Spitzer Finds Galaxy with Split Personality

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While some galaxies are rotund and others are slender disks like our spiral Milky Way,
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new observations from NASA’s Spitzer Space Telescope show that the Sombrero galaxy is both. The galaxy, which is a round elliptical galaxy with a thin disk embedded inside, is one of the first known to exhibit characteristics of the two different types. As said Dimitri Gadotti of the European Southern Observatory in Chile the Sombrero is more complex than previously thought. The only way to understand all they know about this galaxy is to think of it as two galaxies, one inside the other. The Sombrero galaxy, also known as NGC 4594, is located 28 million light-years away in the constellation Virgo. Spitzer captures a different view of the galaxy than visible-light telescopes. In visible views, the galaxy appears to be immersed in a glowing halo, which scientists had thought was relatively light and small. With Spitzer’s infrared vision, a different view emerges. Spitzer sees old stars through the dust and reveals the halo has the right size and mass to be a giant elliptical galaxy. While it is tempting to think the giant elliptical swallowed a spiral disk, astronomers say this is highly unlikely because that process would have destroyed the disk structure. Instead, one scenario they propose is that a giant elliptical galaxy was inundated with gas more than nine billion years ago. Early in the history of our universe, networks of gas clouds were common, and they sometimes fed growing galaxies, causing them to bulk up. The gas would have been pulled into the galaxy by gravity, falling into orbit around the center and spinning out into a flat disk. Stars would have formed from the gas in the disk.