Star Formation Processes in Galactic Systems

Star formation in galaxies unfolds as a two‐stage interplay between the assembly of cold, dense molecular clouds and the subsequent collapse of denser regions within them to form stars. In the first stage, diffuse interstellar gas cools and condenses under the combined influence of galactic dynamics, including spiral‐arm compression, shear and tidal forces, and turbulence driven by supernova feedback. Metallicity and dust content regulate the efficiency of cooling and molecule formation, leading to variations in cloud structure from massive spirals to metal‐poor dwarfs. Once molecular clouds form, gravity and local instabilities fragment them into cores whose collapse is modulated by magnetic fields, turbulence and radiation feedback from young stars. The balance of gravitational pull, internal pressure and feedback sets characteristic timescales for cloud lifetimes and star formation efficiency. On kiloparsec scales, empirical scaling relations link gas surface density, dynamical equilibrium pressure and orbital times to the star formation rate surface density, revealing a broadly uniform molecular gas depletion time across diverse environments. Variations in these relations trace quenching processes in transitioning galaxies, radial shifts in efficiency within bulges and discs, and the impact of cosmic environment on galaxy evolution. Understanding these processes is vital for reconstructing the star formation history of the Universe and predicting the build‐up of stellar mass in different galactic systems.

Research from Nature Portfolio

Recent studies have demonstrated the presence of molecular gas in extremely metal‐poor galaxies, revealing that carbon monoxide can be detected at metallicities as low as 7% of solar. This finding confirms that molecular reservoirs persist even in quasi‐primitive environments, providing the raw material for star formation in systems analogous to early‐Universe galaxies. Analyses of archival infrared data show that the CO‐to‐H₂ conversion factor in these metal‐poor systems is orders of magnitude higher than in the Milky Way, underlining the need to adjust molecular gas estimates in low‐metallicity regimes and refining our view of star formation in chemically immature galaxies.

Star Formation Processes in Galactic Systems publication trend

The graph below shows the total number of articles in star formation processes in galactic systems across all publications each year (not limited to Nature Index journals).

Technical terms

Molecular cloud: A cold, dense aggregation of gas and dust where molecules (primarily H₂) form and stars subsequently condense.

Kennicutt–Schmidt relation: An empirical power‐law linking gas surface density to star formation rate surface density across galaxies.

Star formation rate surface density (ΣSFR): The mass of new stars formed per unit area per unit time, typically expressed in M☉ yr⁻¹ kpc⁻².

CO‐to‐H₂ conversion factor (αCO): A coefficient used to convert measured CO emission into molecular hydrogen mass.

Molecular gas depletion time (τdep): The time required for the existing molecular gas reservoir to be consumed at the current star formation rate (ΣH₂/ΣSFR).

Dynamical equilibrium pressure (PDE): The total mid‐plane pressure in a galactic disc balancing gravity from stars and gas against turbulent and thermal support.

References

1. Star Formation Laws and Efficiencies across 80 Nearby Galaxies. The Astrophysical Journal Letters (2023).
2. Probing the Relationship Between Early Star Formation and CO in the Dwarf Irregular Galaxy WLM with JWST. The Astronomical Journal (2024).
3. The ALMaQUEST Survey XI: a strong but non-linear relationship between star formation and dynamical equilibrium pressure. Monthly Notices of the Royal Astronomical Society (2023).
4. Carbon monoxide in an extremely metal-poor galaxy. Nature Communications (2016).