The SKA's unprecedented sensitivity and resolution will significantly improve the timing precision of millisecond pulsars. This enhancement will allow for a more profound investigation into potential deviations from GR, including:

1. Tests of Strong Equivalence Principles: The SKA will facilitate precise measurements that challenge the validity of the strong equivalence principle by observing differential accelerations that violate the universality of free fall among pulsars with varying gravitational bindings.
2. Gravitational Dipole Radiation: The SKA's capabilities will permit stringent constraints on gravitational dipole emissions that arise in many alternative theories of gravity, such as scalar-tensor theories that introduce additional field components.
3. Gravitomagnetism and Geodetic Precession: Enhanced precision will enable detailed examinations of gravitomagnetic effects, such as geodetic precession observed in binary pulsar systems, offering insights into the spin-curvature interactions predicted by GR.

Relativistic Binary Systems and Advanced Tests

The paper discusses how the SKA is expected to discover numerous relativistic binary systems, including neutron star-neutron star (NS-NS) and potentially neutron star-black hole (NS-BH) binaries. These systems will be instrumental in:

• Testing the "No-Hair Theorem" and "Cosmic Censorship Conjecture": Pulsar-black hole binaries will provide opportunities to test these tenets of GR by examining the multipole structures of black holes.
• Constraining Scalar-Tensor Theories: Systems with distinct gravitational bindings will serve as laboratories for testing scalar-tensor theories, which propose modifications to GR by including scalar fields that couple with matter differently from gravity.

Future Prospects and Theoretical Implications

The paper emphasizes the essential role pulsar observations will continue to play in gravitational physics and expresses the expectation that the SKA will push existing tests to unprecedented levels of precision while enabling entirely novel experiments. These advancements will offer stringent tests of GR and alternative theories, potentially revealing new insights or falsifying existing models, hence driving the development of a unified theory incorporating both gravitational and quantum phenomena.

In conclusion, the research underscores the transformative impact that the SKA will have on pulsar astronomy and experimental gravity, fostering an era of enhanced precision in the paper of the universe's fundamental forces. The SKA will thus not only consolidate the validity of GR but also sharpen the tools with which physicists might explore new theories that address its limitations and integrate it with quantum mechanics.