Telescope finds ‘interstellar tunnel’ within our solar system’s hot bubble

Our solar system resides within a bubble of superheated gas known as the Local Hot Bubble (LHB). Scientists have long pondered its origins.

To better study this region, the Max Planck Institute for Extraterrestrial Physics (MPE) researchers used data from the eROSITA All-Sky Survey.

And they spotted a fascinating feature within the LHB: an interstellar tunnel towards the constellation Centaurus. This tunnel may connect our local bubble to neighboring superbubbles, forming a vast network of hot gas.

“The highlight of this work features the discovery of a new interstellar tunnel towards the constellation Centaurus, potentially joining our LHB with a neighboring superbubble,” the authors noted in the press release.

Supernova explosion role

Our solar system is situated inside a vast, 1,000-light-year-wide cavity, Local Hot Bubble. This idea was first introduced about 50 years ago.

This bubble is a rarified region of interstellar space, much less dense than the surrounding medium. Moreover, the hot bubble is filled with a tenuous, million-degree gas emitting soft X-rays.

Astronomers have analyzed data from the eROSITA X-ray telescope to map the LHB’s structure and properties in unprecedented detail.

Scientists believe that supernova explosions over millions of years carved out this cavity.

As per the press release, the eROSITA data uncovered a large-scale temperature difference within the bubble. This suggests that past supernova explosions may have heated and expanded the bubble, creating a complex and dynamic environment.

“What we didn’t know was the existence of an interstellar tunnel towards Centaurus, which carves a gap in the cooler interstellar medium (ISM). This region stands out in stark relief thanks to the much-improved sensitivity of eROSITA and a vastly different surveying strategy compared to ROSAT,” said Michael Freyberg, the study author, who was part of the ROSAT.

Although the tunnel is intriguing, the current understanding is limited. Additionally, observations of the tunnel are complicated by the presence of another enormous structure located above the galactic center.

Studying x-ray emission

While the LHB is indeed incredibly hot, reaching temperatures of around a million Kelvin, its low density prevents it from significantly heating objects within it.

This is because the atoms in the LHB are spread out over vast distances, making collisions between particles relatively rare.

Despite its low density, the extreme temperature of the gas causes it to emit X-rays.

As per Science Alert, this X-ray emission is what astronomers detected, leading to the discovery of the LHB decades ago.

One significant challenge in studying the LHB is the interference from Earth’s atmosphere.

The geocorona, a diffuse halo of hydrogen gas extending far beyond Earth’s surface, can interact with the solar wind, producing soft X-rays. This X-ray emission can mimic the signal from the LHB, making it difficult to isolate and study.

To overcome this challenge, astronomers need to observe the X-ray sky from a distance far enough to avoid the geocorona’s influence. The eROSITA telescope’s position in space proves advantageous in this case.

eROSITA is located 1.5 million kilometers from Earth. From this position, the telescope can provide a clearer, more accurate view of the LHB and other celestial X-ray sources. Further observations may provide more insights on LHB.

The study was published in the journal Astronomy & Astrophysics.