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Formation and stellar evolution in ultra-dense stellar systems implied by star-dominated interpretations

Investigate viable formation pathways for ultra-dense stellar systems with extreme central densities implied by star-dominated models of The Cliff, and characterize how stellar evolution proceeds in environments with frequent high-velocity envelope-piercing collisions, including their dynamical, radiative, and X-ray signatures.

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Background

If the rest-optical continuum of The Cliff is attributed to a massive, ultra-compact stellar population, the implied densities lead to frequent high-velocity stellar collisions and unusual dynamical conditions.

The authors note fundamental unknowns regarding how such systems could form from the interstellar medium and how stars evolve under frequent envelope-piercing collisions, underscoring the need for theoretical and numerical studies.

References

Of course, these considerations leave open a number of fundamental issues in considering such ultra-dense systems. Foremost, how could such systems ever have formed from an ISM? Or, how does stellar evolution proceed in an environment of frequent stellar envelope piercing?

— A remarkable Ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a Little Red Dot at $z=3.5$ (2503.16600 - Graaff et al., 20 Mar 2025) in Section 5.2 (Kinematics of ultra-dense stellar systems)