Is there life in nearby galaxies

How stars form in nearby galaxies

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December 25, 2020, 2:44 p.m.

How stars are formed is still one of the great puzzles in astrophysics. A UZH study is re-analyzing previous observation data and comes to the conclusion: In nearby galaxies, the stars typically form in proportion to the amount of gas present there. This suggests that net gas influx from cosmic distances is the main driver of galactic star formation. A media release from the University of Zurich.



The figure shows the visualization of the gas in and around a Milky Way galaxy (center) in today's universe, as predicted by a cosmological simulation by the author.
(Image: Robert Feldmann)
December 22, 2020 - Stars are born in dense clouds of molecular hydrogen gas that permeates the interstellar space of most galaxies. In recent years, the physical understanding of this complex process has improved significantly. However, what is ultimately the trigger for star formation in the galaxies remains an open question.

In principle, two main factors influence the formation of stars: the amount of molecular gas available in the galaxies and the speed with which existing interstellar gas is converted into stars. Accurate determination of these main factors, the goal of numerous observations, is therefore of enormous importance. However, there are challenges in analyzing these observations, and current studies show conflicting results. This is also due to the fact that gas masses in many galaxies cannot be reliably measured in view of the current detection limits.

Star formation depends on the entire gas reservoir
In a study by the Institute for Computational Sciences at the University of Zurich, a new approach has now been chosen: The statistical method, which is based on Bayesian modeling, can correctly and without distorting the data into galaxies with undetected amounts of molecular or atomic hydrogen Include analysis. The result shows that molecular and atomic gas in typical galaxies is used up for star formation within 1 and 10 billion years, respectively. In the case of extremely active galaxies - so-called starburst galaxies - on the other hand, much shorter time scales are found.

“The results suggest that the formation of stars actually depends directly on the total gas mass. Star births are therefore determined by the amount of gas that enters or leaves the galaxy from different cosmic distances, ”says Robert Feldmann, professor at the Center for Theoretical Astrophysics and Cosmology at the University of Zurich. The much higher activity in starbursts, however, seems to have a different physical origin, such as intergalactic interactions or instabilities in galactic disks.

Future data analysis on distant galaxies
The present analysis is based on observation data from nearby galaxies. The gas content in distant galaxies across cosmic history could be studied with the Atacama Large Millimeter / Submillimeter Array, the Square Kilometer Array and other observatories. It is therefore crucial to develop further statistical and data science methods in order to be able to accurately map the physical processes in distant galaxies. “This is the only way to fully uncover the secrets of the formation of stars,” says Feldmann.

Literature:
Robert Feldmann. The link between star formation and gas in nearby galaxies. Communications Physics, 7 December 2020. Doi: 10.1038 / s42005-020-00493-0
https://rdcu.be/cbNUP

Illustration of the formation of a star
The figure shows the visualization of the gas in and around a Milky Way galaxy (center) in today's universe, as predicted by a cosmological simulation by the author. Dense, atomic and molecular hydrogen typically forms an extensive disk, here in bluish-purple in the center of the image. Stars (white) are formed all over the gas disk. Additional star formation can take place in satellite galaxies, seen here at the positions above right and below left. Low density hot gas (green and red hues) can be found at great distances, right up to the edge of the halo of dark matter that surrounds the main galaxy (white circle). The picture also shows a large number of dark matter (purple) substructures, most of which are devoid of gas and stars.

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Source: University of Zurich