January 6, 2009

Milky Way Spinning Faster Than Thought

Milky Way Bigger Than Once Thought

The Milky Way packs a big punch. In fact, scientists discovered that it is larger than Andromeda - not the little sister it was once thought to be.

Scientists mapped the Milky Way in a more detailed, three-dimensional way and found that it's bulkier and spinning faster than astronomers once thought.

The Milky Way is denser, with 50 percent more mass, and 15 percent larger in breadth.

The research was presented Monday at the American Astronomical Society's convention in Long Beach, Calif.

Study author Mark Reid of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts said the discovery was striking.

The slight 5-foot-5, 140-pound astrophysicist said the discovery is the cosmic equivalent of him suddenly bulking up to the size of a 6-foot-3, 210-pound NFL linebacker.

"Previously we thought Andromeda was dominant, and that we were the little sister of Andromeda," Reid said. "But now it's more like we're fraternal twins."

A bigger Milky Way means that it could crash violently into the neighboring Andromeda galaxy sooner than predicted - though still billions of years from now, said Reid.

Researchers used 10 radio telescope antennas to measure the brightest newborn stars in the galaxy at different times in Earth's orbit around the sun.

This time they mapped the stars, not just in the locations where they were first seen, but also in the third dimension of time.

The scientists used the National Science Foundation's Very Long Baseline Array (VLBA) radio telescope to remake the map of the Milky Way.

Experts say the VLBA's has an unparalleled ability to make extremely detailed images.

"The new VLBA observations of the Milky Way are producing highly-accurate direct measurements of distances and motions," said Karl Menten of the Max Planck Institute for Radio Astronomy in Germany, a member of the team.

"These measurements use the traditional surveyor's method of triangulation and do not depend on any assumptions based on other properties, such as brightness, unlike earlier studies."

Astronomers also say our Galaxy is rotating about 100,000 miles per hour faster than previously understood.

Our solar system is about 28,000 light-years from the Milky Way's center. At that distance, the new observations indicate, we're moving at about 600,000 miles per hour in our Galactic orbit, up from the previous estimate of 500,000 miles per hour.

The paper makes sense, but isn't the final word on the size of the Milky Way, said Mark Morris, an astrophysicist at the University of California Los Angeles.

Being bigger means the gravity between the Milky Way and Andromeda is stronger, and a long-forecast collision between the neighboring galaxies is likely to happen sooner.

But Reid said not to worry, that's still 2 to 3 billion years away.


Image 2: This artist's conception of the Milky Way shows the four-arm spiral structure confirmed by recent VLBA distance measurements (shown by green and blue dots). The data show that the Milky Way is spinning faster than previously believed. Our galaxy therefore is more massive than astronomers thought, matching Andromeda's heft. Red dots mark the galactic center and the location of our solar system. Credit: Robert Hurt, IPAC; Mark Reid, CfA, NRAO/AUI/NSF


On the Net: