Mass of Dark Matter Revealed by Precise Measurements of the Galaxy

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Mass of Dark Matter Revealed by Precise Measurements of the Galaxy |

A research team, led by Associate Professor Mareki Honma from the National Astronomical Observatory of Japan (NAOJ), has succeeded in precisely determining the astronomical yardstick for the Galaxy based upon the precise distance measurements with VERA from NAOJ and other advanced radio telescopes. The new findings are that the distance from the sun to the Galactic center is 26,100 light-years, and that the Galactic rotation velocity in the solar system is 240km/s.

The Galactic rotation velocity from this research is higher than that of previously known (220km/s). This results in the conclusion that the mass of the Galaxy, especially that of dark matter, is about 20% larger than what has been previously considered.

A research team, led by Associate Professor Mareki Honma（NAOJ) has reached the following two conclusions:

(1) The distance from the solar system to the galactic center is approximately 26,100 light years (*1);

(2) The galactic rotation velocity in the solar system (V０) (*2) is approximately 240km/s.

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=220km/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% larger than what has been considered so far.

VERA (VLBI Exploration of Radio Astrometry) (*3) 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 (*4) 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. continue reading