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Abell 1185 & Ambartsumian's Knot

Higher resolutions: 3600 x 3600 (100%)

About this Image

Subject Abell 1185 galaxy cluster in Ursa Major.
ObjectsThe brightest members include: NGC 3550, NGC 3561 AKA "The Guitar" AKA Arp 105, NGC 3552, NGC 3554.
Data NED database entries: Abell 1185 Galaxy Cluster, NGC 3561 - "The Guitar".
Description Abell 1185 lies at around 433 million light years from our galaxy, and is moving away from us at a rate of 8700 km/s due to the expansion of the universe. The cluster contains 82 confirmed member galaxies for which common red shifts have been found.

One of the cluster's brightest and most interesting objects is Arp 105 "the Guitar". The main protagonists in this maelstrom of interacting galaxies are the spiral galaxy (NGC 3561B) and the eliptical (NGC 3561A), along with a handful of tidal dwarf galaxies. The debris of their gravitational dance rendering a shape reminiscent of a guitar (see below for a high resolution image crop of this system).

The interacting galaxies are flinging out tidal arcs, sheets and knots of their constituent stars across hundreds of thousands of light years. Some of these will potentially form distinct gravitationally bound condensations of stars and gas in their own right - becoming tidal dwarf galaxies. It seems likely that the independence of these new systems can only be a temporary state of affairs (in this context something potentially lasting millions of years can be considered temporary) given their location in the middle of a cluster.

Halton Arp and the Armenian astronomer Viktor Ambartsumian cite the Guitar as an example of new galaxies being formed as ejections from older galaxies. The tidal dwarf galaxy in question has been given the name "Ambartsumian Knot" - it is the small blue dot off the bottom of the eliptical NGC3561A. It should be noted that although there is general acceptance of the formation of tidal dwarf galaxies, most modern astronomers do not generally agree with Arp and Ambartsumian on the details of galaxy formation including galaxy superfluid's, quasar association, and the like.

Mergers and collisions of the type described above are common within clusters due to the proximity of galaxies to each other. In most clusters you will find, near their heart, dominant massive eliptical galaxies that appear to have grown through accretion of other in-falling galaxies over the eons. Near the centre of Abell 1185 (mid left in the image below) lies NGC 3550, the brightest cluster galaxy (BCG). Look closely at it's center you will see that it contains a rare triple nucleus. From the literature these nuclei have greatly differing velocities and it seems that this is the result of a relatively recent set of mergers that has yet to settle down and the nuclei merge.

Hunting around in the full resolution image above will reveal a plethora of galaxy types and ongoing interactions, and another faint train wreck of a multiple merger.

Image cropsImage crops of the main objects from the above image are shown below.
abell 1185 central region

Crop of the central region of Abell 1185 displayed at 100%.

Ambartsumians Knot

Close up of Arp 105, "the Guitar", displayed at 150%. Ambartsumian's Knot is the small blue object on the right hand side of the base of the guitar.

Technical Details

Date 2010 03 07 - 2010 05 11
Location Pumpkin Patch Observatory, Bourn, Cambridge, UK
Environment ~12C, ~60% humidity, no moon, seeing 3-4 arcs.
Optics Astro Optik 400mm Cassegrain @ prime focus (f=1200mm)
Filters Astrodon LRGB, YR Cyclops filter wheel
Mount Paramount ME
Guiding Borg 101ED/SBIG ST402ME
Camera FLI Microline 16803
Exposure LRGB 290/70/70/60 mins, 10 minute subs
Processing Maxim/DL 5, CCDStack, Photoshop CS
Notes Lum filtered and and RGB filtered images summed for final luminance layer,
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