Page 5, External Galaxies: [Previous Page] [Next Page] [Class Home Page] Text Pages 364 -366

A minority of spirals have an elongated nuclear bulge with spiral arms springing from the ends of the bar. While it is not entirely known how the bar forms (probably through some orbital instability of the central bulge), it is seen in many galaxies.

The classification for a bar in a spiral galaxy is similar to those without the bar, property of the bulge and the extent of the spiral arms. They are designated with a capitol SB.

M65, an SBa galaxy. M65 is a weak example of a barred spiral, SBa. It's bulge almost looks square! This hint of elongation along the bulge is referred to as a bar. Bars can be a bit more difficult to see in early spirals because of their large stellar bulge.

M91, an SBb type galaxy. Bars are challenging to explain, dynamically speaking. It has recently been found that our galaxy, the Milky Way, may have a bar as well! Frequently, the ends of the bar lead into normal spiral arms.

M95, an SBc galaxy. Perhaps the most interesting barred spiral is M95, classified as an SBb galaxy. Beyond having a very prominent bar, the spiral arms coming from the end of the bar seem more like a ring, and in fact, it is referred to as a typical ringed galaxy.