A galactic bulge is a centrally concentrated stellar population in a galaxy, usually thicker than its disk. Its origin, rotation and random stellar motions can differ from those of the disk; bulge light is often described by a Sérsic profile.
A pseudobulge is a central stellar concentration in a disk galaxy whose structure and dynamics indicate growth through internal disk evolution rather than only rapid merger-driven assembly. A central brightness excess alone does not establish this origin.
Disk-like flattening, appreciable ordered rotation, nuclear spiral arms, galactic bars and ongoing star formation provide complementary diagnostics. A bar can torque gas and move it inward, feeding central star formation over a long timescale. Individual diagnostics are imperfect, so classifications combine imaging and kinematics instead of equating every low-index brightness profile with a unique history.[ref]
Secular Evolution and the Formation of Pseudobulges in Disk Galaxies by John Kormendy and Robert C. Kennicutt Jr.. Abstract, disk-like diagnostics and bar-driven gas redistribution
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The galactic bulge is the dense, central region of a galaxy, particularly prominent in spiral galaxies. It is characterized by a concentration of stars, gas, and dust, often forming a rounded or spheroidal shape. The bulge typically contains older stars, as well as a higher density of stars compared to the surrounding disk of the galaxy.