Barred spiral galaxies are captivating celestial formations that add a unique twist to the classic spiral galaxy structure. These galaxies possess a central bar-shaped structure made up of stars, a distinctive feature that distinguishes them from traditional spiral galaxies. Bars are a common phenomenon in the universe, gracing approximately two-thirds of all spiral galaxies.
The Milky Way Galaxy, home to our Solar System, is itself classified as a barred spiral galaxy within the realm of cosmic formations. This classification, attributed by renowned astronomer Edwin Hubble, provides insight into the diverse nature of galaxies and their intricate designs.
Edwin Hubble’s classification system assigns the label “SB” (spiral, barred) to this galaxy type. The various sub-categories are differentiated by the openness of their spiral arms. SBa galaxies showcase tightly bound arms, while SBc types possess loosely bound arms. The intermediate category, SBb, falls between these two extremes. There’s even a designation, SB0, for barred lenticular galaxies. A relatively newer classification, SBm, has emerged to accommodate irregular barred spirals such as the Magellanic Clouds.
The creation of a bar structure in a spiral galaxy is linked to the propagation of a density wave from the galaxy’s core. This wave influences the orbits of stars, gradually giving rise to a bar-shaped structure. Over time, this effect extends to stars farther out, resulting in the self-perpetuating bar formation. The bar itself serves as a nurturing ground for star formation, channeling gas from the spiral arms towards the center of the galaxy. This process contributes to the presence of active galactic nuclei observed in many barred spiral galaxies.
While bars play a significant role in galaxy evolution, they are not a permanent fixture. These structures eventually decay, leading to a transformation from a barred spiral into a more conventional spiral pattern. The stability of the bar structure is compromised when its mass accumulates beyond a certain threshold. Thus, galaxies with higher central mass tend to exhibit shorter and stubbier bars. This cyclical transformation is estimated to take around two billion years on average.
Recent studies indicate that the presence of bars in spiral galaxies is an indicator of their maturity. Over time, as galaxies evolve, the percentage of spiral galaxies with bars increases. Notably, around 65 percent of modern local spiral galaxies possess bars, a significant rise from the 20 percent observed in distant galactic counterparts.
In the grand cosmic dance, barred spiral galaxies offer a mesmerizing glimpse into the intricate interplay of celestial forces. Their ever-changing nature and influence on star formation add depth to our understanding of the cosmos, reminding us of the dynamic and captivating universe that surrounds us.