Study Finds Spiral Galaxies Are Bigger Than Previously Thought

Posted on June 29, 2013

M74 spiral galaxy


A new University of Colorado Boulder study has found that spiral galaxies are larger and more massive than previously believes. A NASA image of the M74 Galaxy is pictured above. Hubble has a picture galaxy of M74 here.

CU-Boulder Professor John Stocke, the leader of the study, said in a release that new observations with Hubble's Cosmic Origins Spectrograph (COS) show that normal spiral galaxies are surrounded by halos of gas that can extend to over 1 million light-years in diameter. The current estimated diameter of the Milky Way is about 100,000 light-years. The material for galaxy halos detected by the CU-Boulder team was originally ejected from galaxies by exploding stars known as supernovae.

Stocke says, "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. 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."

The research team used distant quasars -- the swirling centers of supermassive black holes -- as "flashlights" to track ultraviolet light as it passed through the extended gas halos of foreground galaxies.

Stocke says, "This gas is way too diffuse to allow its detection by direct imaging, so spectroscopy is the way to go."

Image: NASA