Voids Created By Dying Stars Have Been Detected In Our Galaxy’s Interstellar Gas

It often feels like when people die they leave a void behind. In the case of massive stars, this happens to be physically true.

A new analysis of the tenuous gas drifting between stars in the Milky Way galaxy has revealed the imprint of expanding bubbles in space when a massive star goes supernova at the end of its life. These ghostly traces, say the scientists, record a history of dying stars and rotating the Milky Way.

The space between the stars is not entirely empty. In these interstices of space gas drifts, sometimes gathering into more diffuse clouds, mostly of atomic hydrogen. Stars are born in these clouds when they are dense enough; and when they die, the stars seed these clouds with the elements they have forged into their cores.

How these clouds form, arrange, and recycle throughout the galaxy, however, is not fully understood. So a team of astronomers, led by Juan Diego Soler of the Italian National Institute of Astrophysics (INAF) in Italy, set out to study the structures found in the neutral atomic hydrogen that permeates our galaxy.

The team used data collected by the HI4PI projectan all-sky survey that studied the sky in radio wavelengths to obtain a map of neutral atomic hydrogen throughout the Milky Way.

It’s the most detailed survey of its kind to date, mapping not only the galaxy’s hydrogen distribution, but also its velocity. By combining this with a rotational model of the Milky Way, researchers can measure the distance to structures in the gas.

With this data, the team used an algorithm commonly used to analyze satellite photos, detecting fine structures in the hydrogen that would have been impossible to identify with the naked eye.

These consisted of a vast network of fine threads of gas called filaments, those near the disk mostly perpendicular to the plane of the Milky Way galaxy; those that weren’t perpendicular seemed to be oriented randomly. At greater distances from the Milky Way disk, beyond about 33,000 light-years, the filaments were mostly parallel to the galactic plane.

The team interpreted these networks as the imprint of supernova feedback in the Milky Way gas.

“These are likely the remnants of multiple supernova explosions that sweep up gas and form bubbles that burst when they reach the characteristic scale of the galactic plane, like the 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 mainly see 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 input of energy and momentum stars shaping gas in our galaxy.”

According to the team, this could offer a new probe for understanding the dynamic processes that shaped the Milky Way’s disk, and a tool for conducting galactic archeology – studying 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, which is the matter and radiation that exists in the space between stars, is regulated by the formation of stars and supernovae, the latter being the violent explosions that occur during the later evolutionary stages of ‘stars more than ten times more massive than the Sun’, says astronomer Patrick Hennebelle of the Saclay Nuclear Research Center in France.

“Supernova associations are very effective at maintaining turbulence and lifting gas in a stratified disk. The discovery of these filamentous structures in atomic hydrogen is an important step in understanding the process responsible for star formation at the time. scale of the galaxy.”

The research has been published in Astronomy & Astrophysics.