Dark matter mass in our galaxy '20% larger than projected'
Washington: The distance from the solar system to the galactic center is approximately 26,100 light-years, and the galactic rotation velocity in the solar system (V0) is approximately 240 km/s.
These are the two conclusions reached by a research team, led by Associate Professor Mareki Honma of National Astronomical Observatory of Japan.
These conclusions are drawn based upon the precise distances to celestial objects in the galaxy and their proper motions, a technical term to describe the stars'' change in position.
The International Astronomical Union has endorsed V0 = 220 km/s; this value was announced in 1986. When the V0 value derived from this research is applied, the mass of dark matter in the galaxy is about 20 percent larger than what has been considered so far.
VERA (VLBI Exploration of Radio Astrometry) and other VLBI arrays in the world were utilized to get most of the precise distances to about 50 objects and the data on their proper motions. At VERA, triangulation was used to precisely measure the distances to the objects and their proper motions.
The research team plans to further increase the number for objects of which they measure the precise distances and proper motions. In addition, the team has hopes to deepen understanding of the galaxy in which we all live by creating a 3D galaxy map, and then determine motions and mass distribution in the galaxy based upon the 3D map.
In general, galactic rotation velocity is determined by the balance with galactic gravity. 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 (Theta0 = 240 km/s), the amount should increase by no less than approximately 20 percent. It means that the total amount of dark matter in this area is larger than projected up until now.