A previously unrecognized galaxy appears to be merging with the Milky Way, bringing hundreds of thousands of stars into our home galaxy that scientists had not noticed until now, astronomers said.
A survey of the northern sky has detected a huge, but diffuse structure within the confines of the Milky Way that does not seem to fit in with other parts of the galaxy that contains our solar system, scientists said Monday.
Robert Lupton of Princeton University told a meeting of the American Astronomical Society that the large but faint collection of stars rises almost perpendicular to the flat, spiral disk of the Milky Way. The most likely interpretation of the structure, the astronomer said, is that it is a dwarf galaxy that has been merging with our galaxy.
The dwarf galaxy lies in the direction of the constellation Virgo at an estimated distance of 30,000 light-years from Earth, researchers reported.
While some of the stars of the companion galaxy may have been observed with telescopes for centuries, they said, no one realized they belonged to another body because they are so close and commingled with Milky Way stars.
The Milky Way is a flat, pinwheel galaxy measuring more than 100,000 light-years across and containing an estimated 200 billion stars. A light-year is the distance light travels in a vacuum in a year's time, about 9.5 billion kilometers, or 5.9 trillion miles.
Astronomers found the merging galaxy through the Sloan Digital Sky Survey, a project that for more than five years has been mapping the distance and characteristics of millions of objects in space. The project is operated by a consortium of universities and other institutions.
The latest study, which has been submitted to The Astrophysical Journal for publication, shows that the Milky Way is still changing and evolving, said Mario Juric, a Princeton graduate student who is the principal author of the report. "It looks as though the Milky Way is still growing, by cannibalizing smaller galaxies that fall into it," he said in a statement.
Reporting at the same meeting, another group of researchers said they had an explanation for a mysterious warp in the disk of the Milky Way that has baffled scientists for decades.
Leo Blitz, a professor of astronomy at the University of California, and his colleagues Evan Levine and Carl Heiles charted the warp and found evidence that it is a ripple or vibration set up by two small galaxies that circle the Milky Way. These satellite galaxies, called the Magellanic Clouds, cause vibrations at certain frequencies as they pass though the edges of the Milky Way, the researchers said.
It was previously believed, Blitz said, that the Magellanic Clouds, with their combined mass being only 2 percent that of the Milky Way, were too small to influence their neighboring galaxy. But when the Milky Way's dark matter is taken into account, he said, the motion of the small galaxies can create a wake that influences the larger one.
Dark matter, invisible material that accounts for most of the universe's mass, is 20 times more massive in the Milky Way than all visible material, including stars. According to a computer model created with Martin Weinberg, an astronomy theorist at the University of Massachusetts at Amherst, dark matter spreading from the Milky Way disk with the gas layer can enhance the gravitational influence of the Magellanic Clouds as they pass through it.
Scientists Find A Galaxy Joining Ours
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