This Hubble Space Telescope image released by NASA and the European Space Agency on February 28, 2006, shows the spiral galaxy of the Messier 101. (Photo : Reuters)
Spiral galaxies may be much larger and more massive than previously believed, researchers at the University of Colorado Boulder reported in a new study conducted using the Hubble Space Telescope.
Study leader John Stocke said new observations with Hubble's $70 million Cosmic Spectograph (COS) designed by the university show that normal spiral galaxies are in fact surrounded by halos of gas that can extend to over 1 million light-years in diameter.
In comparison, the current estimated diameter of the Milky Way is approximately 100,000 light-years.
The material for the galaxy halos was originally ejected from galaxies by exploding stars, a product of the star formation process, Stocke explained.
"This gas is stored and then recycled through an extended galaxy halo, falling back onto the galaxies to reinvigorate a new generation of star formation," he said, adding that, in many ways, "this is the 'missing link' in galaxy evolution that we need to understand in detail in order to have a complete picture of the process."
Building on earlier studies identifying oxygen-rich gas clouds around spiral galaxies by other scientists, Stocke and his colleagues determined that such clouds contain almost as much mass as all the stars in their respective galaxies.
"This was a big surprise," Stocke said. "The new findings have significant consequences for how spiral galaxies change over time."
Additionally, the team of researchers discovered giant reservoirs of gas estimated to be millions of degrees Fahrenheit enshrouding the spiral galaxies and halos under examination. The halos of spiral galaxies, in contrast, were just tens of thousands of degrees.
Shull, a professor at the university's astrophysical and planetary sciences department and a member of the school's Center for Astrophysics and Space Astronomy emphasized that the study of such "circumgalactic" gas is still in its infancy.
