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Nature. 2014 Aug 14;512(7513):171-3. doi: 10.1038/nature13525. Epub 2014 Jul 27.

The origin of the local 1/4-keV X-ray flux in both charge exchange and a hot bubble.

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  • 1Department of Physics, University of Miami, Coral Gables, Florida 33124, USA.
  • 2NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA.
  • 3Department of Physics and Astronomy, University of Kansas, Lawrence, Kansas 66045, USA.
  • 4Université Versailles St Quentin; Sorbonne Universités, UPMC Université Paris 06; CNRS/INSU, LATMOS-IPSL, Guyancourt 78280, France.
  • 5The Henry A. Rowland Department of Physics and Astronomy, Johns Hopkins University, Baltimore, Maryland 21218, USA.
  • 6GEPI Observatoire de Paris, CNRS UMR 8111, Université Paris Diderot, 92190, Meudon, France.
  • 7Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, Michigan 48109, USA.
  • 8Department of Physics, University of Wisconsin, Madison, Wisconsin 53706, USA.
  • 91] NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA [2] Space Sciences Laboratory, University of California, Berkeley, California 94720, USA.


The solar neighbourhood is the closest and most easily studied sample of the Galactic interstellar medium, an understanding of which is essential for models of star formation and galaxy evolution. Observations of an unexpectedly intense diffuse flux of easily absorbed 1/4-kiloelectronvolt X-rays, coupled with the discovery that interstellar space within about a hundred parsecs of the Sun is almost completely devoid of cool absorbing gas, led to a picture of a 'local cavity' filled with X-ray-emitting hot gas, dubbed the local hot bubble. This model was recently challenged by suggestions that the emission could instead be readily produced within the Solar System by heavy solar-wind ions exchanging electrons with neutral H and He in interplanetary space, potentially removing the major piece of evidence for the local existence of million-degree gas within the Galactic disk. Here we report observations showing that the total solar-wind charge-exchange contribution is approximately 40 per cent of the 1/4-keV flux in the Galactic plane. The fact that the measured flux is not dominated by charge exchange supports the notion of a million-degree hot bubble extending about a hundred parsecs from the Sun.

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