Spiral Galaxies Larger Than Thought
June 27, 2013

Spiral Galaxies Like The Milky Way Much Larger Than We Thought

Lee Rannals for redOrbit.com - Your Universe Online

Astronomers now say spiral galaxies like the Milky Way galaxy are actually larger than previously thought.

Scientists from several universities used the Hubble Space Telescope to determine that normal spiral galaxies are surrounded by halos of gas that can extend to over one million light-years in diameter. With this new estimate, it brings the Milky Way from just 100,000 light-years across to roughly 1,100,000 light-years.

The material for the galaxy halos was ejected from galaxies by exploding stars, or supernovae.

"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," said John Stocke of University of Colorado at Boulder's astrophysical and planetary sciences department.

"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 researchers determined that these clouds must contain almost as much mass as all the stars in their respective galaxies.

"This was a big surprise," said Stocke. "The new findings have significant consequences for how spiral galaxies change over time."

Stock and his colleagues discovered giant reservoirs of hot gas estimated to be millions of degrees Fahrenheit that were enshrouding the spiral galaxies and halos under study. The halos of the spiral galaxies were relatively cool by comparison.

Michael Shull, professor at CU-Boulder's Department of Astrophysical and Planetary Sciences, said it should be possible to confirm these early detections, elaborate on the results and scan other spiral galaxies in the universe.

"This gas is way too diffuse to allow its detection by direct imaging, so spectroscopy is the way to go," explained Stocke. CU-Boulder's James Green led the design team, which was built for NASA by Ball Aerospace & Technologies Corp. of Boulder.

The team had to use the Hubble's $70-million Cosmic Origins Spectrograph (COS) for the study. Theoretical studies have shown in the past how spiral galaxies could possess about five times more gas than what was being detected, and Hubble's COS has finally allowed astronomers to finally back up some of these theories with hard data.

"Once Hubble ceases to function, we will lose the capability to study galaxy halos for perhaps a full generation of astronomers," said Stocke. "But for now, we are fortunate to have both Hubble and its Cosmic Origins Spectrograph to help us answer some of the most pressing issues in cosmology."

A 2012 study predicted that the Milky Way was about 20 percent larger than previously believed. This team used measurements of the galactic rotation velocity in the solar system to determine that our galaxy was bigger than previous estimates.