There are three prominent galaxies in this picture: NGC 4725 the one-armed supergiant, NGC 4747 the neighbour of the giant, and NGC 4712 which is five times farther then the other two.
One armed peculiar galaxy: NGC 4725
NGC 4725, the largest galaxy in the picture, is a barred spiral galaxy about 40 million light years away from Earth in the direction of constellation Coma Berenices. It has active galactic nucleus, which means the luminosity of the core is much higher than normal. This phenomenon is most probably caused by an accretion disk around a supermassive black hole located at the center of the galaxy. NGC 4725 is classified as type 2 Seyfert galaxy, because the spectrum of the core shows emission lines from highly ionized gas. The matter falling in the accretion disk is getting compressed and so hot that it radiates at UV and X-ray wavelengths. This radiation is responsible for the ionization of the gas.
Around the core two bars were identified, rotating independently from each other. They are thought to be involved in feeding the active nucleus with gas. The core region is surrounded by a well defined ring structure glowing in blue. The blue light is coming from very young stars, the evidence of an intense star formation happened in the ring recently. Opposed to the blue colour of the ring, the core region of the galaxy and the bars shine in yellow, revealing they contain much older stars.
While most spiral galaxies have two or more spiral arms, peculiar galaxy NGC 4725 has only one arm emerging from the ring surrounding the central region of the galaxy. The barred core, the ring and the only one arm result NGC 4725 to be classified as SAB(r)ab pec according to De Vaucouleurs system.
NGC 4747
The other prominent galaxy in the lower part of the picture is NGC 4747. It is about 45 million light years away from us, slightly farther than NGC 4725. It is an edge-on spiral galaxy with thick dust lanes, and several tidal loops.
The direction of the tails of NGC 4747 can be traced back directly to the supergiant galaxy NGC 4725, making it very probable that these two galaxies are gravitationally interacting with each other. This interaction can also be the cause why NGC 4725 has only one arm.
NGC 4747 has a yellow colured core consisting of older stars, and blue spiral arms similar to its giant neighbour.
There is also a very distant cluster of galaxies visible in the bottom center part of the image. Their distance is about 2 billion light-years. Those galaxies are moving away from us at very high speed, causing their light to be shifted towards the red wavelengths.
NGC 4712
NGC 4712 is a more distant spiral galaxy compared to NGC 4725 and NGC 4747. Its distance is approximately 200 million light years from the Earth, about five times farther than the other two, but only at 1/10th of the distance of the galaxy group seen in the image of NGC 4747.
Despite its huge distance, the structure of the galaxy can be clearly seen in the picture. Yellow central region with dust lanes, and blue scattered spiral arms.
The distribution of old and young stars in this galaxy is the same as in the other two: old stars at the center, young stars in the outer regions.
