In this beautiful image, captured by the Hubble Space telescope, the dwarf irregular galaxy Holmberg II can be seen, which lies some 10 million light-years away. The galaxy. like many smaller galaxies, is dominated by huge bubbles of glowing gas, which are subject to the formation of many heavy-handed stars. Many of these stars are much more massive than our sun.
These stars typically form in dense regions of gas and dust, which expel huge quantities of stellar winds that erode the stellar materials encompassing them, leaving huge holes that are discernible to us here on Earth. The largest of these cavities spans 5500 light years in width. The cavities are also blown clear of gas by the shock waves produced when any number of stars within the immediate area go supernovae, which happens to all stars that are much more massive than our sun.