D2 P-Pdot Diagram

Topic

Central to this model are the pulsar's rotation period and the slow drift that period undergoes over time.

Plotting a pulsar based on its rotation period and the rate at which that period increases over time categorizes the observed pulsar population into groups defined by age and magnetic field strength; this serves a diagnostic function exactly analogous to the role the luminosity-temperature diagram plays for ordinary stars.

Young pulsars with strong magnetic fields occupy one region of this diagram; evolved pulsars—nearing a "death line" beyond which the emission mechanism itself should cease—occupy a distinct region; and millisecond pulsars—recycled through the accretion of matter from a companion star that spun them back up—form a completely separate population.

Since both magnetic field strength and the pulsar's remaining reservoir of rotational energy can be inferred directly from its position on this diagram, simply timing its rotation period over years allows for the reconstruction of much of its physical history, without ever needing to resolve the object as anything more than a mere point of light. Thus, from the rotation period that opens this document to the reconstructed physical history that concludes it—taking in the three pulsar populations and the death line marking the shutdown of the emission mechanism—pulsar timing transforms the simple ticking of a cosmic clock into a revelation of both the pulsar's age and its ultimate fate.

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