Compact Dark Matter with Globular Cluster Pulsars

Pulsars are exceptionally stable clocks, and a compact dark-matter object passing near the line of sight to a pulsar delays its pulses through the Shapiro effect. The new analysis still awaits peer review, but it already lays out the central claim clearly.

This matters because cosmology operates at the edge of what current instruments can measure, where systematic errors and model assumptions are never trivial. Small discrepancies between independent measurements have historically pointed toward missing physics rather than simple calibration errors, and the ongoing tension in the Hubble constant is a live example of how a persistent disagreement between methods can reshape the theoretical landscape. Each new dataset that approaches this territory with independent systematics adds real information to a problem that has resisted easy resolution for more than a decade. The number of detectable transits is set by the integral over the dark-matter density along the line of sight connecting the Earth and the pulsar. Established pulsars in pulsar timing arrays are typically within one kiloparsec of the Earth and hence sit in a dark-matter density comparable to our local value.

In this work, we explore globular clusters in the inner Galaxy as targets to search for compact dark matter. These high-pulsar-density environments can be cheaply observed with a single telescope beam and enjoy a large dark-matter crossing rate.

Additionally, since the recently detected nanohertz gravitational-wave background is nearly common to the cluster's pulsars, a multi-pulsar analysis can remove much of its. Ranking known clusters, we find that Terzan 5, with 49 pulsars, offers the best reach.

A forty-year campaign of weekly four-hour visits at the sensitivity envisioned for the second phase of the Square Kilometre Array (SKA) would probe compact objects making up $6\%$. Finally, we estimate the foreground from stars and stellar remnants in Terzan 5 and along the sightline.

The relevance goes beyond one dataset because even small shifts in measured parameters can matter when the field is testing the limits of the standard cosmological model. The Lambda-CDM framework describes the observable universe with remarkable economy, but its success rests on two components, dark matter and dark energy, whose physical nature remains entirely unknown. Any credible measurement that tightens or loosens the constraints on those components moves the entire theoretical enterprise forward, regardless of whether the immediate result looks dramatic on its own terms.

It is subdominant near the most sensitive low-mass part of the SKA benchmark, but becomes important over parts of the stellar mass range. Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy.

Because this is still a preprint, the result should be read with genuine interest and proportionate caution. Peer review is not a guarantee of correctness, but it is a process that forces authors to respond to technical criticism from specialists who have no stake in a particular outcome. Preprints that survive that process, often with substantive revisions, emerge with a stronger evidential base than the version that first appeared. Until that stage is complete, the responsible reading keeps uncertainty explicitly visible rather than treating the claims as established findings.

The next step is to see whether the effect survives when independent surveys, different calibration strategies and tighter control of systematic uncertainties enter the picture. Programmes such as Euclid, DESI and the Rubin Observatory will deliver datasets over the next several years that cover the same parameter space with largely independent methods. If the current signal persists through those tests, its theoretical implications will become impossible to set aside. Until peer review and independent follow-up address those open questions, skepticism is not a failure of appreciation for the work; it is part of how science decides what to keep.

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