Halos, Bubbles and Old Explosions

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A newly discovered hot halo, a cosmic fountain and ghostly bubbles produced by an ancient explosion could change the way scientists look at galaxies, including our own Milky Way, astronomers reported today. All three findings pointed to dynamic movement in galaxies and in monstrous galactic clusters, the largest stable structures in the universe. The discovery should enable astronomers to better identify phenomena as they look at new galaxies or take a new look at already known ones. In the case of the Milky Way, astronomers detected a huge, hot gas halo, or corona, that could be as much as 100,000 light-years across, much bigger than earlier scientists theorized. A light-year is about 6 trillion miles, the distance light travels in a year. This halo could extend all the way to the Milky Way's nearest neighboring galaxies, the Magellanic Clouds, scientists said. Astronomers found the halo using NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) satellite to peer beyond the edges of our home galaxy. Above and below the galactic plain, in which Earth and our solar system reside, they detected an extremely thin, hot gas corona, or halo. Invisible to optical devices, the halo can be seen by FUSE as a blue, football-shaped envelope around the galaxy. When these clouds fell in, their edges — composed of ionized oxygen — lit up, much as meteors streak across the sky when they enter Earth's atmosphere, said Kenneth Sembach of the Space Telescope Science Institute. The halo is thin — perhaps 10 billion billion times less dense than air — and hot, possibly 1 million degrees Fahrenheit, Sembach told reporters at a meeting of the American