In Astrophysics we learned about Sirius A and B. Sirius is the brightest star you can see in the sky (aside from the sun) and is actually two stars in a binary system. Sirius A, the larger of the two and the brighter, and sirius B, the smaller and dimmer of the two. Sirius B, as we calculated in astrophysics actually has a density to the order of 10^9 larger than water! amazing that its surface is much much harder than diamonds! This is because Sirius B is a white dwarf. White Dwarfs are small stars with relatively huge masses, which leads to large densities. They have these densities because the white dwarfs are no longer kept in equilibrium by hydrogen burning, they have burnt up almost all of their hydrogen, they are no longer made of atoms with chemical bonds to each other, rather plasma made of unbound nuclei and electrons, which allows nuclei to get very very close to one another. So though the second star is small, it is very very interesting
