Image Credit & Copyright: NASA/ESA Hubble Space Telescope.
Time and time again we see pairs of overlapping galaxies and or objects in space that appear to be side by side when they are in fact, not. This odd couple is no different; NGC 5011B (Right) and NGC 5011C (Top center).
Roughly 156 million light years away is NGC 5011B, a spiral galaxy that resides in the Centaurus Cluster of Galaxies which contains well over 100 galaxies and is the nearest supercluster to the Virgo supercluster. NGC 5011C for many years was believed to be alongside its image partner and also a member of the same supercluster. That was however, until they took a closer look.
First and foremost there is no apparent interaction between the two objects. No gravitational imbalance or streams of material being disrupted due to tidal forces. Secondly and most importantly, when they conducted a study on the relative velocity of the two objects they discovered that NGC 5011B (The spiral galaxy) is red shifted at a much faster rate than its neighbor and that rate matches the rate of the Centaurus Cluster. NGC 5011C has a rate of redshift that is similar to the Centaurus A group of Galaxies which lie about 13 million light years away.
With those facts in hand, astronomers could now deduce that at a given size and distance, NGC 5011C contains within it a mass of only about ten million Suns. Thus the object is almost certainly a nearby Dwarf Galaxy comparable to other dwarf galaxies in the local group.
On a personal note, I often do see many objects that appear to be side by side when they are not buy honestly I never found this to be one of them. Albeit I have never seen this pair through a telescope, however the first time I viewed this photo it’s pretty clear that the spiral galaxy is much further away. The dwarf has to be close just due to the fact that dwarf galaxies are much smaller than spiral galaxies and it’s close enough to where the individual stars within it are resolved in the photo. So I’m not sure who this pair fooled or who knows, maybe it did until this photo along with the measurements came into light. Just my 2$.
NAME: NGC 5011B & NGC 5011C.
WHAT IS IT: NGC 5011B Spiral Galaxy / NGC 5011C Dwarf Galaxy.
HOW BIG IS IT?: On the night sky NGC 5011B is about 48” X 24” arcseconds. NGC 5011C is about 1.2’ arcminutes X 48” arcseconds.
HOW FAR AWAY IS IT?: NGC 5011B is approximately 156 million light years away / NGC5011C is approximately 13 million light years distant.
APPARENT MAGNITUDE?: NGC 5011B +14.5 / NGC 5011C +14.2 which makes them both extremely dim, pushing the limits of what an 8 inch telescope can resolve.
WHERE IS IT? (General): Constellation Centaurus.
WHERE IS IT? (Exact RA/DEC): NGC 5011B RA 13h 13m 12s / DEC -43º 15′ 00”. NGC 5011C RA 13h 13m 12s / DEC -43º 16′ 00”.
ESA Hubble page for this photo: http://www.spacetelescope.org/images/potw1253a/
NASA Hubble page for this photo: http://www.nasa.gov/mission_pages/hubble/science/ngc5011b-c.html
ESO page for these objects: http://www.eso.org/public/news/eso0709/
SIMBAD Data page for these objects (NGC 5011B): http://simbad.u-strasbg.fr/simbad/sim-id?Ident=NGC+5011B
DSO Browser page for these objects (NGC 5011B): http://dso-browser.com/dso/info/NGC/5011B
Cornell University post on NGC 5011C: http://arxiv.org/abs/astro-ph/0701280