In their landmark study of the Virgo Cluster, Binggeli et al. (1987) found that ∼ 25% of the dEs contain a massive star cluster at their centers (called the nucleus), which clearly stands out against the low surface brightness of its host galaxy. Following this study it has become customary to split the population of dEs into ‘nucleated’ and ‘non-nucleated’. Binggeli et al. (1987) did not detect any nuclei in the more luminous ellipticals, although they cautioned that these might have been missed in their photographic survey due to the high surface brightness of the underlying galaxy. Indeed, more recent studies, capitalizing on the high spatial resolution afforded by the HST, have found that as much as ∼ 80% of all early-type galaxies with 
are nucleated ... In addition, HST imaging of late-type galaxies has revealed that 50–70% of these systems also have compact stellar clusters near their photometric centers ... These show a remarkable similarity in luminosity and size to those detected in early-type galaxies. However, the nuclear star clusters in late-type galaxies seem to have younger stellar ages than their counterparts in early-type galaxies Thus a large fraction of all galaxies, independent of their morphology, environment or gas content, contain a nuclear star cluster at their photometric center. The only exception seem to be the brightest ellipticals, with 
which seem to be devoid of nuclear star clusters. Note that this magnitude corresponds to the transition from disky, power-law ellipticals to boxy, core ellipticals , supporting the notion of a fundamental transition at this luminosity scale.
On average, nuclear star clusters are an order of magnitude more luminous than the peak of the globular cluster luminosity function of their host galaxies, have stellar masses in the range ~ 10⁶–10⁸ 
and typical radii of ~ 5 pc. This makes nuclear star clusters the densest stellar systems known . In fact, they are not that dissimilar to the ultra-compact dwarfs, suggesting a possible relation .
... the majority of bright spheroids (ellipticals and bulges) seem to contain a supermassive black hole (SMBH) at their nucleus. The majority
of spheroids with secure SMBH detections have magnitudes in the range 
.
Although it is unclear whether (the majority of) fainter spheroids also harbor SMBHs, current data seems to support a view in which bright galaxies (
) often, and perhaps always, contain SMBHs but not stellar nuclei, while at the faint end (
) stellar nuclei become the dominant feature. Intriguingly, have shown that stellar nuclei and SMBHs obey a common scaling relation between their mass and that of their host galaxy, with 
(where CMO stands for central massive object), suggesting that SMBHs and nuclear clusters share a common origin. This is somewhat clouded, though, by the fact that nuclear star clusters and SMBHs are not mutually exclusive. The two best known cases in which SMBHs and stellar nuclei coexist are M32 and the Milky Way .
