Astronomy Practice Exam

How does a barred spiral galaxy differ from a regular spiral galaxy?

1. It has a higher density of stars

2. The spiral arms originate from a central bar of material

3. It is mostly composed of dark matter

4. It has less luminous stars than other galaxies

The correct answer is: The spiral arms originate from a central bar of material

A barred spiral galaxy is characterized by its distinctive structure, where the spiral arms are seen to originate from a central elongated bar of stars and other material that spans the core of the galaxy. This bar structure is a key feature that differentiates barred spiral galaxies from regular spiral galaxies, where the arms emerge more directly from the central bulge without the intermediary bar formation. The formation of this bar is believed to be linked to the dynamics of the galaxy, where gravitational interactions can lead to the elongation of the core. Consequently, the spiral arms in a barred spiral galaxy form from the ends of the bar, making this morphology distinct and visually recognizable. While the other answer choices might pertain to certain aspects of galaxies in general, they do not specifically define what makes a barred spiral galaxy unique. For example, the density of stars, composition regarding dark matter, or luminosity levels can vary between different galaxies irrespective of their spiral classification. Hence, the presence of the central bar and its relationship with the spiral arms stands out as the primary distinguishing feature of barred spiral galaxies.