JAKARTA – NASA’s Hubble Space Telescope has clicked on another cosmic miracle: the interaction of two galaxies so closely intertwined that they are collectively marked as one entity.
Galactic interactions are not uncommon. In fact, a large number of galaxies show some form of interaction, whether with their satellites or on a much larger scale with other galaxies. The latter category may include events such as collisions that end in fusion of galaxies or lead to explosions of star formation.
In a collision and eventual fusion scenario, the larger galaxy may retain its shape after eating a much smaller galaxy. Gravitational interactions between galaxies often lead to the formation of larger irregular galaxies, but elliptical galaxies are also known to form.
Some of the best examples of galactic interactions are the Messler group 81 (including the dominant galaxy M81 which interacts with the two smaller galaxies NGC 3034 and NGC 3077) and the Cartwheel group of four spiral systems in a beautiful ringline.
Images made by the Hubble Space Telescope show an entity named Arp 91 that lies more than 100 million light-years from Earth. Arp 91 consists of two spiral systems called NGC 5953 and NGC 5954.
In the image above, NGC 5953 is a lower galaxy with higher brightness and a more intact spiral shape. The oval galaxy at the top is NGC 5954. Interestingly, NASA notes that both galaxies are spiral, but that their shape appears strangely incorrect due to their orientation in space with respect for Earth.
A quick look at the image shows that the oval NGC 5954 directs one of its arms towards NGC 5954 due to the strong gravitational interaction between them. Scientists believe that galaxies form weapons because of their rotation about a central axis and another factor called density waves.
These arms are active places of star formation and usually appear brighter as the stars inhabit the region. Interestingly, a recent study found that one of the arms of the Milky Way was broken.
According to a research paper entitled ‘Photometric Traces and Cinematic Interactions’ published in the Astronomical Society of the Pacific, the two galaxies in the Arp 91 system are separated by a distance of 5.8 kiloparsecs and have prominent star-forming regions. However, based on infrared astronomical satellite (IRAS) data, NGC 5953 has a much higher star formation rate per unit area compared to its interacting neighbor.
Interestingly, NGC 5953 is part of the Seyfert Class II galaxy, which is characterized by its light core known as the active galactic nucleus (AGN) and happens to be one of the brightest sources of electromagnetic radiation in the cosmos. Interestingly, the Hubble Telescope recently created an image of one of the Seyfert galaxies that resembles a giant cosmic eye with a bright center.