Interstellar tunnel found near our solar system—may be a gateway to other stars

The solar system drifts inside an immense, low-density cavity known as the Local Hot Bubble (LHB). This region, spanning at least 1,000 light-years, radiates X-rays due to its searing million-degree temperature. Yet, because its atoms are so sparse, this extreme heat has little effect on the matter within. While this has allowed life on Earth to thrive undisturbed, the LHB itself has remained an astronomical mystery.

Scientists believe that long-ago supernova explosions sculpted this vast bubble, blasting away surrounding interstellar gas. A sequence of stellar detonations likely carved out the region, leaving behind a hot, X-ray-emitting void. However, only recently have researchers begun to map its true shape and structure in detail.

A team at the Max Planck Institute for Extraterrestrial Physics (MPE), led by astrophysicist Michael Yeung, has now provided an unprecedented look at the LHB.

Using the eROSITA X-ray telescope, they created the most detailed map of this cosmic bubble yet. Positioned 1.5 million kilometers from Earth, eROSITA avoids interference from Earth's hydrogen halo, giving it a pristine view of the X-ray sky.

To analyze the bubble’s structure, researchers divided the sky into 2,000 segments, examining X-ray emissions in each. Their findings revealed that the LHB isn’t a uniform sphere. Instead, it expands more easily perpendicular to the galactic plane, where it faces less resistance compared to the dense horizontal disk of the Milky Way.

Michael Freyberg, an MPE scientist, compared the bubble’s shape to a bipolar nebula but noted key differences. “It’s spikier and bumpier,” he explained. This irregularity suggests that the LHB's evolution was influenced by multiple factors beyond simple supernova explosions.

One of the study’s biggest surprises was an interstellar tunnel extending toward the constellation Centaurus. This previously unknown gap in the cooler interstellar medium appears to act as a passageway, allowing hot gas from the LHB to escape.

"What we didn’t know was the existence of an interstellar tunnel towards Centaurus, which carves a gap in the cooler interstellar medium," Freyberg said.

The tunnel isn’t just an isolated feature. The team's model revealed a temperature gradient within the LHB, with the northern region being hotter than the southern. This suggests that recent supernova events may have reheated parts of the bubble within the last few million years.

The LHB has fascinated astronomers since its existence was proposed over fifty years ago. Initially, scientists used the bubble to explain mysterious X-ray emissions that shouldn’t have reached us through the dense interstellar medium. The theory gained traction as observations revealed a relative void of interstellar dust near our solar system.

Challenges emerged in the 1990s when scientists discovered that solar wind interactions with Earth’s geocorona could also produce X-rays. But recent data from eROSITA, which observed the sky during a solar minimum, confirmed the LHB's role in these emissions.

Michael Yeung highlighted eROSITA’s contribution, stating, "eRASS1 data provides the cleanest view of the X-ray sky to date, making it the perfect instrument for studying the LHB."

The detailed 3D model constructed by Yeung’s team paints a vivid picture of our cosmic neighborhood. It includes known supernova remnants, molecular clouds, and even other tunnels, like the Canis Majoris tunnel, potentially linking the LHB to the Gum Nebula.

Some dense molecular clouds near the bubble’s edge have velocities suggesting they formed from material swept up during the bubble’s early formation. Co-author Gabriele Ponti noted, "The sun must have entered the LHB a few million years ago—a short time compared to the age of the sun."

This central positioning of the Sun within the LHB is purely coincidental. As the solar system moves through the Milky Way, we’re likely just passing through this cosmic cavity.

The discovery of the Centaurus tunnel could mark the beginning of a new chapter in galactic exploration. If the Milky Way is indeed a vast network of hot bubbles and tunnels, studying these structures could reveal the galaxy’s dynamic history.

The study, published in Astronomy & Astrophysics, emphasizes how stellar feedback—energy released by dying stars—shapes the interstellar medium. As researchers continue to analyze eROSITA’s data, we may soon uncover more secrets hidden in the vast expanse of space.

Superbubbles are vast cavities in space filled with hot, low-density gas, often created by the combined activity of supernovae and stellar winds from massive stars. The LHB above is the closest superbubble to Earth. The next nearest superbubbles are:

These superbubbles play a significant role in shaping the structure of the Milky Way, influencing star formation and the dynamics of interstellar gas.

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