20 euro - The Neutron Star

The words ‘crust’ and ‘core’ are marked in German on the coin’s obverse. ‘Crab pulsar’ is the name of a neutron star that was created from a supernova in the year 1054, while ‘1,4 M ’ refers to the neutron star’s solar mass, ‘30rps’ to its rotation speed per second and ‘r~10km’ to its radius. On the coin’s reverse, the neutron star bulges through a coloured imprint and a stylised representation of its magnetic field. As far as the exact composition of neutron stars is concerned, many things are still a mystery to scientists, but it is hoped that new insights will be gained by studying the expansion of the universe.

There are thought to be up to one billion neutron stars in the Milky Way. This figure is obtained by estimating the number of stars that have undergone a supernova explosion, a spectacular explosion of a massive star. Combined with gravitational collapse, this creates a compact and super-dense object known as a neutron star. After black holes, neutron stars are the densest stellar objects in the universe. Even denser than atomic nuclei, which is a good way to think of them, neutron stars are heavier than the Sun itself: a teaspoonful of neutron star would weigh as much as 1,000 Cheops pyramids. Neutron stars can rotate at very high speed – up to 700 revolutions per second – and have a magnetic field 12 to 15 orders of magnitude stronger than that of the Earth, which is a thousand to a million times stronger than the strongest man-made magnetic fields ever produced.