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What Is Dark Matter?
A simplified explanation is that most stars in spiral galaxies orbit the center of their galaxies at the same speed, regardless of their location. This is not the result astronomers expected to find. Newton's law of gravity says that objects farther from the center of mass should move more slowly, which is what astronomers see when they compare the inner planets to the outer planets in the solar system. However [link widoczny dla zalogowanych] in many spiral galaxies [link widoczny dla zalogowanych], the stars on the outer edges are moving as fast as those closer in to the center of the galaxy where most of the mass is seen.
Where Is the Dark Matter in the Milky Way?
In order for Newton's laws to be retained, a galaxy such as the Milky Way must have about 70 percent more mass than what astronomers see in the form of stars, gas, and dust. Just what this "dark matter" is has not yet been identified.
The astronomers observed a satellite galaxy, known as the Sagittarius Dwarf Galaxy, which has been shredded by its interactions with the much larger Milky Way. Observing the debris of this ripped-apart galaxy as it orbits the Milky Way has allowed the astronomers to use Newton's law of gravity to deduce where the dark matter must lie.
Scientists have recently determined that interactions between dark matter and visible matter in a galaxy is key to determining what shape a galaxy will have.
Dark matter is the term used to describe the missing matter that astronomers believe should be in the universe due to calculations of gravitational effects on many galaxies. Not all galaxies show evidence of "missing mass," but many of them do, including the Milky Way. In fact, one estimate puts the amount of dark matter versus visible matter in the universe at 95 percent.
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Evidence for Dark Matter Found
Rogue Black Holes
Common Space Acronyms
Milky Way Dark Matter Illustrations
They discovered that the dark matter lies in a halo that resembles a slightly flattened beach ball. This halo of invisible matter is triaxial, meaning that it has different axis lengths in all three dimensions. The squashed shape of the dark matter halo is roughly perpendicular to the disk of stars in the Milky Way. More studies of other satellite galaxies will help refine the data and determine the accuracy of the squashed beach ball model of dark matter distribution in the Milky Way.
New studies show that dark matter surrounds the Milky Way like a giant [link widoczny dla zalogowanych], slightly flattened beach ball.
The beachball illustration of dark matter shows the Milky Way's spiral arms with the approximate location of the sun indicated in yellow. The X, Y, and Z coordinates represent the triaxial shape. In the second illustration, the orange dots represent the location of the debris of the Sagittarius Dwarf Galaxy that has been torn apart by tidal interactions with the Milky Way.
Source: UCLA
Dr. David R. Law of the University of California at Los Angeles along with Dr. Steven Majewski of the University of Virginia and Dr. Kathryn Johnston of Columbia University have made the first ever three-dimensional map of where they believe the dark matter in the Milky Way is located.