Researchers have discovered a phantom galaxy, all but invisible, circling our nearest galactic neighbor, the spiral-armed Andromeda. Astronomers found the galaxy, a ripped and torn mass of stars dubbed Andromeda VIII, by accident during observations of the much larger Andromeda galaxy.
“WE WERE BASICALLY looking at the outer regions of Andromeda to determine the galaxy’s velocity structure,” said Heather Morrison, lead author of the study and an astronomer at Case Western Reserve University.
But instead, Morrison and her team found a stream of stars along Andromeda’s outer fringe moving not only at a different speed of the rest of the galaxy, but in a different direction as well.
The stream turned out to be Andromeda VIII, a dim galaxy ripped apart by the tidal effects of the larger Andromeda’s gravity and strewn across 30,000 light-years. One light-year is about six trillion miles or 9.7 trillion kilometers. The smaller galaxy is only about half as bright as M32, Andromeda’s well-known companion, Morrison told SPACE.com.
Andromeda VIII is not just a dim, widely distributed object. It also sits directly in front of a bright patch of the prime Andromeda galaxy as seen from Earth, rendering it almost transparent to observers on the ground.
“We’re seeing it at a pretty early stage of destruction,” Morrison said. “If you follow it for another billion years, it will eventually all be absorbed by Andromeda.”
Morrison’s team used the 24-inch (about half a meter) Burrell Schmidt telescope at Case Western’s Warner and Swasey Observatory and the 11-foot (3.5-meter) telescope at the WIYN Observatory to study Andromeda VIII. Both observatories are located at Kitt Peak near Tucson, Arizona.
Case Western researchers Paul Harding and Denise Hurley-Keller, as well as George Jacoby of the WIYN Observatory also participated in the study. The results will appear in a fall issue of the Astrophysical Journal Letters.
Study of Andromeda VIII should help researchers increase understanding of the larger Andromeda’s gravitational influence, as well as the formation and ultimate demise of smaller galaxies. Andromeda, itself, is a spiral cousin to our own Milky Way, about 200,000 light-years across and two million light-years away.
Morrison’s team hopes future observations of Andromeda VIII will determine whether it once included a separate stream of faint stars originally discovered near the larger Andromeda galaxy in 2001.
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