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How do barred spiral galaxies differ from normal spiral galaxies?
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Galaxy
The Whirlpool Galaxy (left), also known as M51, an Sc galaxy accompanied by a small irregular companion galaxy, NGC 5195 (right).
The primary difference between normal spiral galaxies and barred spiral galaxies lies in the structure from which their spiral arms emerge.1
- Normal Spiral Galaxies (S): These galaxies feature spiral arms that emanate directly from the central nucleus.1
- Barred Spiral Galaxies (SB): These galaxies contain a bright, linear feature known as a bar that straddles the nucleus. The spiral arms in these systems unwind from the ends of this bar rather than from the nucleus itself.12
Despite this structural distinction, barred and normal spirals are remarkably similar in other physical characteristics. Their luminosities, dimensions, spectra, and overall distributions are generally indistinguishable. Both classes follow parallel classification sequences—subdivided into types a, b, and c based on the size of the nuclear bulge and how tightly the spiral arms are coiled—and both exhibit the same general color patterns, with blue disks and arms surrounding redder central regions.31