Hi Suzy, see this passage to see how the pulsers ect where formed
Discovered by Philippe Loys de Chéseaux (1718-51) in 1746, M4 (NGC 6121) is one of the Milky Way's smallest but closest known globular star clusters. Unfortunately, it is obscured by dark interstellar clouds from the perspective of the Solar System. Located only around 5,600 ly (1,720 parsecs) away in the northwestern part (16:23:35.4-26:31:31.9, J2000) of Constellation Scorpius (lined photo), the Scorpion, it is also one of the most open, or loose, globulars with some 100,000 stars spread over more than 50 ly. As it contains mostly stars around 13 (12.7 +/- 0.35) billion years old (Sigurdsson et al, 2003), most of its higher-mass stars (i.e., Sol-sized and larger) have already evolved out of the main sequence to become white dwarfs, neutron stars, or black holes. (See a photo of some of M4's white dwarfs). Moreover, since most of M4's stars were formed within a billion years of the Big Bang, they are only around five percent as enriched in elements heavier than hydrogen and helium as Sol (Sigurdsson et al, 2003).
I hope this helps
Cheers