How stars are produced in galaxies nearby

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A major open question remains how stars shape in galaxies. Using a data-driven re-analysis of observational measurements, Robert Feldmann sheds new light on this theme.

In thick clouds of molecular hydrogen gas permeating the interstellar space of most galaxies, stars are born.

While star formation physics is complex, substantial progress has been made in the understanding of star formation in the galactic environment in recent years.

It remains an open question, however, what actually determines the degree of star formation in galaxies.

In general, the activity of star formation is determined by two key factors: the amount of molecular gas present in galaxies and the time scale on which conversion to stars depletes the gas reservoir.

Although competition between gas inflows, outflows, and consumption governs the gas mass of galaxies, the physics of gas-to-star conversion is not well understood at present. Given this potentially critical position, several attempts have been made via observations to determine the timescale of gas depletion. However, owing in part to the difficulty of accurately measuring gas masses given current detection limits, these attempts have produced contradictory results.

The total gas reserve is correlated with normal star formation.
To correctly account for galaxies with undetected concentrations of molecular or atomic hydrogen, the present analysis uses a modern statistical approach based on Bayesian modeling, reducing observational errors.

This new research shows that molecular and atomic hydrogen are transformed to stars over roughly constant timescales of 1 and 10 billion years, respectively, in typical star-forming galaxies. Very active galaxies (starbursts) have much shorter gas depletion timescales, however.

These findings indicate that star formation is also directly related to the total gas reservoir in typical galaxies and is thus dictated by the rate at which gas enters or leaves a galaxy.

The significantly greater star formation behavior of starbursts, on the other hand, is likely to have a different physical cause, such as galaxy interactions or galactic disk instability.

This study is based on data from nearby galaxies for observation. Observations promise to measure the gas content of a vast number of galaxies across cosmic history with the Atacama Large Millimeter/submillimeter Array, the Square Kilometer Array, and other observatories.

To accurately extract the physical content from these fresh observations and fully reveal the secrets of star formation in galaxies, it will be important to continue improving statistical and data science methods.

“Reference: “The relation between star formation and gas in surrounding galaxies” by Robert Feldmann, Communications Physics, December 7, 2020. DOI: 10.1038/s42005-020-00493-0. DOI: 10.1038/s42005-020-00493-0.

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