Glossaire - N

Nebula refers to a region of indistinct nebulosity. In modern terms, it means an interstellar cloud of dust, hydrogen, helium and other ionized gases. Historically, it was also used to refer to extended sources of luminosity that could not be resolved into their individual components, such as star clusters and galaxies.

Neutron star is a type of stellar remnant that is composed almost entirely of neutrons, which is a type of subatomic particle with no electrical charge. Typically, a neutron star has a mass between 1.35 and about 2.0 times the mass of the Sun, but with a radius of only 12 km (7.5 mi).

Number density is the quantity of some specified particle or object class per unit volume. For atoms, molecules or subatomic particles, the volume is typically in cm−3 or m−3. With stars, cubic parsecs (pc−3) are often used.