Black holes arouse great interest among scientists and non-scientists, since the mystery that has been surrounded for years has provoked many speculations around them. However, it is becoming increasingly clear what they are, but are they all equal? Scientists have described four types of black holes: heavy weights, in the heart of galaxies and with mass of millions of stars; light weights or stars of great mass in the final phase of evolution; weight of feathers, sets of microscopic black holes formed after the Big Bang; and average weights. Although light weights have never been seen, they have been theoretically described and the average weights have recently been found two. They have a mass equivalent to 500 stars, but they are not greater than the Moon. Its history is yet to be clarified.