The sun is right in the middle of a giant galactic bubble

After decades of research, a chart has finally been established that tells the story of the stars around the Earth. The neighboring stars would be on a kind of bubble created by supernovae from the beginning of the universe.

We all live in a bubble. Literally. That is at least the conclusion of a study published in Nature on 12 January 2022, which looks at the origin of the Milky Way. The authors reconstructed the history of star formation around the Earth to discover that the stars are not where they are at random, but as a result of a series of events that led to the creation of a structure nicknamed the local bubble.

We have traced the positions and movements of young near-Earth stars through a millenniumtells Numerama lead author Catherine Zucker. This is where we discovered a common origin for all these stars associated with supernovae. »

The artist's impression of the local bubble
The artist’s impression of the local bubble. Credit: Leah Hustak

The astronomer from the Space Telescope Science Institute in Baltimore performed 3D simulations to go back in time and find out how stars were formed. It was first necessary to list the various known clusters, which was made possible thanks to Gaia’s star catalog. The European Space Agency’s satellite, launched in 2013, aims to map the Milky Way accurately and published the last volume of its catalog in December 2020 (a new version should arrive within the next few months). With all this data, the scientists were able to enter them into software to create a detailed 3D map of the motion of all these stars.

A chain reaction since the Big Bang

They then noticed that supernovae, these explosions of massive stars, had taken place in a chain since the beginning of the universe, shortly after the Big Bang, and then caused a shock wave, which swept the interstellar clouds of gas and dust. This material then found itself frozen as a thin more or less spherical layer that evoked a bubble. The theory has been present for decades among astrophysicists, but it is the first time that it has been proven with such certainty.

Catherine Zucker continues: The surface of this bubble is an ideal position for the formation of stars: it is a dense shell with many molecular clouds, and that is where stars like our sun can be born. »

In addition, the study shows that this local bubble, about 500 light-years in radius, would not be unique, but would have many equivalents throughout the Milky Way and beyond. Bubbles on the surface of which stars could multiply. In the press release accompanying the newspaper, one of the authors compares the universe to an Emmentaler cheese with holes! Each hole corresponds to a bubble, and it is just around the corner that the stars multiply.

The sun is right in the middle of a giant galactic bubble
The Milky Way. // Source: Public domain

But this ideal breeding ground was not formed from one day to the next. It took about fifteen supernovae to create our local bubble. ” We think there was a supernova every million years or so, details Catherine Zucker. Each has fueled the expansion of the local bubble, and we have identified certain clusters that are at the site of the explosions. These “star nurseries” are well known today and have helped writers track the expansion of the bubble. These are subgroups of stars, named Haut-Centaure-Loup or Bas-Centaure-Croix, and where all stars are approximately the same age.

And in the middle, the Sun.

The beginnings of the creation of this local bubble may be very old, but the structure continues to evolve. Simulations show that the last large-scale supernovae took place just a few million years ago, and the shock is still felt today. Although we are far from the final bouquet of fireworks, the bubble continues to expand at a speed of about 6.5 kilometers per second.

And the Sun in all this? Would it also be on the surface of the local bubble like the other stars nearby? Well no, it’s right in the center. A place he would only have achieved by chance during his birth and his “journey” through the galaxy. But this apparent chance remains rich in lessons, according to Catherine Zucker: ” This proves to us that our Bubble interacts with the others around. This is something we already suspected and which we will dig into as we try to find out more about other similar structures around. The fact that our sun is at the center of the bubble tends to prove that these structures are abundant in our Milky Way.

There are many challenges left when we identify the other structures, recognizes Catherine Zucker, especially around the age of these bubbles, which is difficult to determine. “Information that will be even harder to gather when looking at more distant and less easily observable star clusters. But the authors rely heavily on future Gaia revelations. The full version of the 2020 catalog is expected to arrive soon, and it will provide shifts of 30 million stars, which would be a significant addition to knowing in more detail the origin of our galaxy.

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