Two primary theories explain how the spiral arms of galaxies are maintained: the density wave theory and the self-propagating star formation theory. The density wave theory posits that spiral arms are not made up of material but are instead regions of higher density that rotate around the galaxy, causing stars and gas to cluster and create the appearance of arms. The self-propagating star formation theory suggests that star formation occurs in waves, where the formation of new stars triggers further star formation in adjacent areas, leading to the development of spiral patterns over time. Both theories highlight the dynamic processes that contribute to the structure of spiral galaxies.
The spiral arms
Spiral arms are parts of galaxies - both the galaxies and their spiral arms are huge, by our everyday standards. Spiral arms basically contain most of what the galaxies contain - including stars, dust, gas.
In spiral arms of spiral galaxies
A spiral galaxy or barred spiral.
Spiral arms come in different "flavors": 10% grand-design (two well-defined spiral arms) 60% multiple-arm, 30% flocculent spirals (no well-defined arms at all). Spiral arms seem to be trailing arms, but this is very hard to determine. In some rare cases, spiral arms may lead.
An ordinary spiral galaxy has spiral arms coming out of the core. In a barred galaxy, the central area consists of a bar of stars and the spiral arms are attached to the ends of the bar.
within or on the edges of the spiral arms.
It has no spiral arms.
Arms of spiral galaxies.
A galaxy with arms extending from its center like a pinwheel is typically classified as a spiral galaxy. These arms are regions of higher density where stars, gas, and dust are concentrated, often resulting in active star formation. The spiral structure is maintained by the galaxy's rotation and gravitational interactions, creating a dynamic and visually striking appearance. Prominent examples of spiral galaxies include the Milky Way and the Andromeda Galaxy.
arms
Arms