Dark matter and the first stars: a new phase of stellar evolution (0705.0521v2)

Abstract: A mechanism is identified whereby dark matter (DM) in protostellar halos dramatically alters the current theoretical framework for the formation of the first stars. Heat from neutralino DM annihilation is shown to overwhelm any cooling mechanism, consequently impeding the star formation process and possibly leading to a new stellar phase. A "dark star'' may result: a giant ($\gtrsim 1$ AU) hydrogen-helium star powered by DM annihilation instead of nuclear fusion. Observational consequences are discussed.

• The paper demonstrates that dark matter annihilation can generate sufficient heat to disrupt traditional cooling, suggesting the emergence of a dark star phase.
• It employs adiabatic contraction models with parameters like ⟨σv⟩ = 3×10⁻²⁶ cm³/sec and a 100 GeV particle mass to detail dark matter density evolution.
• Implications include a redefined view of primordial star formation and reionization, prompting calls for enhanced simulations to resolve DM effects in early cosmic evolution.

Dark Matter and the Formation of the First Stars: A New Phase of Stellar Evolution

The research outlined in the paper, "Dark matter and the first stars: a new phase of stellar evolution," provides a substantial reevaluation of star formation theories pertaining to the primordial stars of the universe. The paper identifies a mechanism wherein dark matter (DM) annihilation significantly impacts the theoretical framework governing the formation and evolution of the first stars, proposing the possible existence of a unique stellar phase, termed as "dark stars," powered by DM annihilation rather than conventional nuclear fusion processes.

Key Findings

The paper elucidates that dark matter, particularly the annihilation of neutralinos—considered a viable DM candidate within supersymmetric models—can produce substantial heat that affects the cooling processes necessary for star formation. Predominantly composed of DM (85%) along with pristine hydrogen and helium from Big Bang nucleosynthesis (15%), these protostellar halos are thought to be the sites of the universe's first stars, typically formed in DM haloes with mass ranging from $10^5$ to $10^6 M_\odot$ at redshifts $z=10-50$.

The research explores how the heat generated through WIMP (Weakly Interacting Massive Particles) annihilation can surpass the molecular hydrogen cooling mechanisms. Employing parameters such as $$\langle \sigma v \rangle = 3 \times 10^{-26} {\rm cm^3/sec}$$ and $m_\chi = 100$ GeV for the SUSY particle mass, the paper explores the annihilation processes within these dense regions.

The paper employs adiabatic contraction to estimate DM density profiles, characterizing the DM's response to the increasing gravitational potential of collapsing baryons. The anticipated DM density at the halo's outer edge scales with baryon density according to $$\rho_\chi \simeq 5 {\rm GeV/cm}^{-3} (n/{\rm cm}^{3})^{0.81}$$. It reveals that as baryon density within these protostellar cores increases, DM heating induced by annihilation competes with, and often overtakes, established cooling mechanisms.

Implications and Future Directions

The research proposes the presence of "dark stars," potentially achieving equilibrium powered by DM annihilation—a transformative concept in stellar evolution models. These dark stars could provide insights into the reionization history of the universe, potentially offering explanations for discrepancies in measurements like $\sigma_8$.

Moreover, the paper speculates on the potential longevity of these dark stars, posing questions about whether they still exist today, or whether they represent an intermediate phase leading to standard stellar formation. The implications on the initial mass function for Pop III stars are significant, suggesting that DM heating could alter the mass and luminosity of these stars, impacting both reionization and heavy element formation necessary for subsequent stellar generations.

The paper recognizes the necessity for enhanced simulations to improve DM resolution in the context of Pop III star formation. Such advancements could validate or refine the theories posited.

Observational Consequences

While observational confirmation of the dark star phenomenon remains challenging due to the limitations of current neutrino and gamma-ray detectors, upcoming missions like the James Webb Space Telescope may aid in distinguishing these entities at $z\sim 10$ through their unique spectral characteristics. The paper also speculates that remnants of these dark star phases might still be detectable as distinct sources based on enhanced DM annihilation patterns within relic halos.

The paper stimulates further exploration into the interface between astrophysics and particle physics, inviting researchers to explore the nuances of DM effects on cosmic evolution. The authors provide a compelling impetus for considering DM interplay in early universe models, urging reconsideration of established paradigms in stellar astronomy and opening avenues for novel lines of inquiry in the cosmological sciences.