Details: The Sculptor Galaxy was discovered in 1783 by a female astronomer, Caroline Herschel, who was sister and aunt of the famous father and son astronomers William Herschel and John Herschel, respectively. The galaxy is the fifth brightest galaxy in the sky (excluding the two Megellanic Clouds). It is one of the best galaxies to be observed by a smaller telescope, but is very far south and thereby low on the horizon for most northern observers.

As an intermediate spiral galaxy, the Sculptor Galaxy is between the classifications of a barred spiral galaxy, such as NGC 1097, and an unbarred spiral galaxy such as M51, the Whirlpool Galaxy. The Sculptor Galaxy is roughly the shape of a circular dinner plate, turned on its axis so that we are almost seeing the plate edge on. It is the center and dominate galaxy of the Sculptor Group, a galaxy group of less than 20 galaxies. At only 12.7 million light-years away, it is the closest galaxy group to us. However, the light we observe from this group is older than the human species, since, on average, the light left these galaxies over 12 million years ago! Far off the image to the upper right, a discovered satellite galaxy, NGC 253-dw2, has already passed and disturbed the much larger Sculptor Galaxy. This dwarf satellite galaxy’s fate is likely destined to be swallowed up by the Sculptor on its next pass or two.

Sculptor: The constellation Sculptor, after which the Sculptor Galaxy is named, was too far south to be included in the original list of 48 constellations as recorded by the Greco-Roman astronomer Ptolomy in the 2nd century AD. It wasn’t until 1500 years later that French astronomer Nicolas-Louis de Lacaille introduced 14 new constellations, including Sculptor, during his voyage to the southern hemisphere. He wanted to travel as far south as possible to measure the distances to planets. By using a technique called parallax, he was able to measure the planets positions against the background of stars at the same moment from different parts of the earth. From these measurements he calculated their distances with good accuracy given the timeframe and instrumentation used. Of the 14 new constellations Lacaille named, 13 of them were instruments symbolizing the Age of Enlightenment. Within the constellation Sculptor are other galaxies of interest including the Sculptor Dwarf galaxy , a member of our own Local Group of galaxies, NGC 55, a large irregular galaxy, and the fascinating Cartwheel Galaxy, a lenticular ring galaxy much further away than the Sculptor Group at a whopping 500 million light-years!

Starburst Galaxy: As a starburst galaxy, star formation in the Sculptor Galaxy happens at a much-accelerated pace compared to that of other galaxies. One result of this is the formation of super star clusters which are very massive, recently formed open star clusters. These are thought to be the precursor to globular star clusters such as M15 in our own galaxy that was imaged by the same equipment (camera, telescope, mount) as above. These super star clusters seem to form an ellipse around the Sculptor Galaxy’s core and range from 50 thousand to 14 million solar masses! While star formation is high throughout most of the galaxy, stellar winds of massive stars, as well as deaths by supernovae seem to have reduced the rate of stars formation in the galactic halo visible here as the dark grey area at the edge of the galaxy itself. At the center of the galaxy, called the galactic core, there is little evidence of a defined core like other galaxies, however there is evidence of a supermassive black hole (SMBH) estimated to contain 5 million solar masses, all compressed to an infinitesimally small point!

Annotations. In the image above, hover a mouse or curser over the image to show annotations of the Sculptor Galaxy, with several enlarged insets identifying interesting features! Starting on the far left is an enlarged image of a portion of the galactic halo. Note the very low star formation in this region. Moving counterclockwise, next is the distant spiral galaxy, PGC 198196, likely approaching 100 million light-years away or more. Next is a bit of a puzzling object. It is either a distant ring galaxy as annotated, or it could also be an object on the edge of NGC 253, but that seems unlikely as it does not resemble and cluster or other known nebulae type. Then we see the galactic core including a very high rate of star formation, super star clusters, and a supermassive black hole. Continuing at the top is an enlarged area of reddish emission nebula likely containing stellar nurseries. Next is distant galaxy PGC 198197, followed by another distant galaxy, PGC 782205 with a faint total apparent magnitude of 17.64, making it nearly 50,000 times fainter than the faintest star visible at a dark site on earth!

Below Images: The image below is the same image as above but processed to remove all stars. Since most of the stars in the image our in our own galaxy, this is what the galaxy would appear like outside of our galaxy, if no stars existed along our line of sight. Using a mouse to hover over the image brings all the stars back. Finally, the last image below is a comparison with the current generation of processing to my old generation 2 processing. This is the same data, same set of preprocessed images, but with improved processing techniques. Hovering the mouse over the image fades from the old image to the new processing!

Object Statistics: Constellation: Sculptor, Right Ascension: 0h 47m 33s, Declination: -25° 17' 17”, Apparent Magnitude: 8.0, Size: 27’.5 x 6’.8 (120,000 light-years diameter), Distance 11-12 million light-years.