ProtoCentrals

ProtoCentrals are a hypothesized class of compact central structures that form at the cores of proto-galaxies in the early universe. They are envisioned as potential seeds for galactic nuclei, serving as precursors to either supermassive black holes or dense nuclear star clusters, depending on their subsequent growth and feedback processes.

Formation of ProtoCentrals is discussed through several channels. One scenario involves the direct collapse of metal-poor gas in deep gravitational wells, yielding a massive, compact object. Another involves runaway mergers in extremely dense young star clusters, building up a central mass rapidly. In some models, rapid gas inflow and fragmentation also contribute to core buildup. These pathways are not mutually exclusive and may operate under different environmental conditions in the early cosmos.

Typical proposed properties include high central masses, commonly in the range of 10^5 to 10^7 solar masses, and compact sizes of a few parsecs. They are thought to possess deep gravitational potentials and high central densities, enabling efficient accretion or stellar interactions. Their growth is expected to be governed by gas accretion, mergers with other proto-centrals, and feedback from intense star formation or accretion activity.

Evolutionary outcomes depend on the balance between accretion, mergers, and feedback. ProtoCentrals that accrete efficiently may collapse into primordial or rapidly growing supermassive black holes, potentially fueling early quasars. Those dominated by star formation may persist as compact nuclear star clusters, influencing the dynamical and chemical evolution of their host galaxies.

Observationally, ProtoCentrals have no confirmed detections to date and are primarily studied in theoretical models and simulations. Indirect evidence could arise from the demographics of high-redshift galactic nuclei, early quasar populations, or gravitational wave signals from central mergers.

See also: seeds of supermassive black holes, direct collapse black holes, nuclear star clusters, galactic nuclei.