The story of the local bubble

Our solar system is located in the middle of a relatively empty region of space: the “local bubble”. There are fewer atoms and molecules here than elsewhere between stars. Astronomers have now discovered how this bubble, about a thousand light years in diameter, formed and how it grew over time. Accordingly, the region was formed millions of years ago by the force of numerous star eruptions and is still expanding today. According to scientists in the journal Nature, there may be many similar bubbles in the Milky Way.

Catherine Zucker of Harvard University in the United States explains, “We have known for decades that our solar system is in a thin and hot gas-filled region. However, it is not yet clear how and when the local bubble formed.” Evaluating data from the European Gaia Space Telescope, it showed that within 500 light-years from the surface of the bubble, almost all star-forming regions formed there – and the researchers conclude that the bubble is enlarging.

Using the speed of the stars, Zucker and his colleagues calculated that the bubble formed about 14 million years ago. “There must have been about 15 supernova eruptions in the region at that time,” Zucker said. The high energy radiation of these galaxy explosions blows the surrounding gas, forming a bubble. On the expanding surface of the bubble, the pressure of the explosions pushes the gas together, allowing new stars to form. This process continues to this day: the team has identified areas where seven stars form on the surface of the bubble, which still expands at a speed of seven kilometers per second. “It helps to first explain why new stars form near the Sun,” says Zucker.

By the way, our sun is not part of this process. When the first stars exploded in this area, it was still a long way off. Only five million years ago our solar system penetrated the interior of the bubble in its orbit through the Milky Way. Today the sun is approximately in the middle of the structure. It is a blessing for astronomers as they can read the local bubble in great detail from this position. In the future, Zucker and his team will want to look for similar bubbles in the Milky Way and explore how different bubbles touch each other and how they affect each other. More needs to be learned about the role of these regions in galaxy evolution.