An artist's rendering depicts the latest view of the Milky Way's structure, which scientists say rivals the Andromeda galaxy in scope.

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WASHINGTON — Take that, Andromeda! For decades, astronomers thought when it came to the major galaxies in Earth's cosmic neighborhood, our Milky Way was a weak sister to the larger Andromeda. Not anymore.

The Milky Way is considerably larger, bulkier and spinning faster than astronomers once thought — every bit Andromeda's equal.

Scientists mapped the Milky Way in a more detailed, three-dimensional way and found that it's 15 percent larger in breadth. More important, it's denser, with 50 percent more mass, which is like weight. The new findings were presented Monday at the American Astronomical Society's convention in Long Beach, Calif.

That difference means a lot, said study author Mark Reid of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass.

"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."

That's not necessarily good news. A bigger Milky Way means that it could be crashing violently into the neighboring Andromeda galaxy sooner than predicted — though still billions of years from now.

Reid and his colleagues used a large system of 10 radio telescope antennas to measure the brightest newborn stars in the galaxy at different times in Earth's orbit around the sun. They made a map of those stars, not just in the locations where they were first seen, but in the third dimension of time — something Reid said hasn't been done before.

Once the speed of the galaxy's spin was determined, complex formulas determined that the Milky Way, including invisible dark matter, is about 1 1/2 times the mass that astronomers had previously calculated.