This swirling object in the constellation Coma Berenices is a barred spiral galaxy. Although at first glance it may appear typical of barred spirals, it is actually rather unusual. Like other spirals (see NGC 4156), M91 has a bar—the elongations emerging from the galactic nucleus—that is connected to the spiral arms. The bar and the arms are both home to dark lanes of dust and bright regions of star formation.
    Somewhat more unusual is M91’s incomplete ring structure. In most barred spirals, the arms completely encircle the galaxy—not here. Even stranger is where the arms emerge from the bar. In ordinary spiral galaxies, the arms emerge from the bar’s ends; here, although difficult to see,