Relativity and Cosmology


Nature of Dark Matter

Authors: Amir Ali Tavajoh

Can we apply Kepler’s Laws to the motion of stars of a galaxy? Is it true that luminous matter contains the total galaxy’s mass? When we observe galaxies, we see interstellar gas, dust and stars which is called luminous matter. In 1922, a German astronomer, Jacobus Kapteyn was the first who suggested that dark matter exists. In 1933, A Bulgarian-American astronomer, Fritz Zwicky, explained the reason for existence of dark matter. He realized that gravitational lensing would provide the means for the most direct determination of the mass of very large galactic clusters of galaxies, including dark matter. [1]. Gravitational lensing is the consequence of Einstein’s general relativity. It was first observed in 1919, when an apparent angular shift of the Mercury close to the solar limb was measured during a solar eclipse and it was a strong proof for Einstein’s theory. Astronomers measure the total mass of a galaxy by Kepler’s laws (especially the law of periods) [2]. 〖 T〗^2=(4π^2)/GM a^3 (1) α: per Astronomical Unit M: per Solar Mass First of all, luminous matter is not equally distributed in galaxy because astronomers while evaluating the spectrums of stars of galaxy, found that stars of galaxy have different masses. Also based on Kepler’s law of areas, stars located closer to the center of black hole should have more orbital velocity than stars located further from center of galaxy but based on the Doppler Effect, when astronomers found out the orbital velocity of both stars by analyzing the absorption lines in spectrum of them, both were the same in orbital velocity [3]. We come to this conclusion that there should be a matter which is not luminous (because it doesn’t have any electromagnetic interaction) that let this phenomenon take place.

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[v1] 2017-01-28 06:44:22

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