Hildemar's Knots are an exotic, sapient extraterrestrial lifeforms living on a neutron star in the Orion's Arm universe.
They were first discovered in the neutron star KJEI-54-458945 in the Einstein's Revenge Cluster. They are made of knots of the vortex and charge tubes in the neutronium (super densely packed super fluid material made of neutrons) mantle of the neutron star.
An individual Knot is a few centimeters across and lives on soliton waves and neutrino flows. They are based on nuclear matter processes, acting naturally on the femtosecond timescale and have nuclear matter manipulation abilities.
The Knots apparently have a largely non-material culture, where the basis of interaction is "trade in self, orthodoxy and "authentic noise" according to the communication attempts that have been undertaken by various interstellar institutes. The Knots apparently view the world as an eternal and unchanging structure, where they just "play out its logical unfolding in order to cause their existence." Most attempts to contact them have failed, as they view the outside world as an abstract math problem, not something to interact with.
The Einstein's Revenge Cluster consists of 34 neutron stars, all having undergone timed supernovas. It is unknown whether this was caused by the Knots or an alien species which created the Knots. All the neutron stars have their own different version of the Knots.