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arxiv: 2607.02064 · v1 · pith:JEFIEZN7new · submitted 2026-07-02 · 🌌 astro-ph.HE · gr-qc

Testing Gravity with Binary Pulsars in the SKA Era

V. Venkatraman Krishnan , L. Shao , V. Balakrishnan , A. Carleo , M. Colom i Bernadich , A. Corongiu , A. Deller , P. C. C. Freire
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M. Geyer E. Hackmann H. Hu Z. Hu M. Kramer J. Kunz K. Liu M. E. Lower X. Miao D. Perrodin D. S. Pillay A. Possenti S. Ransom I. Stairs B. Stappers The SKA Pulsar Science Working Group
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Pith reviewed 2026-07-03 07:50 UTC · model grok-4.3

classification 🌌 astro-ph.HE gr-qc
keywords binary pulsarsgeneral relativity testsSquare Kilometre Arraystrong-field gravitycosmic censorshipno-hair theorempulsar timinggravitational radiation
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The pith

The Square Kilometre Array will enable deeper tests of general relativity by improving timing of known binary pulsars and discovering dozens of new relativistic systems.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

This paper sets out how the Square Kilometre Array telescope can advance tests of gravity in the strong-field regime through observations of binary and trinary radio pulsars. Higher timing precision on recycled pulsars will permit tighter searches for any departures from general relativity in systems already known. A full Galactic census is expected to turn up many additional relativistic binaries, among them possible pulsar-black hole pairs that could check the cosmic censorship hypothesis and the no-hair theorem. The same data would also address the strong equivalence principle, gravitational dipole radiation, extra field components, gravitomagnetism, and spacetime symmetries. These measurements would supply constraints on gravity that are difficult to obtain by other routes.

Core claim

Binary and trinary radio pulsars act as natural laboratories for strong-field gravity. The SKA's high sensitivity in the Southern Hemisphere will improve timing precision of recycled pulsars, allowing deeper searches for deviations from general relativity in existing systems. A Galactic census will additionally discover dozens of new relativistic pulsar systems, including candidate pulsar-black hole binaries usable for tests of the cosmic censorship hypothesis and the no-hair theorem. The aspects of gravitation to be explored include the strong equivalence principle, gravitational dipole radiation, extra field components, gravitomagnetism, and spacetime symmetries.

What carries the argument

Timing precision of recycled pulsars in binary systems, which supplies the observable used to search for departures from general relativity.

If this is right

  • Deeper searches for deviations from general relativity become possible in already-known binary pulsar systems.
  • Dozens of new relativistic pulsar systems will be found, including candidates for pulsar-black hole binaries.
  • Tests of the cosmic censorship hypothesis and the no-hair theorem can be performed with any pulsar-black hole systems discovered.
  • Measurements of the strong equivalence principle, gravitational dipole radiation, extra field components, gravitomagnetism, and spacetime symmetries will be sharpened.
  • Radiative properties of gravity can be probed with higher precision than before.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Success would give independent checks on strong-field gravity that complement gravitational-wave detections of black-hole mergers.
  • The same timing data could be re-used to place limits on the population of compact objects and on the Galactic supernova rate.
  • If no deviations appear, the results would tighten the parameter space available to alternative gravity theories that predict dipole radiation or violations of the equivalence principle.
  • Non-detection of pulsar-black hole systems at the expected rate would require revision of current models of binary evolution.

Load-bearing premise

The Square Kilometre Array will reach the sensitivity needed in the Southern Hemisphere and the Galactic census will find the expected number of suitable new relativistic systems.

What would settle it

SKA observations that fail to reach the required timing precision on recycled pulsars or that discover far fewer than dozens of new relativistic binaries.

Figures

Figures reproduced from arXiv: 2607.02064 by A. Carleo, A. Corongiu, A. Deller, A. Possenti, B. Stappers, D. Perrodin, D. S. Pillay, E. Hackmann, H. Hu, I. Stairs, J. Kunz, K. Liu, L. Shao, M. Colom i Bernadich, M. E. Lower, M. Geyer, M. Kramer, P. C. C. Freire, S. Ransom, The SKA Pulsar Science Working Group, V. Balakrishnan, V. Venkatraman Krishnan, X. Miao, Z. Hu.

