Magellanic Clouds And Dark Matter Warping The Milky Way

MILKY WAY

A still from the video shows how the Magellanic Clouds (yellow bead) produce the warp observed in the hydrogen gas layer of the Milky Way Galaxy, which is in the middle. The position of the sun is about half way out in the picture of the galaxy along the line marked X. The cross-hatched area represents the warped hydrogen layer at the present time. The looping line is the orbit of the Magellanic Clouds and the position of the bead on the line represents the location of the clouds at the present time. The orbital period is about 1.5 billion years. (Credit: Martin Weinberg/Leo Blitz).

Washington DC (SPX) Jan 10, 2006
After nearly 50 years, astronomers have figured out what causes the mysterious and periodic warping of the structure of the Milky Way galaxy: The Large and Small Magellanic Clouds are interacting with the galaxy's dark matter halo to magnify their gravitational influence, creating the warps as they orbit their parent in a cycle that takes about 1.5 billion years.

Using advanced computer models to infer the effects of stellar orbital velocities, astronomers at the University of California , Berkeley, and the University of Massachusetts, Amherst, have determined that the flattened disk of atomic hydrogen that permeates the entire galaxy is vibrating like a drum. Furthermore, this drum produces three distinct "notes" that would register some 64 octaves below middle C on the musical scale.

Though the galactic warp was discovered in 1957, its cause has remained unknown until now. "What is new is that this warp can be simply described," said UCB team leader Leo Blitz.

Dark matter is the key, Blitz explained to reporters at the American Astronomical Society's annual meeting. Scientists had long dismissed the clouds as potential causes of the warping, because their combined mass amounts to less than 2 percent of the Milky Way's. The new computer model includes the perturbations of the galaxy's massive dark matter halo caused by the motion of the Magellanic Clouds, which creates a wake that enhances their gravitational influence.

Though dark matter remains undiscovered via conventional observation, its effect on the gravitational dynamics of galaxies now is widely accepted. The Milky Way's dark matter halo, for example, is at least 20 times more massive than all of its visible, directly detectable matter. It remains the only explanation why the stars in the Milky Way's outer reaches orbit the galactic center far faster than they could if held in their orbits by the gravity of visible matter alone.

Blitz added that many other galaxies also seem to exhibit the same type of warping as the Milky Way. "It's very, very common," he said.

DARK MATTER

JHU-STScI Team Maps Dark Matter In Startling Detail

Baltimore MD (SPX) Dec 12, 2005
Clues revealed by the recently sharpened view of the Hubble Space Telescope have allowed astronomers to map the location of invisible "dark matter" in unprecedented detail in two very young galaxy clusters.