Jean-Pierre Luminet in Inference Review:
Recent surveys make possible a precise estimation of the composition of the observable universe.7 Luminous matter represents only 0.5% of the total; dark energy, a form of non-material and antigravitational energy, 68%. The remaining 32% is attributed to dark matter—a contribution that is almost entirely invisible to telescopes.
The true nature of dark matter is one of the most significant challenges in modern astrophysics, especially since its distribution is far from uniform. Consider the galaxies Dragonfly 44 and NGC1052-DF2. Discovered in 2015, Dragonfly 44 has a mass comparable to the Milky Way, but appears to be almost exclusively dark matter (99.99%).8 By contrast, NGC1052-DF2, which was discovered in 2018, appears to be devoid of dark matter.9