Here's why:

* Formation: Neutron stars are formed when massive stars (about 8-20 times the mass of our Sun) run out of fuel and collapse under their own gravity.

* Extreme Density: The immense pressure during this collapse crushes the atoms, forcing protons and electrons to combine into neutrons. This results in a incredibly dense object – a teaspoon of neutron star matter would weigh billions of tons!

* Similar Density to Atomic Nuclei: The density of a neutron star is comparable to the density of an atomic nucleus. In both cases, matter is squeezed incredibly tightly.

So, while "dead star with the density of an atomic nuclei" accurately describes the situation, the more common and precise term is neutron star.