Dark matter has had incredible explanatory power. After the introduction of the concept in the early 1980s, dark matter quickly became a central feature of our cosmological picture of the Universe. The current leading dark matter model is called Lambda Cold Dark Matter, or ΛCDM, and its predictions have consistently been borne out. A host of observational evidence confirms that our galaxy, as well as every other, sits within a halo (basically a spherical blob) of invisible, weakly or non-interacting matter, with a mass that far outweighs all the stars that sit within it.
There has been some skepticism, of course. Some have argued that there may be no dark matter and that instead, our understanding of gravity doesn’t apply on galactic scales, which could eliminate the discrepancies that we explain with dark matter. But as time goes on, the evidence that comes in continues to support dark matter. Those alternative models are still possible, but no convincing evidence has come to light in support of them.
But that doesn’t mean the ΛCDM model is perfect. Two problems have arisen in the form of predictions that don’t match certain observations. It may be the case that these issues can be solved by tweaking the model or by taking into account other processes that may be taking place involving normal, “baryonic” matter. A group of researchers has written a piece for the journal PNAS summarizing the various possible resolutions of the issues.
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