Astronomers find imprint of the bubbles produced by the explosion of dying stars in our galaxy

An international group of astronomers, led by Juan Diego Soler of the Italian National Institute of Astrophysics (INAF), has found the imprint of the bubbles produced by the explosion of dying stars in the structure of the gas permeating our galaxy. They made this discovery by applying artificial intelligence techniques to the HI4PI survey data, which yields the most detailed distribution of atomic hydrogen in the Milky Way across the entire sky to date. The scientists analyzed the wire structure in the emission of atomic hydrogen gas. They concluded that it held a record of the dynamic processes caused by ancient supernova explosions and the galaxy’s rotation. Their results have been published in Astronomy and Astrophysics†

Hydrogen is the main component of stars like the sun. The process by which the diffuse clouds of hydrogen gas that spread throughout our galaxy to collect in dense clouds that eventually form stars is not yet fully understood. A collaboration of astronomers led by Juan Diego Soler of the INAF-IAPS (Istituto di Astrofisica e Planetologia Spaziali, an INAF research institute in Rome) and the ECOgal project has now taken an important step in elucidating the life cycle of the form resource stars.

Soler processed data from the most detailed aerial survey of atomic hydrogen emissions in radio waves, the HI4PI study, which is based on observations obtained with the Parkes 64-meter Radio Telescope in Australia, the Effelsberg 100-meter Radio Telescope in Germany and the Robert C. Byrd Green Bank 110-meter Telescope (GBT) in the United States. “These archival observations of the hydrogen emission line at a wavelength of 21 cm contain information about the distribution of the gas in the air and its velocity in the observation direction, which, in combination with a model of the rotation of the Milky Way, indicates how far the emitting clouds are,” says Sergio Molinari of the INAF-IAPS, principal investigator of the ECOgal project.

To study the distribution of the galactic hydrogen clouds, Soler applied a mathematical algorithm often used in the automatic inspection and analysis of satellite images and online videos. Due to the magnitude of these observations, it would have been impossible to conduct this analysis by eye. The algorithm revealed an extensive and intricate network of slender thread-like objects or filaments. Most of the filaments in the innermost part of the Milky Way were found to point away from our galaxy’s disk.

“These are likely the remnants of multiple supernova explosions that sweep up the gas and form bubbles that pop when they reach the galactic plane’s characteristic shell, like the bubbles that reach the surface in a glass of sparkling wine,” says Ralf Klessen. Klessen is also principal investigator of the ECOgal project, which aims to understand our galactic ecosystem, from the disk of the Milky Way to the formation sites of stars and planets. “The fact that we see mostly horizontal structures in the outer Milky Way, where there is a sharp decrease in the number of massive stars and consequently fewer supernovae, suggests that we are recording the energy and momentum inputs from stars that make up the gas in our galaxy,” says the astronomer from the Center for Astronomy at the University of Heidelberg in Germany.

“The interstellar mediumthe matter and radiation that exists in the space between the stars is regulated by the formation of stars and supernovas, the latter being the violent explosions that occur during the last evolutionary stages of stars more than ten times more massive than the sun” , says Patrick Hennebelle, who, together with Klessen, is coordinating the theoretical work in the ECOgal project. “Associations of supernovas are very efficient in maintaining turbulence and lifting the gas in a layered disk,” clarifies the researcher of the Department of Astronomy at CEA/Saclay in France “The discovery of these threadlike structures in the atomic hydrogen is an important step in understanding the process responsible for galaxy-scale star formation.”