We residents of the Milky Way can puff ourselves up with pride: A new study has discovered that our galaxy is more of a force to be reckoned with than previously realized. 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 [The New York Times].
The new calculation puts our galaxy’s mass about equal to that of the nearby Andromeda galaxy, which was previously thought to be bigger than the Milky Way, says lead researcher Mark Reid. “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” [AP]. But although the estimate gives our galaxy some new bragging rights, it’s not all good news. Being bigger means the gravity between the Milky Way and Andromeda is stronger. So the long-forecast collision between the neighboring galaxies is likely to happen sooner and less likely to be a glancing blow, Reid said [AP]. Luckily, that collision still isn’t expected for 2 to 3 billion years.
The make their discovery, announced at the ongoing American Astronomical Society meeting, researchers used the Very Long Baseline Array, a combination of 10 radio telescopes stretching from Hawaii to the Virgin Islands. Researchers used the radio waves that effectively penetrate clouds of interstellar gas to examine bright star forming regions around the galaxy when the sun was at different places in its orbit. “We’re using trigonometric parallax. It’s essentially what surveyors do here on Earth,” [Reid] said. “If you know the length of one leg of the triangle and the angles between the legs, you can calculate all the lengths.” In this case, they make an observation of the same region at two different times of the year, creating a triangle out of the earth’s two positions and the star itself [Wired News]. Then they could determine the speed at which our sun is moving, and then the mass of the galaxy.
It’s difficult to get an accurate idea of the Milky Way’s appearance from our position within it, but the researchers say their measurements do add evidence to the picture of a galaxy with four spiral arms in total, two of which are “minor” arms that contain only newborn stars. Most star formation in our galaxy takes place in the Milky Way’s spiral arms — where gas is compressed, triggering the birth of stars. By measuring the distances to [star formation regions] that appeared to reside within the same spiral arm, the researchers were able to determine how tightly wound each spiral arm is and how many times it wraps around the Milky Way [Science News].
80beats: Confirmed: Monstrous Black Hole Lurks in Our Galaxy’s Center
80beats: A Better Portrait of Our Milky Way