Figure 1
Figure 1. Figure 1: The mass-mass diagram of the Hulse-Taylor pulsar, PSR B1913+16 based on the PK parameters measured by Weisberg & Huang (2016). In the figure the underlying gravitational theory is assumed to be GR. Under this theory, we can calculate bands denot￾ing the 1 − 𝜎 uncertainties in the component masses inferred from various relativistic effects. The fact that all bands meet at the same region in the diagram im￾p… view at source ↗
Figure 2
Figure 2. Figure 2: Comparison of different gravity experi￾ments in terms of spacetime curvature probed and maximum spacetime curvature possible. The y-axis gives the maximum spacetime curvature in the sys￾tem. Since the Y axis is the maximum value of the X￾axis, the lower diagonal is greyed out as impossible. The curvature is calculated as the square-root of the Kretschmann scalar 𝑅𝛼𝛽𝛾 𝛿𝑅 𝛼𝛽𝛾 𝛿 (full contraction of the Riema… view at source ↗
Figure 3
Figure 3. Figure 3: The mass-mass diagram of PSR J0737−3039A/B, also known as the double pulsar (Kramer et al., 2021). In the figure the under￾lying gravitational theory is assumed to be GR. The inset is an expanded view of the region of principal interest, where the intersection of all curves within a small region within measurement uncertainties means that GR has passed all these tests. For more details, see Kramer et al. (… view at source ↗
Figure 4
Figure 4. Figure 4: Fractional error of PK parameters for J0737−3039A with simulated future data. The solid lines represent results using AA* and the dash-dotted lines represent results using AA4. This is perhaps best seen in the double pulsar, where adding just 5-years of MeerKAT data to a 16-year historic dataset, we can already mea￾sure the Shapiro delay with 3× the significance, including higher order contributions to the… view at source ↗
Figure 5
Figure 5. Figure 5: Required number of circular orbit templates as a function of minimum spin period of the pulsar for a SKA-mid survey for DNS and PSRBH systems de￾noted as red and gray lines respectively. The dotted and solid lines assume that there is 33.3% and 50% of the orbit within the observation respectively. The presently envisioned pulsar search pipeline for the SKA’s Galactic plane surveys (assum￾ing the envisioned… view at source ↗
Figure 6
Figure 6. Figure 6: Wall clock pulsar search run time as a function of num￾ber of A100 GPUs for circular orbit searches for DNS and PSRBH binaries. The colors and line styles are same as 5. Keplerian bank searches generally take orders of magnitude longer com￾pared to traditional searches, which is partly why they were never widely adopted in historic surveys. How￾ever, the rapid growth in computing, especially using graphics… view at source ↗
Figure 7
Figure 7. Figure 7: Evolution of the relative error for the derivative of the orbital period as obtained by simulations over ten years of evolved versions of PSR J0737−3039A (with 𝑃b ' 1 hour) and PSR J0514−4002E (with 𝑃b ' 7 hours), assuming the SKA AA∗ and SKA AA4 configurations. We also plot the evolution of the 𝑃¤ b measurement assuming the current orbital configurations for comparison. The observing cadence emulates that… view at source ↗
Figure 8
Figure 8. Figure 8: Present and potential future constraints on Damour-Esposito Farésé (DEF) gravity from binary pulsars for the theory’s linear (𝛼0) and quadratic (𝛽0) coupling coefficients of the scalar field. When 𝛼0 = 𝛽0 = 0, then the theory reduces to General Relativity. The solid red line is the constraints from the 16-year dataset of Kramer et al. (2021). The dash-dotted red line is the double pulsar, if it were discov… view at source ↗
Figure 9
Figure 9. Figure 9: Fractional error of the BH spin measure￾ment as a function of orbital period of a PSR-SBH system. Here we assumed timing observations with weekly cadence and 10-yr time span. For NP, we used 100 𝜇s timing precision from each observation. For MSP, we assumed AA4 sensitivity, and 1-hr observa￾tions per epoch. One of the main aims for SKA pulsar sur￾veys is to discover a PSRBH system. In the Galactic plane, a… view at source ↗
read the original abstract

