NGC 1851 (also known as Caldwell 73)[9] is a relatively massive[3] globular cluster located in the southern constellation of Columba.

[3] The stellar components show two separate populations of subgiant stars, with the brighter branch being more concentrated in the outer regions of the cluster.

This feature, if combined with the lack of tidal tail or associated stream of stars, suggests the cluster may be a stripped dwarf galaxy nucleus, similar to Omega Centauri, that has been accreted by the Milky Way.

[12] A nearby pulsar PSR J0514−4002E is orbiting a massive object which appears to occupy the "mass gap" between the heaviest neutron stars and the lightest black holes, making it an unusual star system which may be useful for studying theories of gravity.

Two populations of horizontal branch stars have been observed, with the pair having an age difference of around two billion years.