"A neutron star is so dense that one teaspoon of its material would have a mass
over 5.5×10^12 kg (900 times the mass of the Great Pyramid of Giza)
In the enormous gravitational field of a neutron star, that teaspoon of material
would weigh 1.1×10^25 N (about 15 times what the Moon would weigh if it
were placed on the surface of the Earth)
The entire mass of the Earth at neutron star density would fit into a sphere
of 305m [~3 football fields] in diameter."
https://en.wikipedia.org/wiki/Neutron_star#Density_and_pressure
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Neutron star
A neutron star is the collapsed core of a giant star which before collapse had a total mass of between 10 and 29 solar masses.[bet 10-29 mass of the Sun]
Neutron stars are the smallest and densest stars, not counting black holes, hypothetical white holes, "quark stars" and "strange stars".[1]
Neutron stars have a radius on the order of 10 kilometres (6.2 miles) and a mass lower than 2.16[2] solar masses.[3]
They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei.
Once formed, they no longer actively generate heat, and cool over time; however, they may still evolve further through collision or accretion.
Most of the basic models for these objects imply that neutron stars are composed almost entirely of neutrons (subatomic particles with no net electrical charge and with slightly larger mass than protons); the electrons and protons present in normal matter combine to produce neutrons at the conditions in a neutron star.
Neutron stars are partially supported against further collapse by neutron degeneracy pressure, a phenomenon described by the Pauli exclusion principle, just as white dwarfs are supported against collapse by electron degeneracy pressure. ..."
There are thought to be around 100 million neutron stars in the Milky Way, a figure obtained by estimating the number of stars that have undergone supernova explosions.[16]
However, most are old and cold, and neutron stars can only be easily detected in certain instances, such as if they are a pulsar or part of a binary system.
Slow-rotating and non-accreting neutron stars are almost undetectable; however, since the Hubble Space Telescope detection of RX J185635−3754, a few nearby neutron stars that appear to emit only thermal radiation have been detected.
Soft gamma repeaters are conjectured to be a type of neutron star with very strong magnetic fields, known as magnetars, or alternatively, neutron stars with fossil disks around them.[17]
