If dark matter contains excess of primal black holes, then their gravitational lensing i.e. should be evident. Analysis of 740 known supernovas has shown that there is a strong upper limit of 40 percent of dark matter that can consist of black holes, and the black holes have none.
Built on a statistical analysis of 740 brightest supernovas known as of 2014, and the fact that none appear to be expanded or brightened by veiled black hole "gravitational lenses", the researchers at the University of California - Berkeley resolved that primitive black holes can make up roughly 40 percent of the dark matter in the universe.
Ancient black holes might only have been created inside the first milliseconds of the Big Bang, as regions of the universe with a concentrated mass, tens or hundreds of times that of the sun warped into objects a hundred kilometers across.
The results propose that none of the universe's dark matter consists of heavy black holes, or any related object, comprising massive compact halo objects (MACHOs).