How Supernova Explosions May Have Stopped Star Formation Near the Sun
Astronomers have long been fascinated by the Local Bubble (LB), a giant, low-density cavity in the interstellar medium that surrounds our solar system. It is thought to have formed from the combined energy of many supernovae (the explosive deaths of massive stars). Previous studies estimated that the LB was about 14 million years old and powered by roughly 15–20 supernovae. However, in earlier work, Leonard Romano and collaborators (through the SISSI simulation project) suggested that the bubble might actually be younger than that. In this follow-up study, Romano directly compares detailed 3D maps of dust around the Sun with supernova simulations to better constrain the bubble’s history.
Geometry of the Local Bubble
To understand how big the LB is and how much material it has swept up, Romano applies statistical techniques to the 3D dust maps. This allows him to reconstruct the bubble’s size, density, and momentum, essentially how much “push” the expanding bubble carries. The study finds that the LB has a radius of about 210 parsecs (roughly 700 light-years) and a relatively low average gas density. Importantly, the analysis also provides the first estimate of the LB’s momentum, which helps constrain how many supernovae were needed to drive its expansion.
The Age of the Local Bubble
The bubble’s age depends on both how many supernovae exploded and how quickly their combined energy expanded into space. Romano compares the observed properties of the LB to results from high-resolution SISSI simulations of supernova remnants evolving in a realistic galactic environment. The analysis shows that the LB cannot be as old as previously thought. Instead of 14 million years, the bubble is only about 3.5–5.5 million years old. To reach its current size and momentum in that short time, it must have been powered by around 19–30 supernovae, far more than earlier studies suggested.
This result also creates tension with the long-held idea that the LB was powered only by explosions in the nearby Scorpius-Centaurus OB association, a group of young stars near the Sun. The timing of star formation there doesn’t align with the new age estimate for the LB. Instead, Romano suggests that the LB might be linked to the larger Alpha Persei family of star clusters, which shows a history of episodic star formation over the last 60 million years.
Implications for Local Star Formation
One of the most striking conclusions of the paper is that the LB may not have triggered new star formation, as some previous researchers suggested. Instead, its rapid expansion may have actually quenched star formation, essentially shutting it down, in the solar neighborhood. This would mean that famous nearby star-forming regions, like Taurus or Sco-Cen, likely formed before the LB began expanding and were not directly created by it. The paper even suggests that the timing of recent declines in local star formation lines up with the onset of the LB’s expansion.
Concluding Remarks
Romano’s study reshapes our understanding of the Local Bubble by making it both younger and more powerful than earlier estimates. Instead of a quiet structure inflated slowly over 14 million years, the LB now appears to be a dynamic feature only a few million years old, fueled by a burst of supernovae. While the results raise new questions, such as which stellar groups exactly contributed to its creation, they also suggest that the Local Bubble may have suppressed star formation near the Sun rather than promoting it. Future models and more precise stellar ages will help resolve these uncertainties.
Source: Romano
