The orbiting Chandra X-ray observatory has detected the first definite evidence for a giant halo of hot gas around a spiral galaxy much like our own Milky Way.

The discovery may lead to a better understanding of our own star system, as well the structure and evolution of galaxies in general.

The astronomers observed the spiral galaxy NGC 4631 which is about 25 million light-years from Earth with both Chandra and the Hubble Space Telescope.

Previous observations of NGC 4631 have detected diffuse X-ray emission from it and other spiral galaxies. However, Chandra's detailed view enables astronomers to be able to separate the individual X-ray sources in the galaxies from the diffuse halos.

Chandra found the diffuse halo of X-ray gas in NGC 4631 to be radiating at a temperature of almost three million degrees and extending some 25,000 light-years from the galaxy.

'Gas outflows'

"Scientists have debated for over 40 years whether the Milky Way has an extended corona, or halo, of hot gas," said Daniel Wang of the University of Massachusetts, US.

"Of course since we are within the Milky Way, we can't get outside and take a picture. However, by studying similar galaxies like NGC 4631, we can get an idea of what's going on within our own galaxy."