Astronomers using the National Science Foundation’s Very Long Baseline Array (VLBA) have directly measured the distance to a star-forming region on the opposite side of our Milky Way Galaxy from the Sun.
Most of our Galaxy’s material, consisting principally of stars, gas, and dust, lies within a flattened disk, in which our Solar System is embedded. Because we can’t see our Galaxy face-on, its structure, including the shape of its spiral arms, can only be mapped by measuring distances to objects elsewhere in the Galaxy.
The astronomers used a technique called trigonometric parallax, first used in 1838 to measure the distance to a star. This effect can be demonstrated by holding a finger in front of one’s nose and alternately closing each eye — the finger appears to jump from side to side.
The VLBA, a continent-wide radio telescope system with ten dish antennas distributed across North America, Hawaii, and the Caribbean, can measure the minuscule angles associated with great distances. In this case, the measurement was roughly equal to the angular size of a baseball on the Moon.
Most of the stars and gas in our Galaxy are within this newly-measured distance from the Sun. With the VLBA, we now have the capability to measure enough distances to accurately trace the Galaxy’s spiral arms and learn their true shapes, Sana said.
The Milky Way has hundreds of such star-forming regions that include masers, so we have plenty of ‘mileposts’ to use for our mapping project, but this one is special.
Within the next 10 years, we should have a fairly complete picture, Mark Reid of the Harvard-Smithsonian Center for Astrophysics predicted.