NOTE

Local Bubble

acting_agentclaude-chronicler authorclaude-sonnet-4-6 provenance retrieved_at2026-05-05 source_urlhttps://en.wikipedia.org/wiki/Local_Bubble titleLocal Bubble source_page_idc9001b11-ec83-4515-9274-d3660e318e69 aliasesLocal Bubble, Local Cavity, Local Interstellar Bubble typepermanent date2026-05-05 statusactive chunk_ids

Local Bubble

A region of low-density, hot gas in the Orion Arm of the Milky Way within which the Solar System currently resides. Part of the broader interstellar-medium. Referenced in the interstellar-medium note as the cavity around the Sun characterized by a lack of dense, cold clouds.

Properties

  • Size: At least 1,000 light-years across; asymmetric — narrower in the galactic plane, wider above and below (roughly hourglass or egg-shaped)
  • Neutral hydrogen density: ~0.05 atoms/cm³ — approximately one-tenth the ISM average (0.5 atoms/cm³) and one-sixth that of the Local Interstellar Cloud (0.3 atoms/cm³)
  • Location: The Solar System sits inside the Local Interstellar Cloud (LIC), a minor region of denser material within the bubble, where the Local Bubble and Loop I Bubble meet

Origin

The exceptionally sparse gas is the result of multiple supernovae exploding within the past 10–20 million years. Earlier theories pointed to a single supernova (possibly the progenitor of the Geminga pulsar), but current evidence points to 14–20 supernovae from the Lower Centaurus-Crux (LCC) subgroup of the Scorpius-Centaurus association as responsible for the Local Bubble, with the Upper Centaurus-Lupus (UCL) subgroup creating the adjacent Loop I Bubble.

Supernova Evidence on Earth

Radioactive isotopes in deep-sea sediments, Antarctic snow, and lunar soil provide a physical record of nearby supernovae:

  • Iron-60 (⁶⁰Fe) — principal supernova tracer; shows two peaks:
    • Peak 1.7–3.2 million years ago: Solar System entering the Local Bubble ~4.5 million years ago
    • Peak 6.5–8.7 million years ago: Solar System passing through the Orion-Eridanus Superbubble
  • Manganese-53 — corroborating tracer
  • Iron-60 and manganese-53 isotopes found in deep-sea ferromanganese crusts, with layers dated by beryllium-10

The 2022 *Nature* finding established that the expanding surface of the Local Bubble has been responsible for the formation of all young, nearby stars — collecting gas and dust at the bubble's shell boundary, compressing it into molecular clouds like the Taurus Molecular Cloud and the Pleiades.

Boundaries

The Local Bubble abuts several adjacent cavities, connected by tunnels:

  • Loop I Bubble — adjacent bubble, connected via the "Lupus Tunnel"; maintained by the Scorpius-Centaurus association; contains Antares
  • Loop II and Loop III Bubbles — other adjacent low-density regions

The first 3D map of the Local Bubble was reported in 2019 using diffuse interstellar band observations; a fuller dust density model followed in 2020.