Image 1 - Sombrero Galaxy Found To Have A Split Personality
April 25, 2012

Sombrero Galaxy Found To Have A Split Personality

The Spitzer Space Telescope has helped astronomers reveal that the Sombrero galaxy is both a rotund and a slender disk galaxy.

Sombrero is a round elliptical galaxy with a thin disk embedded inside, and is one of the first known to exhibit characteristics of two different types of galaxies.

"The Sombrero is more complex than previously thought," Dimitri Gadotti of the European Southern Observatory in Chile, said in a press release. "The only way to understand all we know about this galaxy is to think of it as two galaxies, one inside the other."

The galaxy is 28 million light-years away in the constellation Virgo, and from Earth's vantage-point, it looks like a wide-brimmed hat, helping it earn its name Sombrero.

NASA's Spitzer telescope was able to capture a different view of the galaxy than visible-light telescopes can.  In visible views, Sombrero looks to be immersed in a glowing halo.  However, with Spitzer's vision, old stars are seen through the dust, revealing the halo has the right size and mass to be a giant elliptical galaxy.

Gadotti and colleagues reported in the Monthly Notices of Royal Astronomical Society that a giant elliptical galaxy was inundated with gas more than nine billion years ago.

Early in the history of the universe, networks of gas clouds were common and would sometimes feed the growing galaxies.  This gas would have been pulled into the galaxy by gravity, falling into orbit around the center and spinning out into a flat disk.

"This poses all sorts of questions," Rubén Sánchez-Janssen from the European Southern Observatory, co-author of the study, said in a press release. "How did such a large disk take shape and survive inside such a massive elliptical? How unusual is such a formation process?"

The astronomers believe the answers to these questions could help them piece together how other galaxies have evolved.

The discovery answers a mystery about why so many global clusters lie in the Sombrero galaxy.  Global clusters are spherical nuggets of old stars, and elliptical galaxies typical contain a few thousands, while spiral galaxies contain a few hundred.

The Sombrero contains nearly 2,000 global clusters, which is a number that had puzzled astronomers until the most recent discovery.

"Spitzer is helping to unravel secrets behind an object that has been imaged thousands of times," Sean Carey of NASA's Spitzer Science Center at the California Institute of Technology in Pasadena said in a press release. "It is intriguing Spitzer can read the fossil record of events that occurred billions of years ago within this beautiful and archetypal galaxy."


Image 1: The infrared vision of NASA's Spitzer Space Telescope has revealed that the Sombrero galaxy -- named after its appearance in visible light to a wide-brimmed hat -- is in fact two galaxies in one. Image credit: NASA/JPL-Caltech

Image 2: New observations from NASA's Spitzer Space Telescope reveal the Sombrero galaxy is not simply a regular flat disk galaxy of stars as previously believed, but a more round elliptical galaxy with a flat disk tucked inside.