Can a primordial black hole collide with Earth?Although perhaps the appropriate verb is not “crash”, but “dive.”

Can a primordial black hole collide with Earth?
Although perhaps the appropriate verb is not “crash”, but “dive.”
At the beginning of the 20th century, it was observed that the equations of Einstein’s theory of General Relativity not only predicted that gravity is capable of bending the path of light, but also allowed the existence of objects so massive and dense that not even light can escape its gravitational field. These extreme objects would look like a dark disk, which is why they came to be called “black holes” in the 1960s.

Since then, the existence of black holes has been confirmed by the detection of stars orbiting very massive and “invisible” objects. In addition, the black holes that have been discovered to date suggest that there are two types: those that have a mass tens of times that of the Sun and are formed by the collapse of very massive stars and the supermassive black holes that reside in the center of galaxies, with millions or even billions of solar masses.

Now, what if the universe was full of much smaller black holes? What if one of these nearly undetectable objects collided with Earth?

Primordial objects
One of the most surprising astronomical discoveries of recent decades is the fact that the universe appears to contain much more matter than we can see both from the visible light it emits and from other wavelengths. All this invisible material has been called “dark matter” and several candidates have been proposed that could explain its true identity, such as large clouds of cold gas, new types of particles or flaws in the theory of general relativity.

One possibility is that the dark matter in galaxies is made up of large numbers of primordial black holes.

These black holes would have formed shortly after the Big Bang took place, when the energy density in some regions of the universe was so high that they collapsed under their own gravity. Although the smaller black holes that appeared around this time would have “evaporated” billions of years ago through the emission of Hawking radiation, some may have accumulated sufficient mass (on the order of at least billions of tons and diameters of less than a millimeter) to survive to the present day and be practically undetectable.
The existence of these primordial black holes is hypothetical at the moment, but if detected, should we be concerned about their possible impact with the Earth? That’s what the author of a new study has tried to find out.

Consequences for the Earth
A primordial black hole would not “hit” our planet like an asteroid does. Instead, it would traverse the Earth while attracting and absorbing material in its path. Before falling into the black hole, the absorbed material would swirl around the black hole and form an accretion disk, a cloud of incandescent material that releases a large amount of heat as it is engulfed at high speed. This phenomenon, together with the Earth’s gravitational field, would slow down the black hole as it passes through the Earth.

The result of the interaction between the two celestial bodies would depend on how much speed the primordial black hole lost during its passage through the interior of our planet. If the black hole were to slow down enough, it would be trapped inside the Earth and absorb the surrounding material until it consumes the entire planet. But if the black hole were moving at such a high speed that the Earth could not slow it down substantially, it would simply pass through the planet and back out into space on the opposite side. The only consequence for the Earth that this event would have is that the black hole would transmit part of its energy to our planet in the form of heat.
With this in mind, a new study attempted to estimate what is the probability that a primordial black hole (if it exists) will impact the Earth and consume it completely. And, luckily, their calculations indicate that it is practically nil, since the hypothetical primordial black holes that our galaxy could host would have to move so fast that, if they collided with the Earth, they would pass through it from one extreme to another, with minimal effects. on our planet.

Again: primordial black holes are hypothetical objects today. But, even if they did exist, the fact that Earth or any other planet in the solar system has been consumed by one of them in the 4.5 billion years that they have existed would indicate that the probability of collision is extremely low.