What key structural difference defines a Barred Spiral (SB) classification from a Normal Spiral (S) classification?
Answer
The presence of a distinct bar structure passing through the nucleus.
The primary categorization division between Normal Spirals (S) and Barred Spirals (SB) hinges entirely on the architecture of the central region. Normal Spirals exhibit arms that emerge directly from the central nucleus without any intermediary structure. In contrast, Barred Spirals are defined by possessing a prominent, elongated bar composed of stars that passes through the center. From the ends of this central bar, the spiral arms then sweep outward into the disk. This bar structure has significant dynamic implications, especially regarding the channeling of gas toward the galactic core.
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