Three spiral galaxies are at the same distance from Earth and have similar characteristics. The disc of the first of them is observed “flat”, the second – at an angle of 45 ° to the line of sight, the third – from the “edge”. Which of these three galaxies can most accurately determine the relative mass contribution of dark matter?
A galaxy located at an angle of 45 ° to the line of sight will be the most convenient object for measuring the mass fraction of dark matter. The absorption of light from stars by dust will be small, and the stars themselves will have high radial velocities, which will make it possible to plot the rotation curve of the galaxy and determine its mass.
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