Our Solar System resides at the center of a massive 1,000-light-year-wide bubble, its bumpy shell actively spawning thousands of new stars. Astronomers' latest study reveals exactly how many supernova explosions sculpted this immense cosmic structure.
About 50 years ago, researchers discovered that Earth and the Solar System lie within a vast cavity called the Local Bubble, where no stars have formed in at least 14 million years. Stars inside either predate the bubble or, like our Sun, formed elsewhere and drifted through it.
Far from spherical, this bubble is irregularly shaped and lumpy, pointing to multiple supernova blasts that cleared out its interior. These explosions propelled material outward, compressing gas to ignite star formation hundreds of light-years away—explaining the interstellar dust we detect nearby.
Now, a study published in Nature quantifies the supernovae required to excavate this cosmic void.
Leveraging data from the European Space Agency's Gaia observatory, scientists crafted a precise 3D map of the Local Bubble's surface. They traced the paths of its seven primary star-forming regions on the shell and measured its expansion at about 6.4 km per second. This allowed them to calculate the necessary supernova count.
"We quantified the momentum driving the Local Bubble's expansion and matched it to the input from supernovae," the authors explain. "Our analysis indicates roughly fifteen supernovae—likely from two distinct star clusters—powered this growth."
Though Earth now anchors the bubble's core, the Sun formed about 1,000 light-years away and entered this structure only 5 million years ago. It will exit in roughly 8 million years.
Per the Copernican principle—which holds that Earth holds no privileged spot in the cosmos—our position suggests these bubbles are commonplace. "These voids likely overlap, with star formation thriving at their boundaries," the researchers note. The Milky Way thus resembles "a Swiss cheese, its holes gouged by supernovae and rimmed with budding stars."
