This month let us explore one of the seminal galaxies in the nigh sky, NGC 253, Caroline Herschel’s galaxy. It shines deep in the southern portion of the sky, south of the bright star Beta Ceti and southeast of the even brighter star Fomalhaut. This is one of my favorite galaxies, largely because of the beautiful story that is associated with its discovery.
Image caption: Measuring 70 000 light-years across and laying 13 million light-years away, the nearly edge-on spiral galaxy NGC 253 is revealed here in an image from the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at the La Silla Observatory. The image is based on data obtained through four different filters (R, V, H-alpha and OIII). North is up and East to the left. The field of view is 30 arcminutes.
This galaxy, which I call Caroline Herschel’s Galaxy, is a starburst galaxy. It is so named because it is undergoing a burst of formation of new stars. This process was set off relatively recently, at lest in cosmic timekeeping. About two hundred million years ago, a smaller dwarf galaxy probably collided with this larger one, and it set off this cacophony of new stars being formed. That other galaxy was probably rich in gas, which provided the raw material for the births of the new stars. There is one thing that this galaxy does not share with other starburst galaxies, however; usually these galaxies exhibit frequent exploding stars or supernovae. This one, however, has only one recorded supernova, in 1940.
This galaxy is aligned at almost right angles to our Milky Way. When you look at it, it appears as a thick pencil-like structure.
While searching for comets during the year 1783, Caroline stumbled across this long, slender galaxy hanging above the southern horizon. Duly recorded in her log “the Bills and Rec.ds of my comets,” she also began and maintained a list or catalogue of the many objects she and her brother William had discovered, including beautiful drawings of most of them. As a young girl Caroline was close to her father, who brought her outdoors on a cold evening some winter constellations like Orion. It is possible that this was one of the special moments during which she began her love of the night sky.
As much as Caroline enjoyed working with her brother William, there were some issues. On one night Caroline fell upon one of the large iron hooks that helped support the telescope on its mount. The accident left a large gush in her thigh. Her brother, not seing his telescope moving, yelled out “Make haste!” to which Caroline cried out, “I am hooked!” William immediately rushed over to help his sister, and she eventually recovered, with lots of rest and ointment.
When William married Mary Pitt in 1788, there was an obvious increase in tension among the Herschels. She continued working with her brother, although the increased “family dynamics” did cause a problem. William very much wanted his sister to continue helping with his observing, and he was successful in arranging a royal stipend for her.
In 1802 the Royal Society published the catalogue that Caroline had kept over many years. However, the publication in Philosophical Transactions of the Royal Society was credited to William, even though it was her catalogue. Over a long period of time, thanks to the work of later astronomers like John Louis Emil Dreyer, the almost 8000 objects now comprise the New General Catalogue.
The woman who discovered the wonderful galaxy in Sculptor certainly enjoyed a remarkable life and career, living until she was almost 98 years old. In the 1980s Caroline’s eight comet discoveries were surpassed by Carolyn Shoemaker, in what was seen at the time as the highlight of Carolyn’s career. However exciting that achievement might have been, it was completely eclipsed by her discovery of Comet Shoemaker-Levy 9 in March of 1993. That comet gave humanity its first lesson in what happens when a comet strikes a planet, and by inference, how comet collisions can lead to the origin of life on a world. As I gaze upon Caroline Herschel’s galaxy on these winter nights, I imagine life forms there looking back, trying as we do, to share our cosmic heritage.