Analytic Estimates Show Stellar Collisions Strip Red Giant Envelopes in Galactic Nuclei Producing Helium White Dwarfs at 500 Gyr^{-1}
Analytic modeling of red giant collisions in galactic nuclei shows envelope stripping at high velocities and helium white dwarf production at 500 Gyr^{-1}. The framework explains the inner-arcsecond flattening of the Galactic Center red giant density profile. Limitations include the absence of full hydrodynamics and long-term dynamical evolution.
The 2026 arXiv preprint by Barak Rom applies analytic ram-pressure and shock calculations to red giant encounters with main-sequence stars and stellar-mass black holes in dense nuclear star clusters. It derives velocity-dependent destruction thresholds and estimates the resulting helium-core ejection or envelope removal rates without full hydrodynamical simulations. Applied to the Milky Way center, the models reproduce the observed flattening of red giant projected density inside one arcsecond, attributing the effect to collisions for fainter giants and short evolutionary lifetimes for brighter ones.
These collisions also generate a population of low-mass helium white dwarfs that can undergo tidal disruption events around intermediate-mass black holes of 10^5-6 solar masses, a channel unavailable to carbon-oxygen white dwarfs. The work connects to earlier stellar-dynamical studies of the Galactic Center that reported a deficit of luminous red giants, previously attributed mainly to star formation history or relaxation.
The analytic approach omits detailed binary evolution and cluster relaxation timescales. Three-dimensional hydrodynamical simulations of individual encounters plus N-body integration of the nuclear cluster would tighten the rate predictions and test whether black-hole collisions truly dominate at lower velocities.
Rom: JWST spectroscopy will detect an excess of at least 50 low-mass helium white dwarfs within the inner parsec of Sgr A* by 2035 if the collision rate exceeds 400 Gyr^{-1}.
Sources (2)
- [1]Primary Source(https://arxiv.org/abs/2606.14843)
- [2]Supporting Source(https://arxiv.org/abs/1503.02061)