Galaxies come in a variety of shapes, and they are categorized accordingly. Elliptical galaxies appear as smooth, featureless blobs of light, while irregular galaxies exhibit bizarre forms due to gravitational interactions with other galaxies. The spiral galaxies, such as our Milky Way, are well-known for their elongated arms that radiate from a central core, creating a remarkable structure.
Recent images captured by the Hubble Space Telescope illustrate the diversity among spiral galaxies. The first image features NGC 3596, which showcases a clean and orderly spiral structure. In contrast, the second image presents galaxy Arp 184 (also referred to as NGC 1961), classified as a peculiar spiral galaxy.
A striking difference between the two galaxies is their appearance from our vantage point on Earth: NGC 3596 is viewed head-on, presenting a uniform shape. Meanwhile, Arp 184 is observed at an angle, revealing its asymmetrical design. This galaxy’s skewed appearance prevents it from fitting perfectly into the spiral classification, leading to its classification as “peculiar” in the whimsical Atlas of Peculiar Galaxies, created by Halton Arp in 1966.
The prominent spiral arm in Arp 184 is broad and noteworthy, yet the opposite side lacks a similarly large arm, highlighting its asymmetry. In contrast, NGC 3596 is characterized by evenly sized spiral arms that glow pink in this image, indicating regions rich in star formation. This raises intriguing questions: why do some galaxies develop spiral arms while others do not, and how do they vary so widely in form? Astronomers are actively exploring these questions, with findings suggesting that the density of stars in specific areas of a galaxy plays a vital role.
According to Hubble scientists, “Spiral arms represent a pattern of varying densities rather than a solid structure. As stars, gas, and dust orbit within a galaxy, they ebb and flow in and out of the spiral arms. Similar to cars navigating a traffic jam, these elements slow down and cluster as they enter a spiral arm before continuing along their galactic journey.”
