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Gaia data showing the motion of stars orbiting the center of the galaxy. Blue is the approaching star, and red is the group of stars moving away from us. (Source: ESA, Gaia, DPAC) |
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Stars are called stars because, unlike planets, they do not move as if they were fixed in the night sky. But it moves separately. But it is so far away that the movement is barely noticeable.
As a result of close observation over a long period of time, it was discovered that the stars are moving independently, though slowly, and are gradually changing their positions on the celestial sphere. Such a motion of a star is called a proper motion, and it is expressed as an angular velocity and is a value in a direction perpendicular to the gaze of an observer on the earth.
Stars, which are usually tens or hundreds of light-years away, appear to the human eye as if they are stuck in one place in the sky and do not move even after centuries of time, and thus the ancient constellations still maintain almost the same shape even today. For example, the shape of the Big Dipper in Ursa Major is almost the same as it did hundreds of years ago.
However, the stars in our galaxy are actually moving at a constant speed in outer space with respect to the solar system and the sun, and their proper motion occurs.
The natural motion of a star occurs in a random direction with respect to the observer, and the speed at which the star actually moves in space is called the space velocity. And the speed in the direction of the observer’s gaze is called the radial velocity.
If we know both the proper motion of a star and the value of its radial velocity, we can calculate the cosmic velocity at which a star moves with respect to the sun or galaxy.
Recently, data collected by the European Space Agency’s Gaia satellite’s all-sky survey shows the movement of the stars in 3D images.
A map composed of recent data taken by the Gaia satellite shows the motion of 26 million stars in the Milky Way. Stars marked in blue are moving towards us and stars in red are farther away. Lines depict the movement of stars across the sky.
The large blue area on the left side and the red area on the right side of the map give the impression that the stars rotate around the center of the Milky Way. The overall picture strangely resembles our Taegeuk pattern.
Understanding the details of stellar motion will help humans better understand the complex history of our galaxy and the origin of the sun.
Kwang-Sik Lee, Science Columnist joand999@naver.com
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