Approximately two-thirds of all spiral galaxies contain a bar including our own Milky Way galaxy- but it's bar is barely visible. The current hypothesis is that the bar structure acts as a stellar nursery which actively creates new stars near the center. The thin reddish lines that are visible throughout the galaxy are actually dust lanes where stars are created. Their presence within the bar helps corroborate this opinion. The bar is generally thought to be caused by a wave of higher density that extends from the galaxy's center. At first, the wave changes the orbits of inner stars then, after billions of years, affects stars farther out and, over millions of millennia, elongates as it grows- thus creating this unusual structure.