Barred Spiral Galaxies

Galaxies can also exhibit elongated features of stars in their central regions, known as bars. These are present in about half of the spiral galaxies in the nearby universe and have an important role in the evolution of their host galaxy. For example, they can drive gas toward the central regions of galaxies, fuelling their central supermassive black hole. Bars form when a disk of stars becomes massive enough to trigger a gravitational instability that re-arranges them into these elongated structures. Tidal interactions with nearby galaxies can also contribute to the formation of bars.

For more cool facts about spiral galaxies, click this link!