NGC 6712

Lore & Background

NGC 6712 was probably first spotted by Le Gentil on July 9, 1749, who described it as a 'true nebula' to distinguish it from the open cluster M11. William Herschel independently discovered it on June 16, 1784, cataloging it as H I.47 and initially classifying it as a round nebula. It was John Herschel who, during his observations in the 1830s, first described it as a globular star cluster.

The cluster appears to be about 12 billion years old and may have originally been significantly more massive, having undergone substantial mass loss due to passes through the galactic disc. For a globular cluster, NGC 6712 is somewhat metal-rich.

NGC 6712 contains a black widow pulsar designated PSR J1853−0842A. This system consists of an extremely rapidly rotating pulsar accompanied by a low-mass star or brown dwarf. The pulsar's intense radiation contributes to the evaporation of its companion, which has a mass between 0.018 and 0.036 solar masses. Although pulsars typically slow down with age, PSR J1853−0842A is accelerating—a phenomenon that would not be possible without its location within a globular cluster.

Reader's Guide

NGC 6712 holds significance as a globular cluster with a well-documented history of discovery and reclassification, from Le Gentil's 'true nebula' to John Herschel's recognition of its true nature as a globular star cluster. Its age of about 12 billion years places it among the older clusters, and its relatively high metallicity for a globular cluster is noteworthy. The cluster's past mass loss from galactic disc passages suggests it was once much more massive.

The most remarkable legacy of NGC 6712 is its black widow pulsar, PSR J1853−0842A. This system demonstrates the extreme physics of pulsar evolution within dense stellar environments. The pulsar's acceleration, contrary to the typical slowdown of aging pulsars, is only possible because of gravitational interactions within the cluster. The companion's low mass and ongoing evaporation by the pulsar's radiation illustrate the dynamic processes that shape such binary systems. This makes NGC 6712 a key object for studying pulsar recycling and the evolution of compact binaries in globular clusters.

Did You Know?

• NGC 6712 was probably discovered by Le Gentil on July 9, 1749.
• John Herschel was the first to describe it as a globular star cluster, in the 1830s.
• It hosts a black widow pulsar, PSR J1853−0842A, which is accelerating.
• The cluster may have originally been significantly more massive before losing mass through galactic disc passes.