Astronomers have crafted a detailed three-dimensional map of the Local Hot Bubble (LHB), a vast, low-density region surrounding our solar system. This bubble, filled with hot, X-ray-emitting gas, has been a subject of study since the 1970s, and recent data from the eROSITA All-Sky Survey has provided new insights into its structure and history. The eROSITA telescope, which operates as part of the Spectrum-Roentgen-Gamma (SRG) mission, has allowed astronomers to view the bubble with unprecedented clarity by observing X-ray activity from outside Earth’s geocorona.
The new map reveals intriguing temperature variations within the LHB, attributed to stellar winds and supernova explosions. These phenomena cause certain regions of the bubble to expand, providing a more dynamic picture of its evolution. A particular discovery is the identification of an “escape tunnel” directed towards the constellation Centaurus. This tunnel may be a connection to another superbubble in the galaxy, formed by active young stars.
The History of the Local Hot Bubble
The presence of the LHB has been recognised for nearly five decades, and its origins are believed to be linked to supernova activity. Early studies of the bubble were hindered by interference from X-ray emissions within Earth’s atmosphere. However, the eROSITA telescope, launched in 2019, has now provided astronomers with the cleanest X-ray data of the bubble. Michael Yeung, a researcher at the Max Planck Institute, noted that the eRASS1 data, which was collected during a period of low solar wind activity, offers the most precise view of the X-ray sky to date.
The mapping of the Milky Way’s hemisphere into around 2,000 regions has revealed a temperature difference between the Galactic North and South, with the Northern hemisphere being cooler. This discovery hints at an internal temperature disparity within the LHB.
A New Interstellar Tunnel and Its Implications
Along withtemperature variations, the eROSITA data has revealed a previously unknown interstellar tunnel pointing towards the Centaurus constellation. This tunnel appears to connect the LHB with a hot gas corridor in the galaxy, suggesting a larger network of such tunnels across interstellar space.
The team also noted the presence of dense molecular clouds at the edges of the LHB, potentially a remnant of the bubble’s formation. Gabriele Ponti, an MPE scientist, emphasised that the solar system is located in the centre of this bubble, though the Sun entered the LHB only a few million years ago – a brief moment in the Sun’s 4.6-billion-year history.