A Violent Birth
Our solar system is inside a vast cavity in the interstellar medium called the Local Bubble. This structure, stretching roughly 1,000 light-years across, is not a void. It is the remnant of a series of powerful stellar explosions. The story began about 14 million years ago, when the first of at least 15 supernovae detonated. These explosions came from massive stars within the Scorpius-Centaurus stellar association.
Over millions of years, the shockwaves from these successive supernovae blasted through space. They pushed and swept up the surrounding interstellar gas and dust, like a snowplow clearing a road. This process carved out the low-density interior of the bubble and piled the collected material into a dense, expanding shell. The gas inside the bubble is incredibly tenuous, with a density about one-tenth of the average for the Milky Way, and heated to roughly 1 million degrees Kelvin. The bubble is not perfectly spherical; data suggests it has an irregular, peanut-like shape that might be wider above and below the galactic plane.
Our Sun is a newcomer to this scene. It was far from the initial explosions when they occurred. By chance, the solar system's path through the galaxy brought it into the Local Bubble about 5 million years ago. Currently, our system sits near the bubble's center.
A Cradle for New Stars
The violent events that created the Local Bubble also triggered star formation. The bubble's expanding surface, where all the swept-up gas and dust has accumulated, is the site for all nearby star formation. As the shockwave plowed into the interstellar medium, it compressed the gas, creating the conditions necessary for gravitational collapse and the birth of new stars.
All young stars and star-forming regions within about 500 light-years of Earth are located on the surface of this bubble. This includes well-known molecular clouds and stellar nurseries. The expansion of the bubble is what drives this ongoing star formation. Astronomers have used data from the Gaia space observatory to create detailed 3D maps of the bubble, tracing the motions of young stars on its shell and confirming their outward expansion from a common origin point.
The bubble itself is still growing, though it has slowed considerably. The shockwave now expands at about four miles per second (roughly 6.7 kilometers per second). Our solar system will not remain inside forever. Its galactic journey will likely carry it out of the Local Bubble in another five million years or so.