(ORDO NEWS) — It often seems that when people die, they leave a void behind. In the case of massive stars, this turns out to be physically true.
A new analysis of dense gas drifting between stars in the Milky Way galaxy has revealed the signature of bubbles that expand into space when a massive star goes supernova at the end of its life. These ghostly trails, scientists say, record the history of star deaths and the rotation of the Milky Way.
The space between the stars is not completely empty. Gas drifts in these voids, sometimes gathering into more diffuse clouds, consisting mainly of atomic hydrogen. Stars are born in these clouds when they become dense enough; and when the stars die, they seed these clouds with the elements they have forged in their cores.
However, how these clouds are formed, ordered, and recycled throughout the galaxy is not entirely clear. So a team of astronomers led by Juan Diego Soler at the Italian National Institute of Astrophysics (INAF) in Italy set out to study the structures found in the neutral atomic hydrogen that pervades our galaxy.
The team used data collected from the HI4PI project, a galaxy-wide survey that scanned the sky at radio waves, to map neutral atomic hydrogen throughout the Milky Way.
This is the most detailed study of its kind carried out to date, which makes it possible to determine not only the distribution of hydrogen in the galaxy, but also its speed. By combining this data with a model of the rotation of the Milky Way, researchers can determine the distance to structures in the gas.
Using this data, the team applied an algorithm commonly used to analyze satellite photographs, highlighting subtle structures in hydrogen that could not be seen with the naked eye.
They consisted of an extensive network of thin filaments of gas known as filaments, those close to the disk being mostly perpendicular to the plane of the Milky Way galaxy; those that were not perpendicular appeared to be randomly oriented. At large distances from the disk of the Milky Way, beyond about 33,000 light years, the filaments were mostly parallel to the galactic plane.
The team interpreted these networks as a feedback imprint of supernovae in the Milky Way’s gas.
“Most likely, these are the remnants of numerous supernova explosions that swell gas and form bubbles that burst when they reach the characteristic scale of the galactic plane, like bubbles that reach the surface in a glass of sparkling wine,” said astronomer Ralf Klessen from the University of Heidelberg in Germany.
“The fact that we see mostly horizontal structures in the outer part of the Milky Way, where the number of massive stars is greatly reduced and, accordingly, there are fewer supernovae, suggests that we are registering the contribution of energy and momentum from stars that form gas in our galaxy” .
This, the team says, could be a new probe for understanding the dynamic processes that shaped the Milky Way’s disk, and a tool for conducting galactic archeology – the study of fossils of ancient processes to reconstruct the history of our galaxy.
It also offers a new context for interpreting other phenomena that may be found in the vicinity of the filaments.
“The interstellar medium – the matter and radiation that exists in the space between stars – is governed by the formation of stars and supernovae, the latter being violent explosions that occur in the final stages of the evolution of stars that are more than ten times as massive as the Sun,” says astronomer Patrick Hennebel. from the Saclay Nuclear Research Center in France.
“Supernova associations are very effective in maintaining turbulence and lifting gas in a stratified disk. Finding these filamentous structures in atomic hydrogen is an important step in understanding the process responsible for star formation on a galaxy scale.”
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