The heaviest neutron star on record is 2.35 times the mass of the sun
The record breaker owes its massive success to infalling gas from a companion star

So much gas from an orbiting star (illustrated in orange) fell onto this neutron star (white with green and purple beams) that it began to spin fast, becoming a pulsar, and also grew to a record-breaking mass.
Cruz deWilde/NASA Goddard Space Flight Center