The loops are examined as radio and soft X-ray sources under the assumption that they are objects related to the Gum Nebula but much older than it. The loop diameters are likely on the scale of 100 pc or more, as reported recently. This is naturally understood with the fossil Stromgen sphere model. Further progress in understanding the origin of the loops depends on the resolution of certain observational issues.
Kafatos, M., Morrison, P. (1973) Giant Loops as Fossil Stromgren Spheres: Their Radio and X-Ray Emission, Astronomy and Astrophysics Vol. 26: 71-77. Retrieved from http://adsabs.harvard.edu/full/1973A%26A....26...71K