LOCAL BUBBLE

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 Solar System has been travelling through the Local Bubble for the last 3 million years. Its current location lies in the Local Interstellar Cloud or Local Fluff, 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.
Most astronomers believe that the Local Bubble was formed between some hundreds of thousands to a few million years ago by nearby supernovae that pushed aside gas and dust in the local ISM leaving behind hot, low density material. The most likely candidate for the remains of this Supernova is the Geminga Gemini Gamma ray source, a pulsar in the constellation of Gemini.
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'.

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References

References

★ http://science.nasa.gov/headlines/y2003/06jan_bubble.htm

★ http://science.nasa.gov/headlines/y2004/17dec_heliumstream.htm

★ http://antwrp.gsfc.nasa.gov/apod/ap020210.html

★ http://www.solstation.com/x-objects/chimney.htm

★ Mark Anderson, "Don't stop till you get to the Fluff", "New Scientist" no. 2585, 6 Jan, 2007, pp. 26-30