A huge gas cloud once considered a remnant from when the Milky Way or nearby galaxies formed is, in fact, a satellite of our galaxy, new radio telescope observations indicate. Unlike most satellites of the Milky Way, the body is orbiting in the direction opposite that of the galaxy's rotation.
The object, known as Complex H, is crashing through the outer parts of the galaxy, reports Felix J. Lockman of the National Radio Astronomy Observatory in Green Bank, W. Va., in the July 1 Astrophysical Journal Letters.
Previous studies of Complex H were limited because the cloud is passing behind the galaxy's outer disk, where gas and dust block visible light emitted by the cloud.
Astronomers had assumed the body was a so-called high-velocity cloud, a type of fast-moving mass of atomic hydrogen commonly found far from the galaxy. Such objects may ultimately be incorporated into the galaxy.