PSR B1620-26 PSR B1620-26 PSR B1620-26 is a binary star system located at a distance of 3,800 parsecs (12,400 light-years) in the globular cluster of Messier 4 (M4, NGC 6121) in the constellation of Scorpius. The system is composed of a pulsar (PSR B1620-26 A) and a white dwarf star (WD B1620-26 or PSR B1620-26 B). As of 2000, the system is also confirmed to have an extrasolar planet orbiting the two stars. The double system ("triple" including the substellar companion) is just outside the core of the globular cluster. The age of the cluster has been estimated to be about 12.2
Unit distance graph graph so that the edges are exactly the unit distance pairs, may greatly differ from each other: the 2"n"-vertex crown graph may be embedded in four dimensions so that all its edges have unit length, but requires at least "n" − 2 dimensions to be embedded so that the edges are the only unit-distance pairs . It is NP-hard, and more specifically complete for the existential theory of the reals, to test whether a given graph is a unit distance graph, or is a strict unit distance graph . It is also NP-complete to determine whether a unit distance graph