NASA’s Chandra X-ray Observatory announced yesterday (September 24, 2012) that our Milky Way galaxy – the galaxy containing our sun and several hundred billion other stars – is surrounded by an enormous halo of hot gas that extends several hundred thousand light-years beyond the Milky Way’s outermost visible edges. The artist’s illustration below shows our Milky Way – our island in space – with two of its satellite galaxies, the Small and Large Magellanic Clouds. The halo of gas is shown with a radius of about 300,000 light-years, although it may extend significantly further. Given that the next-nearest galaxy, the Andromeda galaxy, is 2.5 million light-years away … this image makes me feel small.
NASA scientists estimate the mass of the hot-gas halo to be comparable to the mass of all the billions of stars in the Milky Way galaxy. If the size and mass of this gas halo is confirmed, it could be the solution to the “missing-baryon” problem for our Milky Way galaxy.
Bottom line: A halo of hot gas apparently surrounds our Milky Way, according to data released on September 24, 2012 by NASA’s Chandra X-ray Observatory. The hot-gas halo may contain as much mass as all the stars in our galaxy. It appears to extend several hundred thousand light-years beyond our Milky Way’s outermost visible edges.