SEATTLE -- Tiny stars, a new way to search for planets outside our solar system, and a ring around the galaxy are among the out-of-this-world discoveries unveiled here this week at the annual meeting of the American Astronomical Society.
Scientists working at the Sloan Digital Sky Survey project discovered a ring of between 100 million and 500 million stars circling the Milky Way, about 180 quadrillion miles from Earth.
The ring of stars, 120,000 light years in diameter, is probably the remnant of a "dwarf galaxy" that was cannibalized by our own galaxy billions of years ago. That's the opinion of Heidi Newberg of Rensselaer Polytechnic Institute and Brian Yanny from the Fermi National Laboratory.
"It's an indication that at least part of our galaxy was formed by a lot of smaller or dwarf galaxies mixing together," said Newberg. The researchers say this is likely the largest of a series of star formations in the halo of the galaxy -- the area of space under the Milky Way's gravitational influence.
European space scientists discovered the same structure independently, confirming the ring's existence. But Roberto Ibata of the Observatoire de Strasbourg in France questioned the "cannibalization" theory. He said absorbing a smaller galaxy is one possible explanation; it's also possible that the ring could be a result of the Milky Way ejecting some stars during its own formation.
In other news of the cosmos, astronomers discussed two unexpected types of stars.
One is the smallest known "brown dwarf," a kind of star so small it doesn't shine because it has too little matter to start its nuclear furnace. Described by Frederick Vrba as the smallest brown dwarf identified to date, it is no bigger in diameter than the planet Jupiter -- about one-tenth the size of the sun, which is considered a medium-size star.
Vrba, who works with the U.S. Naval Observatory station in Flagstaff, Arizona, said the newfound star is only about one-half millionth as bright as the sun. He estimated its temperature at a mere 770 degrees Fahrenheit, about as hot as a pizza oven.
For decades astronomers have believed brown dwarf stars existed, but they are so small and dark that the first ones were not actually seen until the late 1990s. Since then researchers have discovered more than 250.
Vrba says the existence of stars as small and cool as this latest discovery raises questions about the distinction between stars and planets. Even at this size, he said, the smallest brown dwarf is certainly a star, since it is far brighter than Jupiter.
The details of another mysterious star with the same qualities as a brown dwarf were also revealed by astronomers.
The star, a newly discovered type, was found in a binary system known as EF Eridanus, around 300 light years from Earth according to Steve Howell of the University of California at Riverside and Thomas Harris of New Mexico State University at Las Cruces. It is a companion of a massive white dwarf that has collapsed from an ordinary star, and is being slowly eaten away by the gravitational pull of its neighbor.
Astronomers say they do not yet understand why the flow of matter to the white dwarf sometimes shuts down for a few weeks or months. In this case, the dark companion star stopped dropping material onto its white-hot companion in 1995.
In a separate announcement, a team at the Harvard-Smithsonian Center for Astrophysics reported they'd found a giant planet 30 times farther away from Earth than any other yet discovered. Astronomers were excited by the way the team, headed by Dimitar Sasselov, found the planet using a method theorized centuries ago but impossible to accomplish until now.
While most planets are detected by observing the gravitational wobble in a nearby star's rotation, astronomers discovered the new planet by observing the slight darkening when it passed between its star and Earth.
