October 6, 2012
Milky Way Larger, Comprised Of More Dark Matter Than Previously Thought
redOrbit Staff & Wire Reports — Your Universe Online
The NAOJ team, led by associate professor Mareki Honma, used measurements from radio telescopes, including Japan's VLBI (Very Long Baseline Interferometry) Exploration of Radio Astrometry or VERA device, to determine that the distance from the sun to the center of the galaxy is 26,100 light-years, the observatory announced in an October 3 statement.
Honma's team also discovered that the galactic rotation velocity in the solar system is 240km per second, not 220 km per second as previously believed. As a result of these measurements, the Milky Way likely contains more dark matter than initially thought.
While scientists know that the Milky Way is a spiral galaxy, the NAOJ researchers point out that it is currently impossible to determine its exact size, shape and rotation velocity, due to our inability to observe it from afar. In order to see the entire galaxy's shape from within, they said, astronomers must measure the distance of each galactic object in order to compile a "galactic map" with an overhead perspective.
To do so, they must use what is known as trigonometric or annual parallax -- the difference in position of an object calculated while the earth revolves around the sun -- to accurately measure that object's position. Because the difference is minute, however, areas more than 1,000 light years away could not be accurately measured without the use of modern-day radio interferometers such as VERA.
Thus far, Honma's team has observed over 100 radio objects throughout the galaxy and has managed to chronicle the precise distances and motions of about 30 of them, the observatory explained. Combined with distance measurements and observations from other radio telescopes in the U.S. and Europe, they were able to analyze more than 50 total objects in drawing their conclusions regarding the size and rotation velocity of the galaxy.
"In general, galactic rotation velocity is determined by the balance with galactic gravity," the NAOJ said. "Therefore measuring galactic rotation is equal to measuring Galaxy´s mass. When the Milky Way´s mass within the solar system is measured with the latest Galactic rotation velocity from this research“¦ the amount should increase by no less than approximately 20%. It means that the total amount of dark matter in this area is larger than projected up until now."
"The current main theory of dark matter is that it consists of elementary particles. At the moment, some experimental particle physicists have been carrying out dark-matter detection experiments to directly detect dark matter. Our research findings also impact any experiments with for dark matter search," they continued, adding that their findings "emphasize again that the precise measurements of the Milky Way Galaxy promoted by VERA are effective to determine the structure of the Galaxy."