Astronomers' record-breaking Milky Way measurement can help with galaxy mapping

A rendering of how the parallax technique works.    
   Image Bill Saxton NRAO  AUI  NSF Robert Hurt NASA

A rendering of how the parallax technique works. Image Bill Saxton NRAO AUI NSF Robert Hurt NASA

The most precise measurement yet of an object on the far side of the galaxy's centre is paving the way for a definitive map of the other side of the Milky Way.

"This means that, using the VLBA, we now can accurately map the whole extent of our galaxy", said Alberto Sanna, of the Max-Planck Institute for Radio Astronomy (MPIfR) in Germany. "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", Sanna said.

Using a 180-year-old technique and a continent-wide radio telescope system, scientists have directly measured the distance of a region all the way across from us at the other end of the Milky Way. Once the angle of position change has been noted, principles of trigonometry can be applied to measure the distance to the object in question. 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.

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As Milky Way is a spiral galaxy with many arms (one which has our solar system), it is hard to map its structure, shape without traveling hundreds of thousands of light-years outwards to see its face. You'll see your finger appear to shift with respect to background objects. Hence, parallax was one of the first tools used by astronomers that ultimately resulted in our modern picture of the universe.

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. That's because, the greater the distance, the smaller the observed shift. Over time, with advancing technologies, astronomers have been able to use parallax to directly measure greater and greater distances.

"These angles that are being measured are mind-boggling", says Dame. Also, star-forming regions are rich in water and methanol, both of which amplify the radio signals that VLBA detects, acting as natural masers. This effect makes the radio signals bright and readily observable with radio telescopes.

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Astronomers directly measured the distance to a region on the far side of our Milky Way Galaxy, past the Galaxy's center. We're looking all the way through the Milky Way, past its center, way out into the other side. However, the idea of measuring the distance to star-forming regions like this one could help with the process of mapping. This technique measures the apparent shift in the sky position of a celestial object as seen from opposite sides of the Earth's orbit around the Sun.

The astronomers said their goal is to reveal what our own galaxy looks like if we could leave it, travel outward perhaps a million light-years, and view it face-on, rather than along the plane of its disk. Thomas Dame at the Harvard-Smithsonian Center for Astrophysics in MA and his colleagues got around this by looking at a jet of radio waves that can outshine any emissions coming from that mess of stars.

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