This video which appeared two weeks ago greatly surprised me, making me realize how little I know of what is known about these objects.
From textbooks and similar, I understood that when sufficient mass is added to a white dwarf, (theoretically or by accretion in a binary system), electrons are being pressured to occupy quantum states beyond those permissible by the theory of relativity. In such circumstances, the electrons can be forced together with the protons, and the star collapses to form a neutron star. However, neutron stars are much more complicated than that simple description suggests.
A neutron star has a very thin atmosphere, above a crust made of iron. However, immediately below the crust, not everything is neutrons. The “neutron fluid” still contains a proportion of protons and electrons with momentum below the relativistic barrier.
Deeper in, and a new phase forms, called “nuclear pasta”. This is projected to be liquid crystal like rather than fluid, and extremely strong and stiff. It first takes the form of a lattice of small spheres or “gnocchi”, and as its proportion increases it will form rods or “spaghetti”, then sheets called “lasagne”. Further in, and reverse phases form, one of continuous pasts with cylindrical voids filled with nuclear fluid, then one of small spherical droplets of nuclear fluid.
These phases have not been observed as such, but are predicted by sophisticated number crunching. Matthew Caplan, first author of research paper highlighted in Holy macaroni! After months of number-crunching, behold the strongest material in the universe: Nuclear pasta • The Register, says:
“While we can’t make nuclear pasta in a lab on earth, we can study analog systems. Lots of polymers and liquid crystals have phases like nuclear pasta, they just have more serious sounding names!” … “One famous example is biological membranes in living cells. We’ve actually studied how the nuclear pasta lasagne exhibits the same structure and structural defects as the endoplasmic reticulum. Often times in science you can learn things about one system by studying another analog system with similar properties.”
(I am familiar with such structures through work on block copolymers.)
Further in, the pressure would render nuclear structures unsustainable. One way of holding off collapse might be for protons and neutrons to convert to hyperons, of which the first in the family is the Λ0 (lambda-zero) hyperon, consisting of one up, one down, and one strange quark.
Total collapse may further be staved off by quark deconfinement, with conversion to quark matter, see Neutron stars cast light on quark matter | CERN. Such matter, possibly a quark-gluon plasma, has been made briefly in particle accelerators.
One outstanding feature of such matter is that the mass of the quarks is much smaller than that of the nucleons from which it is derived. According to Quantum chromodynamics binding energy — Wikipedia,
Most of the mass of hadrons is actually QCD binding energy, through mass–energy equivalence … that is if assuming that the kinetic energy of the hadron's constituents, moving at near the speed of light, which contributes greatly to the hadron mass, is part of QCD binding energy. For protons, the sum of the rest masses of the three valence quarks (two up quarks and one down quark) is approximately 9.4 MeV/c2, while the proton's total mass is about 938.3 MeV/c2. For neutrons, the sum of the rest masses of the three valence quarks (two down quarks and one up quark) is approximately 11.9 MeV/c2, while the neutron's total mass is about 939.6 MeV/c2. Considering that nearly all of the atom's mass is concentrated in the nucleons, this means that about 99% of the mass of everyday matter (baryonic matter) is, in fact, chromodynamic binding energy.
Neutrons would break down into one up quark and two down quarks, and with the constraints imposed under the Pauli exclusion principle, room could be made if half of those down quarks could be converted into strange quarks. One hears about “quark stars” and “strange stars”, but they are different concepts even though they may refer to the same objects.
In connection with quark stars, it mentions 3C58 which is a pulsar (designation PSR J0205+6449) with a nebula, being a supernova remnant somewhat like the Crab Nebula. From its location, it was believed to be the remnant of the 1181 AD supernova recorded by Chinese and Japanese astronomers. The video above suggests that it may be a quark star, or at least have a significant core of quark matter, since it properties fit those of a 5000 year old pulsar, so they suggest it might have cooled more rapidly by neutrino emission.
However, recent work suggests that the Chinese / Japanese supernova remnant may be located in another object, a “zombie star” discovered by Dana Patchick.
This appears to be the result of collision of two white dwarfs, and is referred to as a Wolf-Rayet-like star, since its spectrum is similar to those of the massive very hot stars discovered by two French astronomers, Charles Wolf (1827 – 1918) and Georges Rayet (1839 – 1906). But it is much smaller than those, and may be a supermassive very hot white dwarf which could give rise to a repeat supernova when it runs out of nuclear fuel.
Note: the dim red dwarf Wolf 359 is named for a German astronomer, Max Wolf (1863 – 1932).
Any comments, clarifications, etc., most welcome.