It turns out that Andromeda, previously thought to be the biggest galaxy in this part of the universe, may not have bragging rights over the Milky Way after all.

Astronomers said Monday that the Milky Way is more massive than earlier known, given new measurements showing that the Sun is moving at 600,000 miles per hour around the center of the galaxy, or 100,000 m.p.h. faster than past calculations suggested.

The higher speed of the Sun means the galaxy must have more mass  about 50 percent more  so as to generate a stronger gravitational pull to keep hold of the Sun, as well as all its other stars. That expands the Milky Way to roughly the heft of Andromeda.

“We thought we were like a little sister of Andromeda,” said a member of the research team, Mark J. Reid, an astronomer at the Harvard-Smithsonian Center for Astrophysics. “Now we’re like fraternal twins.”