Most matter in the Universe is in a “dark matter” form that has only been observed through its gravitational interaction. How warm is this dark matter? A new constraint has become available thanks to the observations of the line-of-sight velocities of individual stars in dwarf spheroidal galaxies dSph, which allow a measurement of the dark matter density
. From the measured
of 27 dwarf spheroidal galaxies dSph, we obtain an estimate of the comoving thermal velocity and mass of the dark matter particles.
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