  In the cold dark matter (CDM) paradigm, bulges easily form through galaxy
mergers, either major or minor, or through clumpy disks in the early universe,
where clumps are driven to the center by dynamical friction. Also
pseudo-bulges, with a more disky morphology and kinematics, can form more
slowly through secular evolution of a bar, where resonant stars are elevated
out of the plane, in a peanut/box shape. As a result, in CDM cosmological
simulations, it is very difficult to find a bulgeless galaxy, while they are
observed very frequently in the local universe. A different picture emerges in
alternative models of the missing mass problem. In MOND (MOdified Newtonian
Dynamics), galaxy mergers are much less frequent, since the absence of dark
matter halos reduces the dynamical friction between two galaxies. Also, while
clumpy galaxies lead to rapid classical bulge formation in CDM, the inefficient
dynamical friction with MOND in the early-universe galaxies prevents the clumps
to coalesce together in the center to form spheroids. This leads to less
frequent and less massive classical bulges. Bars in MOND are more frequent and
stronger, and have a more constant pattern speed, which modifies significantly
the pseudo-bulge morphology. The fraction of pseudo-bulges is expected to be
dominant in MOND.
