October 23rd, 2012 by James Ayre
Large galaxies are usually categorized either as pinwheel-shaped spiral galaxies or blobby elliptical galaxies. The Milky Way is a pretty typical spiral galaxy, with lots of gas and dust giving birth to new stars. While ellipticals are more like the “cosmic retirement villages, full of aging residents in the form of red giant stars,” notes the Harvard-Smithsonian Center For Astrophysics.
Now, in something of a surprise discovery, researchers have found that one elliptical galaxy that has been extensively studied, Centaurus A, is actually harboring a gassy spiral at its core. It has a split personality.
“No other elliptical galaxy is known to have spiral arms,” said lead author Daniel Espada (National Astronomical Observatory of Japan & Harvard-Smithsonian Center for Astrophysics). “Centaurus A may be an old galaxy, but it’s still very young at heart.”
But Centaurus A isn’t really a typical elliptical for other reasons anyway. The presence of a dark dust lane through its middle is one feature that really stands out as unusual. It’s thought to be a sign that it consumed a spiral galaxy around 300 million years ago.
“Centaurus A slurped that galaxy’s gases down, forming a disk that we see nearly edge on. From our point of view, any features in that disk have been hidden by the intervening dust.”
In order to visualize the disk’s structure, the researchers used the powerful Submillimeter Array at the Smithsonian, making it possible to see through the dust, picking up signals from carbon monoxide gas. Then by mapping these signals out the researchers were able to create the image of two very distinct spiral arms in the galaxy’s center.
The spiral arms are of very similar sizes and shapes to the ones in galaxies like ours. And just like in the Milky Way, these spiral arms are still forming new stars.
“Centaurus A has been given a new lease on life by that past merger,” said Espada.
Computer models seem to suggest that these spiral features will endure for at least a few hundred million more years.
“Although Centaurus A is the first elliptical galaxy found to have spiral arms, it may not be the last. Since it’s only 12 million light-years away, it’s relatively nearby and easy to study. The Atacama Large Millimeter/submillimeter Array (ALMA) potentially can find more split-personality galaxies with its improved radio vision.”
“We definitely will use ALMA to search for other objects that are similar to Centaurus A,” added Espada.
The research was just published in The Astrophysical Journal Letters.
Image Credits: ESO
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