Our solar system sits in a cosmic bubble of hot, sparse gas called the Local Hot Bubble. This region, formed by ancient supernovas, spans 300 light-years and contains gas heated to a million degrees Kelvin.

Within this bubble, we're currently passing through a denser pocket called the Local Fluff. This cooler, denser region offers a unique glimpse into the interplay between our solar system and the surrounding interstellar medium.

The Local Hot Bubble and Local Fluff

Structure of Local Hot Bubble

• Region of hot, low-density gas surrounding our solar system
  • Spans about 300 light-years in diameter
  • Gas heated to roughly 1,000,000 K
  • Contains around 0.001 atoms per cm³
• Exhibits an irregular, non-uniform shape
  • Distances to its boundaries vary in different directions (Orion vs Aquila)
• Presence of hot gas confirmed through X-ray observations (Rosat, Chandra telescopes)
• Primarily composed of hydrogen and helium
  • Small quantities of heavier elements like carbon, nitrogen, oxygen also present
• Forms part of the larger interstellar medium

Origin of Local Hot Bubble

• Formed as a result of multiple supernova explosions
  • Violent deaths of massive stars approximately 10-20 million years ago (Antares, Betelgeuse)
• Supernova shock waves heated and compressed the interstellar gas
  • Generated the hot, rarefied conditions within the LHB
• Stellar winds from nearby stars also played a role in shaping the LHB
  • Constant flow of charged particles ejected from stars (Solar wind, Wolf-Rayet stars)
• Current expansion of the LHB counterbalanced by pressure from the ambient interstellar medium

Local Fluff vs Local Hot Bubble

• Local Fluff (LF) is a denser pocket of interstellar gas embedded within the LHB
  • Our solar system presently traversing through the LF
• LF exhibits a lower temperature compared to the enveloping LHB
  • Around 7,000 K in the LF
  • Significantly cooler than the 1,000,000 K in the LHB
• LF possesses a higher density relative to the LHB
  • Roughly 0.1 atoms per cm³ in the LF
  • 100 times more dense than the LHB (0.001 atoms/cm³)
• LF primarily consists of neutral hydrogen atoms
  • LHB predominantly composed of ionized gas
• LF likely a surviving remnant of an interstellar cloud that endured the LHB's formation
  • Represents a cooler, more concentrated region within the hot, diffuse LHB (Molecular clouds, Bok globules)

Interstellar Matter and Solar System Interaction

• The heliosphere marks the boundary where the solar wind interacts with interstellar matter
• Cosmic rays, high-energy particles from space, interact with the heliosphere and Earth's atmosphere
• Spectroscopy allows for the study of interstellar matter through absorption lines in stellar spectra
• Interstellar dust particles play a role in light absorption and scattering in space