First stable helium compound

Helium is one of the most unreactive elements in the whole periodic table, and is commonly taught as having no stable compounds. However, a truly global collaboration of scientists published a paper in the journal Nature, showing that the compound Na2He could be formed under extreme pressures of 1.1 million times Earth's atmospheric pressure. The helium and sodium do not form traditional ionic nor covalent bonds, but do start to share electrons in a crystalline lattice. The compound produced is highly insulating and was only formed by using a diamond anvil to create the enormous pressures involved.