Astronomers at Swinburne University of Technology, Melbourne, have discovered an unusually shaped structure in two nearby disc galaxies. The Swinburne team recently developed new imaging software, making it possible to observe the double "peanut shell shape" formed by the distribution of stars bulging from the centers of these galaxies. The results are published in a new paper in Monthly Notices of the Royal Astronomical Society.
Using data from the Hubble Space Telescope and the Sloan Digital Sky Survey, the researchers realized that two of the galaxies they were studying (NGC 128 and NGC 2549) were quite exceptional. They are roughly 200 and 60 million light years away respectively, in the constellations of Pisces and Lynx, and they displayed a peanut shell configuration at two separate layers within the galaxies' three-dimensional distribution of stars.
"Ironically, these peanut-shaped structures are far from peanut-sized," says Swinburne's Professor Alister Graham, co-author of the research. "They consist of billions of stars typically spanning up to a quarter of the length of the galaxies."
Although the “bulges” of both galaxies were already known to display a single peanut shell pattern, astronomers had never before observed the fainter second structure in any galaxy.
"They resemble two peanut shells, with one neatly nested within the other; this is the first time such a phenomenon has been observed," says Bogdan Ciambur, the Ph.D. student who led the investigation.
"We expect the galaxies' surprising anatomy will provide us with a unique view into their pasts. Deciphering their history can tell us about transformations that galaxies like our own Milky Way might experience."