How the Milky Way Formed
"The large area covered by Sloan and the accuracy of the multi-color observations allows us to revisit some of the classic questions in astronomy," said Yanny. "How did the Milky Way form? What does the galaxy look like as a whole?"
His team's hypothesis is that the ring may be the remains of a collision between the Milky Way and a smaller galaxy that happened billions of years ago. It's an indication that part of the Milky Way was formed by small galaxies joining together.
Astronomers believe that when small galaxies are pulled apart, the remains often form a stream of stars around larger galaxies.
Yanny and his colleagues estimate that this newly-discovered star belt is about 120,000 light years across. Gravity holds it in a circular orbit around the Milky Way.
"This ring is important because it lets us look at the motion of visible objects," Yanny says. "They give us clues to the nature of invisible dark matter pushing objects through space." Trying to understand the nature of dark matterand what exactly it isis the Holy Grail of astronomy.
Sloan is also revealing new space objects within the Milky Way itself. "We're finding a lot of stars in our own galaxy in the process," said Paula Szkody, an astronomer at the University of Washington in Seattle. Some of these are cataclysmic binary stars. These two-star systems are so named because they are no farther apart than the diameter of the sun, 864,000 miles (1.4 million kilometers).
"Many of them are close byonly 300 light-years awaybut they are so faint we just couldn't see them before," says Szkody. (One light-year is 5.8 trillion miles or 9.5 trillion kilometers, the distance light travels in a vacuum in a year.) "Now we are finding out what's really around us. Sloan allows us to see the total population of stars in our galaxy."
These paired binary stars are made up of a cool, low-gravity red dwarf star that loses mass to a hotter, high-gravity white dwarf star.
"The theory was that cannibalism (among stars) was quite common," Turner says. "Now we're starting to find them."
Sixty percent of the stars in the sky are binaries, but most are light-years apart and don't interact. Szkody estimates that the Milky Way contains more than 1 million close binaries. But astronomers have detailed information on only a couple of hundred of them.
Using the Sloan telescope, astronomers have discovered a few hundred close binaries and expect to find at least 400 by the end of the survey.
Sloan is expanding the horizons of space. "All of a sudden, questions you couldn't ask can be addressed," said Turner. "What this illustrates is what an explosive period of discovery we're in astronomy because of these new instruments."
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