Cistus, with its many hybrids and cultivars, is commonly encountered as a garden flower. The common name rockrose is applied to the species, a name also shared by the related genera Halimium, Helianthemum and Tuberaria, all in the family Cistaceae. The common name gum cistus is applied to resin-bearing species, especially C. ladanifer.
Quasars are part of a class of objects known as active galactic nuclei (AGN). Other classes include Seyfert galaxies and blazars. All three require supermassive black holes to power them.
in galaxy: Quasars. ...optical object, they found unexpected and at first unexplainable emission lines superimposed on a flat continuum. This object remained a mystery until another similar but optically brighter object, 3C 273, was examined in 1963. Investigators noticed that 3C 273 had a normal spectrum with the same emission lines as observed in radio galaxies, though greatly redshifted (i.e., the spectral lines...