This is a Hubble Space Telescope image, showing an irregularly-shaped galaxy, known technically as NGC 4485, which has undergone a dramatic close encounter with a larger companion galaxy, NGC 4490.
Credit: ESA/Hubble & NASA, Acknowledgement: Kathy van Pelt
Although galaxies are vastly spaced, some galaxies that occur in small groups or huge clusters, do interact, strongly affecting each other through the force of gravity, or even collide and merge, ultimately forming a single giant galaxy. These encounters and collisions of galaxies play a major role for the evolution of the cosmos, since they affect the structure and evolution of the interacting galaxies.
Fig. 1 is an image from NASA’s Hubble Space Telescope (HST), showing a beautiful small galaxy, known as NGC 4485. This galaxy belongs to a category of galaxies, known as irregular galaxies, as they do not have distinct regular forms, unlike the spiral or elliptical galaxies. However, NGC 4485 hasn’t always been an irregular galaxy. It was originally a spiral, which has undergone a strong interaction with a larger companion spiral galaxy, NGC 4490.
Due to this close encounter, the two galaxies were distorted, and transformed into irregular galaxies. Also, part of NGC 4485’s material has been pulled towards NGC 4490, forming a trail of bright stars, connecting the two galaxies. This trail is estimated to be about 24,000 light-years long. Now, the most dramatic stage of the encounter between NGC 4485 and
NGC 4490 is over; they have made their closest approach, and are now drifting apart.
Many of the stars in the trail between NGC 4485 and NGC 4490 were born, due to the duo’s interaction. When galaxies approach each other, hydrogen gas, the dominant raw material from which new stars form, is shared between them, triggering an energetic process of star formation, known as a starburst. The orange knots of light in Fig. 1 are starburst regions, gigantic clouds of gas and cosmic dust where new stars form at high rates.
References
NASA
www.nasa.gov/
HST Websites
http://hubblesite.org/
www.spacetelescope.org/