My original plan was to expose multiple nights of this field in order to capture the NGC 4151 external ring properly, but this was not possible due to the bad weather/moon combination. I processed the single (windy) night data anyway, handling the extreme ring faintness as best as I could.
The landscape is interesting, including two opposites: the extremely active NGC 4151 with a suspected binary black hole in the nucleus and X-Ray emission, and the super-quiet NGC 4145, that seems to be kept alive from a weak interaction with the not-so-close neighbor NGC 4151. Not to be overseen the distant NGC 4156, whose double arm structure is clearly recognizable in our picture.
Picture 1: The cute NGC 4156 is in reality a big galaxy 303 million light-year away. Closeup from the main image.
Follows a short description of the objects. Data mostly extracted by Wikipedia, and Simbad DB.
NGC 4151 Seyfert GalaxyNGC 4151 is an intermediate spiral Seyfert galaxy with weak inner ring structure located 52 million light-years from Earth in the constellation Canes Venatici. The galaxy was first mentioned by William Herschel on March 17, 1787; it was one of the six Seyfert galaxies described in the 1943 paper (C. K. Seyfert. "Nuclear Emission in Spiral Nebulae". Astrophysical Journal. 97: 28–40) which defined the term.
It is one of the nearest galaxies to Earth to contain an actively growing supermassive black hole. The black hole would have a mass on the order of 2.5 million to 30 million solar masses. It was speculated that the nucleus may host a binary black hole, with about 40 million and about 10 million solar masses respectively, orbiting with a 15.8-year period. This is, however, still a matter of active debate.
Some astronomers nickname it the "Eye of Sauron" (From Tolkien's "The lord of the rings") due to its appearance.
Today it is confirmed that the nucleus is a sourcce of X-Rays, firts detected in 1970 by the observatory satellite Uhuru and confirmed later by HEAO 1. X-ray emission has been explained by two different models:
1. radiation of material falling onto the central black hole (which was growing much more quickly about 25,000 years ago) was so bright that it stripped electrons away from the atoms in the gas in its path, and then electrons recombined with these ionized atoms
2. the energy released by material flowing into the black hole in an accretion disk created a vigorous outflow of gas from the surface of the disk, which directly heated gas in its path to X-ray emitting temperatures
Picture 2: NGC 4151 NASA Composite Image X-rays (blue), Ha optical data (yellow), radio observation (red).
X-ray: NASA/CXC/CfA/J.Wang et al.; Optical: Isaac Newton Group of Telescopes, La Palma/Jacobus Kapteyn Telescope, Radio: NSF/NRAO/VLA -
http://www.chandra.harvard.edu/photo/2011/n4151/NGC 4145NGC 4145 is a barred spiral galaxy located in the Ursa Major galaxy cluster, 68 million light years from the Earth. The galaxy has little star formation, except on its outer edges. Due to the loss of energy that occurs without star formation, some astronomers predict that the galaxy will degenerate into a lenticular galaxy in the near future. However, the galaxy's interaction with NGC 4151 may "maintain [its] star formation".
PGC 38778Also known NGC 4145A-1 or MCG 7-25-46, it is a spiral galaxy about 54 million light-years from Earth.
NGC 4156NGC 4156 is a barred galaxy with active nucleus. It is 303 million light years away and has a diameter of 115000 light years.
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