Recently there was an interest lecture by Joe Silk at Johns Hopkins University and the Institute of Astrophysics at Paris on the topic of the nature of dark matter. In a nutshell, the idea was put out that dark matter may take the form of black holes. Let us recall what all the fuss about dark matter is about.
The material that humans are made of, and that of the Earth and all that is on it, consists of protons and neutrons arranged into the form of atoms and molecules. This is called baryonic matter, and includes also the stuff that makes up the 100 billion stars in our galaxy, and all of the stars in the other 100 billion galaxies.
There is a considerable amount of baryonic matter out there. Somewhat surprisingly, it turns out that this baryonic matter sums up to a meager 3 percent of the total amount of matter in the universe. About 30 percent of the remaining matter is in a form called "dark matter." Note the other roughly 70 percent of the mass is in a form called "dark energy" which is not the topic of this post.
Focussing only on the dark matter for now, in addition to this dark matter not shining or interacting strongly with other matter, we humans are also very much in the dark about what it is.
There are searches for dark matter on different fronts, yet to date no one can pick up a piece of material, point to it and then make the billion dollar claim that this here is dark matter. To offer full disclosure, we are not entirely sure that dark matter even exists, or if it is just our lack of understanding of how gravity operates on large physical scales that leads us to believe it is there.
In any event, dark matter should be fairly all-pervasive, that is existing inside of our galaxy as well as outside of it. Yet experiments to detect dark matter that involve looking down into laboratories on Earth have failed to catch any elusive dark matter particles.
Well, what if dark matter instead takes the form of an inherently dark object, such as a black hole? Cosmologists generally agree that a large number of black holes could have been created early on in the universe's history, that is in addition to the black holes created by some massive stars.
With this in mind, perhaps we should also be looking up into space to search for the characteristically-dark black holes indirectly, which if the supposition is correct, may outnumber the stars.