Binary (and trinary) radio pulsars are natural laboratories in space for understanding gravity in the strong field regime, with many unique and precise tests carried out so far, including the most precise tests of the strong equivalence principle and of the radiative properties of gravity. The Square Kilometre Array (SKA) telescope, with its high sensitivity in the Southern Hemisphere, will vastly improve the timing precision of recycled pulsars, allowing for a deeper search of potential deviations from general relativity (GR) in currently known systems. A Galactic census of pulsars will, in addition, will yield the discovery of dozens of relativistic pulsar systems, including potentially pulsar -- black hole binaries, which can be used to test the cosmic censorship hypothesis and the ``no-hair'' theorem. Aspects of gravitation to be explored include tests of strong equivalence principles, gravitational dipole radiation, extra field components of gravitation, gravitomagnetism, and spacetime symmetries. In this chapter, we describe the kinds of gravity tests possible with binary pulsar and outline the features and abilities that SKA must possess to best contribute to this science.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

1 major / 1 minor

Summary. The manuscript is a forward-looking science-case review for gravity tests with binary and trinary radio pulsars using the Square Kilometre Array (SKA). It claims that SKA's high sensitivity in the Southern Hemisphere will improve timing precision of recycled pulsars for deeper searches of deviations from general relativity in known systems, while a Galactic census will discover dozens of new relativistic systems (including potential pulsar-black hole binaries) usable for tests of the cosmic censorship hypothesis and no-hair theorem. The text outlines specific aspects of gravitation to be probed (strong equivalence principle, gravitational dipole radiation, extra field components, gravitomagnetism, spacetime symmetries) and the SKA capabilities required.

Significance. If the projected timing improvements and discovery yields are realized, the work usefully maps out a set of strong-field gravity tests that are complementary to other experiments and that exploit the unique properties of pulsar timing. It provides a clear roadmap of the observational requirements on SKA. The absence of quantitative error budgets or discovery-rate calculations, however, leaves the central 'dozens of systems' projection unsupported.

major comments (1)
  1. [Abstract] Abstract: the assertion that a Galactic census 'will yield the discovery of dozens of relativistic pulsar systems, including potentially pulsar-black hole binaries' for testing cosmic censorship and the no-hair theorem is presented without any supporting calculation, reference to expected yields, sensitivity thresholds, or error budget. This projection is load-bearing for the claim that SKA will open qualitatively new tests.
minor comments (1)
  1. [Abstract] Abstract: repeated 'will' in the sentence 'A Galactic census of pulsars will, in addition, will yield'.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the positive assessment of the manuscript's significance and for the constructive comment on the abstract. We address the point below and have made revisions to strengthen the supporting references.

read point-by-point responses

  1. Referee: [Abstract] Abstract: the assertion that a Galactic census 'will yield the discovery of dozens of relativistic pulsar systems, including potentially pulsar-black hole binaries' for testing cosmic censorship and the no-hair theorem is presented without any supporting calculation, reference to expected yields, sensitivity thresholds, or error budget. This projection is load-bearing for the claim that SKA will open qualitatively new tests.

    Authors: We agree that the abstract would be strengthened by explicit references to the basis for the projected yields. The 'dozens of relativistic pulsar systems' figure is drawn from published population-synthesis and survey-sensitivity studies of SKA pulsar searches (including estimates for relativistic binaries and potential pulsar-black-hole systems). In the revised version we will insert a concise parenthetical reference to these works in the abstract and will add a short clarifying sentence in the main text that points the reader to the relevant discovery-rate calculations. This addresses the load-bearing nature of the claim without requiring new computations within the present review. revision: yes

Circularity Check

0 steps flagged

No significant circularity: forward-looking review without derivations or fitted predictions

full rationale

The paper is a science-case review outlining prospective gravity tests enabled by future SKA pulsar timing. It contains no equations, no fitted parameters, no predictions derived from internal data, and no self-citation chains that reduce the central claims to prior author work by construction. Claims rest on external assumptions about SKA sensitivity and discovery yields rather than any load-bearing derivation that collapses to its own inputs. This matches the default expectation for non-circular papers; the reader's assessment of score 1.0 is consistent with the absence of any of the enumerated circularity patterns.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No mathematical derivations, fitted parameters, or new physical entities are introduced; the document is a review of observational prospects.

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