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The Local Bubble is a cavity in the interstellar medium (ISM) of the Orion Arm of the Milky Way. It is at least 300 light years across and has a neutral hydrogen density approximately one tenth of the 0.5 atoms per cubic centimetre average for the ISM in the Milky Way. The hot diffuse gas in the Local Bubble emits X-rays. The very sparse, hot gas of the Local Bubble is the result of supernovae that exploded within the past two to four million years.[1] The most likely candidate for the remains of this supernova is "Geminga" ("Gemini gamma-ray source"), a pulsar in the constellation Gemini.
The Solar System has been travelling through the region currently occupied by the Local Bubble for the last five to ten million years.[1] Its current location lies in the Local Interstellar Cloud a minor region of denser material within the Bubble. The cloud formed where the Local Bubble and the Loop I Bubble met. The gas within the LIC has a density of approximately 0.1 atoms per cubic centimeter.
The Local Bubble is not spherical, but seems to be narrower in the galactic plane, becoming somewhat egg-shaped or elliptical, and may widen above and below the galactic plane, becoming shaped like an hourglass.
The Local Bubble abuts other bubbles of less dense ISM, including, in particular, the Loop I Bubble. The Loop I Bubble was created by supernovae and stellar winds in the Scorpius-Centaurus Association, some 500 light years from the Sun. Other bubbles abutting the Local Bubble are the Loop II Bubble and the Loop III Bubble.
The Loop I Bubble contains star Antares (also known as Alpha Scorpii) as shown on the diagram above right.
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Earth's location in space |
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| Each arrow should be read as "within" or "part of". |
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