I have a bit of a fascination with 'Ring' Galaxies and Hoag's Object has to be the best known and prototype example of the genre.
Rather unfortunately, it also happens to be the faintest object I've ever tried to image.
A truly enigmatic object, it was only discovered in the 50's and was originally classified as a planetary nebula, perhaps not surprisingly in view of it's shape. Spectroscopy eventually determined a distance of about 170 Mpa, the inner core diameter of 5kpc and the 'ring' to have inner and outer diameters of 23 and 37 kpc respectively. The object was indeed a Galaxy and a very rare breed of galaxy. Hoag's object has a magnitude of 17.7, a size of 0.8' x 0.8', and a rather faint mean surface brightness of about 17.1 magnitude per square arcmin. The ring is much fainter - maybe as low as 20 mag per sqare arcmin.
The HST has recently produced a magnificent image of this galaxy,
heritage.stsci.edu/2002/21/index.htmlwhich reveals the true glory of the object. By an incredible co-incidence there appears to be another 'ring' galaxy that can be seen beyond Hoag's Object through the gap between the core and the ring.
From what I have read it appears that Hoag's Object is unique in the known universe in that it is the only known 'ring' galaxy to have a perfectly spherical central galaxy.
I can do no better than refer those interested to this excellent account of Hoag's Object for more information.
heritage.stsci.edu/2002/21/lucas ... lucas.html
My image shows a little less detail than the Hubble - in fact I couldn't see it at all on the individual sub exposures. Stacking the 26 x 180 sec exposures produced something but not much. The background is not great due to the extensive contrast stretching needed to reveal anything.
Comments