ARP 147 is one of the interacting galaxy pairs featured in the Atlas of Peculiar Galaxies, compiled by Halton Arp and first published in 1966. This system is particularly notable for its ring-shaped galaxy structure. Located approximately 430 million light-years away in the direction of the Cetus constellation, it represents one of the rare morphological forms resulting from galactic collisions. The system consists of two distinct galaxies, one of which has evolved into a ring structure as a result of the collision.

^{ARP 147 (NASA)}

General Characteristics

ARP 147 was observed in detail by NASA's Hubble Space Telescope in 2008, and its structure was imaged in high resolution. The system exhibits a two-component structure:

• Ring Galaxy: This blue-toned structure consists of young stars and active star-forming regions. It is a typical example of a ring galaxy. The diameter of the ring structure is approximately 30,000 light-years.
• Companion Elliptical Galaxy: This smaller, red-toned galaxy is faint in terms of star formation and is considered the trigger for the formation of the ring structure.

Formation Process and Interaction Mechanism

The ring structure at the center of ARP 147 is thought to have formed as a result of a galactic collision. Such ring-shaped galaxies typically emerge from head-on collisions in which one galaxy passes through the center of another. During this process, the intruding galaxy compresses the interstellar gas of the target galaxy, producing a shock wave that expands outward in the form of a ring. Over time, this ring becomes a density wave that triggers star formation.

These types of collisions generate rings of star formation that expand symmetrically from the center. The blue ring observed in the ARP 147 system hosts a new generation of young stars and regions of hot, ionized gas formed during this process. The ring is expanding outward, and the star formation rate in this region is quite high.

Observational Findings

Images obtained by the Hubble Space Telescope have shown that the inner part of the ring is darker and less dense, while the outer regions are bright and contain hot stars. These observations provide important insights into the distribution of young star populations within the system and its evolutionary processes. In addition, observations in infrared and radio wavelengths have provided detailed data about the structure of the interstellar medium.

Observations published by NASA and ESA in 2008 suggest that the ring structure was formed approximately 40 million years ago as a result of a collision. It was also determined that the system contains large amounts of gas and dust, indicating that star formation is still actively ongoing.

Morphological Classification and Evolutionary Significance

ARP 147 falls into the category of interacting galaxies. This system serves as a case study in the context of post-collision galaxy evolution and ring galaxy formation. Morphologically, ring structures are transitional features that emerge during evolutionary phases. The ring observed in ARP 147 may be the product of a disk galaxy being reshaped irregularly following a collision.

Such systems contribute to the understanding of galaxy evolution, the triggering of star formation, morphological disruption, and structural reformation processes. Additionally, systems like ARP 147 allow researchers to study how star-forming regions are organized under the influence of collisions and the timing of these processes.

ARP 147 is a significant observational example in terms of interacting galaxy dynamics, ring galaxy formation, and star formation processes. The system provides extensive information on the evolutionary effects of galaxy collisions and allows various models regarding the formation of ring-shaped structures and the organization of star formation within them to be tested.