Our solar system isn’t just floating in empty space. It’s nestled within a vast, low-density bubble of X-ray-emitting, million-degree hot gas called the Local Hot Bubble (LHB). Now, using data from the eROSITA All-Sky Survey, astronomers have created a detailed 3D map of this cosmic neighborhood, revealing intriguing features and providing new insights into our place in the Milky Way.
The LHB has been a subject of scientific curiosity for decades, with its existence first proposed to explain background measurements of soft X-rays. These low-energy photons can’t travel far through interstellar space without being absorbed, so the absence of such photons in our immediate solar neighborhood hinted at a bubble of hot plasma displacing the surrounding neutral material.
The eROSITA telescope, launched in 2019, has provided the most comprehensive view of the LHB yet. Orbiting 1 million miles from Earth, it’s the first X-ray telescope to observe the universe from outside our planet’s geocorona, minimizing the noise from Earth’s atmosphere. Furthermore, eROSITA’s observations were collected during a solar minimum, a period of low solar activity, further reducing contamination from the solar wind.
The new 3D map of the LHB, constructed by researchers at the Max Planck Institute of Physics (MPE), revealed a striking temperature gradient. The Galactic North is cooler than the Galactic South, suggesting that the LHB has been reheated by supernova explosions. The team found that the hot gas of the LHB is relatively uniform in density, but it’s stretched toward the poles of the galactic hemisphere, expanding away from the galactic disk where resistance is lower. This is consistent with previous observations, but eROSITA’s new map revealed a previously unknown feature – an interstellar tunnel directed towards the constellation Centaurus.
This tunnel is a channel carved through the cooler interstellar medium, likely created by erupting young stars and powerful stellar winds. The team suspects this tunnel might be part of a network of such channels connecting the LHB to neighboring superbubbles, the massive, expanding bubbles created by multiple supernova explosions. These tunnels are maintained and sculpted by stellar feedback, the collective influence of stellar winds, supernovae, and powerful jets from young stars.
The 3D map also includes a census of supernova remnants, superbubbles, and dust, providing a comprehensive picture of our cosmic neighborhood. It reveals the Canis Majoris tunnel, previously known to connect the LHB with the Gum nebula and another superbubble, GSH238+00+09. The map also shows dense molecular clouds at the edge of the LHB, moving away from us. These clouds were likely formed when the LHB was cleared, sweeping denser material to its extremities. This offers clues about when the sun entered the LHB, which the team estimates to be a few million years ago.
The creation of this 3D map of the Local Hot Bubble is a major step forward in understanding our immediate cosmic environment. It provides new insights into the processes that shape the Milky Way, offering a window into the complex interplay of stars, gas, and energy that defines our galactic home.
