Irregular Galaxy Holmberg II

This image shows dwarf irregular galaxy Holmberg II (also known as Arp 268 and UGC 4305). The galaxy is dominated by huge bubbles of glowing gas, which are sites of ongoing star formation. As high-mass stars form in dense regions of gas and dust they expel strong stellar winds that blow away the surrounding material. The cavities are also blown clear of gas by the shock waves produced in supernovas, the violent explosions that mark the end of the lives of massive stars. Holmberg II is located about 9.8 million light-years away and is found in the constellation Ursa Major (the Great Bear).