NASA has released a beautiful photo taken by the NASA/ESA Hubble Space Telescope of the galaxy group Arp-Madore 2339-661, so named because they belong to the Arp-Madore catalogue of peculiar galaxies. However, the particular peculiarity might be even odder than first meets the eye, as there are in fact three galaxies interacting here, not just two.
This Hubble image shows Arp-Madore 2339-661, a group of three interacting galaxies some 500 million light-years away in the constellation of Tucana. The color image was made from separate exposures taken in the visible and infrared regions of the spectrum with Hubble’s Advanced Camera for Surveys (ACS) and the Dark Energy Camera (DECam) on the Víctor M. Blanco 4-m telescope at Cerro Tololo Inter-American Observatory. Four filters were used to sample various wavelengths. The color results from assigning different hues to each monochromatic image associated with an individual filter. Image credit: NASA / ESA / Hubble / J. Dalcanton, Dark Energy Survey / DOE / FNAL / NOIRLab / NSF / AURA / L. Shatz.
Arp-Madore 2339-661 resides 500 million light-years away in the constellation of Tucana.
Also known as the NGC 7733-34 group, it consists of three interacting galaxies: NGC 7733, NGC 7734, and NGC 7733N.
NGC 7733 and NGC 7734 are classified as barred spiral galaxies and NGC 7733N as a dwarf galaxy.
NGC 7733 shows knots in the arms and hosts a Seyfert 2 nucleus, while NGC 7734 has peculiar arms.
The latter is at a distance of 157,500 light-years and has a velocity of 406 km per second with respect to NGC 7733.
“The two clearly defined galaxies are NGC 7733 (smaller, lower right) and NGC 7734 (larger, upper left),” Hubble astronomers said.
“The third galaxy is currently referred to as NGC 7733N, and can actually be spotted in this picture if you look carefully at the upper arm of NGC 7733, where there is a visually notable knot-like structure, glowing with a different color to the arm and obscured by dark dust.”
“This could easily pass as part of NGC 7733, but analysis of the velocities (speed, but also considering direction) involved in the galaxy shows that this knot has a considerable additional redshift, meaning that it is very likely its own entity and not part of NGC 7733.”
“This is actually one of the many challenges that observational astronomers face: working out whether an astronomical object really is just one, or one lying in front of another as seen from Earth’s perspective!”
“All three galaxies lie quite close to each other and, as this image shows, they are interacting gravitationally with one another,” they added.
“In fact, some science literature refers to them as a ‘merging group’, meaning that they are on a course to ultimately become a single entity.”
Source : Breaking Science News