Interstellar tunnel discovered near our solar system – could lead to other star systems

Our solar system resides in a unique low-density bubble called the Local Hot Bubble (LHB). Stretching at least 1,000 light-years, this region glows in X-rays due to its million-degree temperature. However, because its atoms are so sparse, this extreme heat barely affects the matter inside. It’s fortunate for life on Earth, but this enigmatic bubble has long puzzled astronomers.

Theories suggest that the LHB was carved out millions of years ago by supernova explosions. A chain of these stellar detonations likely blew away the interstellar medium, creating this expansive cavity. Recent breakthroughs from the Max Planck Institute for Extraterrestrial Physics (MPE) have shed light on the LHB's true nature and its intricate structure.

Astrophysicist Michael Yeung and his team used eROSITA, a powerful X-ray telescope aboard a space observatory, to map the LHB in unprecedented detail. Unlike Earth-based observatories or those influenced by our planet's halo of hydrogen, eROSITA operates 1.5 million kilometers from Earth. This unique vantage point offers an untainted view of the X-ray sky.

By dividing the sky into 2,000 sections, researchers analyzed the X-ray light in each area. They discovered that the LHB is not a uniform sphere but expands more readily perpendicular to the galactic plane. This makes sense—there’s less resistance in the vertical direction compared to the horizontal galactic disk.

Michael Freyberg, another key member of the MPE team, noted that the bubble's shape resembles a bipolar nebula, though spikier and bumpier. This irregular structure wasn’t the only revelation. "What we didn't know was the existence of an interstellar tunnel towards Centaurus, which carves a gap in the cooler interstellar medium," Freyberg explained.

This tunnel could connect the LHB to a neighboring superbubble or other cosmic structures like the Gum Nebula. Its discovery lends credence to a 1974 theory proposing that the galaxy consists of interconnected hot bubbles and tunnels. Though evidence for such a network has been scarce, this finding could be a crucial piece of the puzzle.

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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