Sagittarius B2 (Sgr B2) is a massive, dense HII region and molecular cloud complex located near the center of our Galaxy, about 26,000 light-years away. With a mass of some 3 million solar masses and a density of up to 10⁸ particles per cubic centimeter, it is the richest concentration of molecules in the Milky Way Galaxy. Many different types of interstellar molecule have been identified within Sagittarius B2, including glycine, the simplest amino acid (see amino acids, in space) and the sugar molecule glycoaldehyde. Sagittarius B2 may be part of a shell of material ejected by a large explosion.