Neutron Stars have a compaction of 10^17
It has been observed to show properties of a Quark core.
When a core of a star collects enough matter, to form a Neutron Core, the size will develop Dipolar Electromagnetic fields strong enough to expel in the form of an hourglass its solar envelope.
The spin of a Neutron Star, is understood by understanding Chiral Supersymmetry that exhibits Dipolar Electromagnetic Vector fields, expelling matter away, and attracts matter to it.
Neutron Star is not the ashes from a star.
How long will it burn?
Billions of years.
If it's allowed to burn, in time the dipolar magnetic fields lose their power allowing the expelled matter to collect and a solar envelope will form.
If matter is collected than the Neutron matter will break down to quarks, compact to a Quark star and in so doing increase its dipolar vector fields and the vector fields pulling in matter forming a mimic black hole where EMR cannot escape.