Among the various classes of black holes (supermassive, stellar, intermediate mass …) there is one that is of particular concern to scientists. They are “primordial black holes”, much smaller in size (from microscopic to just a few km) but with masses that can be equivalent to that of a star. No one has ever seen one, but the theory says that such black holes should have formed in huge numbers during the first few seconds after the Big Bang.
And now two Spanish researchers, Juan García Bellido and Manuel Trashorras, together with Savvas Nesseris, all of them from the Autonomous University of Madrid, have discovered that these tiny and dark objects could continue to exist in the current Universe, traveling around the Universe in huge groups that are practically invisible. Your work just appeared on the ArXiv prepub server.
In the early Universe, just after the Big Bang, all existing matter was compressed into a fiery “particle soup” so dense that it could have collapsed at numerous points, giving rise to primordial black holes. If that multitude of millions and millions of small black holes have survived to the present day, they could have become even much smaller than they originally were, making them much more difficult to detect than “normal” black holes. that are formed as a consequence of the gravitational collapse of very large stars, and of course of the supermassive ones, that occupy vast regions in the centers of many galaxies.
García-Bellido and his colleagues carried out more than 5,000 computer simulations to try to find out how those supposed groups of primordial black holes could have evolved. In this way, they discovered that today there could be real “clouds” of them, each with a mass similar to that of the Sun and only a few km in diameter, extending over thousands of light years. The gravitational effects of cloud intermission, in addition, could cause some of them to be “expelled” from the group and launched into empty space at about 1,000 km per second.
Despite this, García-Bellido believes that there is no reason to worry: “The chances that one of these black holes expelled from some group could hit the Solar System in the short term are one in billions of billions.”
The scientists also found that both the groupings of black holes and those that, after being expelled, travel freely through the Universe should behave in much the same way as dark matter does, that mysterious form of matter that we cannot detect directly (since that it does not emit any radiation) and whose presence we can only infer by observing the gravitational effects it causes on nearby objects.
For García-Bellido, if primordial black holes are really “out there”, they could be the solution to the dark matter enigma, one of the biggest open questions in science in recent decades.