Blown into Being: How a Nearby Supernova Sculpted Our Interstellar Neighborhood

In their study, Zucker et al. investigate the origin of the Cluster of Local Interstellar Clouds (CLIC), a group of about fifteen warm, partly ionized clouds found within roughly 15 parsecs (about 50 light-years) of the Sun. These clouds are not just close—they directly affect our Solar System, influencing cosmic rays and the shape of the heliosphere, the protective bubble formed by the Sun’s solar wind. The clouds all move in a generally consistent direction, which hints that they may have formed together. But what sparked their creation? Zucker and her team explore two main ideas: first, that the CLIC might have formed from radiation around nearby stars (so-called Strömgren spheres), and second, that a nearby supernova explosion may have swept up gas and formed the clouds.

The Local Bubble: A Supernova-Carved Cavity

The first section of the paper introduces the larger region containing the CLIC: the Local Bubble. This is a vast, low-density region in space surrounding the Sun, thought to have been created by a series of supernova explosions millions of years ago. Within this bubble, the CLIC stands out as a structured, moving group of gas clouds. The researchers explain how astronomers use data from instruments like the Hubble Space Telescope to map the properties of these clouds by studying how their gas absorbs ultraviolet light from nearby stars. These data have revealed that while the CLIC consists of distinct clouds, their movements suggest a shared past.

Challenging the Strömgren Sphere Hypothesis

Next, the authors test the idea that the CLIC could have formed due to the influence of nearby hot stars, such as epsilon Canis Majoris (ε CMa), which create giant spheres of ionized gas called Strömgren spheres. These stars emit strong ultraviolet radiation that can ionize surrounding gas, potentially influencing the formation of clouds. Zucker’s team uses data from the Gaia mission to model the 3D positions and motions of these stars and their Strömgren spheres, tracing both backward in time. They find that the CLIC lies well within the largest nearby Strömgren sphere but is moving in a direction that doesn’t match the sphere’s expansion. This misalignment makes it unlikely that the clouds were formed solely by the radiation from such stars.

A Supernova Makes a Stronger Case

Shifting focus, the authors then explore the supernova hypothesis. Specifically, they propose that a supernova that exploded about 1.2 million years ago in the Upper Centaurus Lupus (UCL) region—a part of a nearby group of young stars called the Scorpius-Centaurus OB association—could have formed the CLIC. This explosion would have sent a shockwave into the Local Bubble, sweeping up any leftover gas and forming a shell of material. As this shell expanded, it could have fragmented into the individual clouds that make up the CLIC today. To test this, Zucker and her colleagues created a model simulating the expansion of such a shell and compared it to the positions and motions of the CLIC clouds.

Modeling a Supernova’s Expanding Shell

Their results show that this model fits well: the current speeds and positions of the clouds are consistent with them having been formed by a shockwave moving through a low-density environment. The variation in speeds among the clouds can be explained by the idea that they were “picked up” by the expanding shell at different times. The team also includes a term in their model to account for the slowing down (or deceleration) of the clouds over time, which happens as they push through the thin gas inside the Local Bubble.

Matching Predictions with Observations

Finally, the authors use their model to make predictions about the CLIC’s physical properties. They estimate that the clouds formed over the last million years and that their structure and motion are best explained by this supernova origin. Their model also predicts features such as the column density (a measure of how much gas is along the line of sight), the clouds’ temperatures, and even the way magnetic fields might be arranged within the complex. While some uncertainties remain—such as the exact gas density in the Local Bubble—the supernova explanation provides a strong match to the data.

A New Origin Story for Our Interstellar Environment

In summary, Zucker et al. present compelling evidence that the CLIC wasn’t shaped merely by starlight, but by the powerful and chaotic aftermath of a supernova explosion. This explosion, which likely occurred within our interstellar backyard, helped sculpt the very clouds we now find ourselves drifting through—offering a dramatic example of how cosmic events continue to shape the environment around our Solar System.

Source: Zucker