Our galaxy's 'halo' spinning in same way as its disk

Milky Way's halo is spinning and that too just like its disk, which contains our stars, planets, gas and dust, according to a team of astronomers.

The study from the University of Michigan's College of Literature, Science, and the Arts (LSA) sheds light on how individual atoms have assembled into stars, planets, and galaxies like our own, and what the future holds for these galaxies.

"This flies in the face of expectations," said Edmund Hodges-Kluck, assistant research scientist. "People just assumed that the disk of the Milky Way spins while this enormous reservoir of hot gas is stationary - but that is wrong. This hot gas reservoir is rotating as well, just not quite as fast as the disk."

The study focuses on our galaxy's hot gaseous halo, which is several times larger than the Milky Way disk and composed of ionized plasma.

Because motion produces a shift in the wavelength of light, the team measured such shifts around the sky using lines of very hot oxygen. They found that the galaxy's halo spins in the same direction as the disk of the Milky Way and at a similar speed - about 400,000 mph for the halo versus 540,000 mph for the disk.

"The rotation of the hot halo is an incredible clue to how the Milky Way formed," said Hodges-Kluck. "It tells us that this hot atmosphere is the original source of a lot of the matter in the disk."

"Now that we know about the rotation, theorists will begin to use this to learn how our Milky Way galaxy formed and its eventual destiny," noted Joel Bregman, adding: "We can use this discovery to learn so much more - the rotation of this hot halo will be a big topic of future X-ray spectrographs."

The study appears in the Astrophysical Journal.