Researcher suggests that gravity can exist without mass, mitigating the need for hypothetical dark matter

Dark matter is a hypothetical form of matter that is implied by gravitational effects that can't be explained by general relativity unless more matter is present in the universe than can be seen. It remains virtually as mysterious as it was nearly a century ago when first suggested by Dutch astronomer Jan Oort in 1932 to explain the so-called "missing mass" necessary for things like galaxies to clump together.