Scientists have discovered the source of a galaxy’s two extra, ghostly spiral arms that show up only in some telescope images, cracking a 45-year-old mystery.
M106 (also known as NGC 4258), a stately spiral galaxy 23.5 million light-years away in the constellation Canes Venatici, appears in visible light images to have just two prominent arms emanating from its nucleus and spiraling outward.
“But in radio and X-ray images, two additional spiral arms dominate the picture, appearing as ghostly apparitions between the main arms,” said Andrew Wilson, part of a University of Maryland team of astronomers that used data from four space telescopes to arrive at an explanation of the strange phenomenon.
The “anomalous arms” consist mostly of regions of gas that are being violently heated by shock waves from a pair of jets of particles originating at the galaxy’s core, said Yuxuan Yang, who headed up the research, which will be detailed in the May 10 issue of the Astrophysical Journal.
In 2001, Wilson, Yang and Gerald Cecil of the University of North Carolina, Chapel Hill, noted that the jets are tipped 30 degrees with respect to the galaxy disk. If one could vertically project the jets down onto the disk, they would line up almost perfectly with the anomalous arms