It's smaller than an atom, but weighs like an asteroid.
Primary black holes could have been born in the first moments after the Big Bang and still remain one of the most unusual hypotheses of modern cosmology. The new work deals with almost absurd in appearance, but a physically acceptable question: what happens if the primary black hole passes through the human body. The answer turned out to be unpleasant, but calming: damage is possible, but the chance of encountering such an object is so small that in ordinary life it can be considered zero.
The primary black holes, or PBH, are different from black holes that form after the death of massive stars. They could occur in the early universe, when matter was compressed to huge densities. If in some areas the matter compacted strongly enough, gravity started the collapse and turned a small clot into a black hole. The mass of such objects could be very different.
Not all primary black holes could survive to this day. Lightweight objects should gradually lose mass through Hawking radiation: the quantum effect causes a black hole to emit particles and slowly evaporate. Objects are lighter than about a billion tons over the age of the universe would have disappeared. Taking into account other constraints, physicists often raise the lower estimate of up to 100 billion tons.
The mass of 100 billion tons is comparable to a small rocky asteroid with a diameter of several kilometers. But the primary black hole with such a mass would not be a giant celestial body, but an object much smaller than an atom. This is the strangeness of the scenario: the monstrous mass is concentrated in a microscopic volume, so the destructive action depends not only on the mass, but also on the distance and time of contact.
The gravitational field weakens rapidly with distance. At a kilometer, a person would not feel almost anything. A centimeter from the primary black hole, the attraction would be millions of times stronger than the earth, but the object would move too fast to pull matter for a long time. Typical velocity relative to the Earth is estimated at hundreds of kilometers per second, so it would pass through the planet in less than a minute.
For such a short span, the primary black hole would not have had time to absorb a noticeable volume of the rock. Much more important is the sharp gravitational disturbance along its path. The object would be carried through the bowels hundreds of times faster than the speed of sound in the rocks and would create a shock wave similar to a seismic push. Calculations for the mass of about a billion tons give an event about magnitude 4: people could feel trembling, but the global catastrophe is far away. An object of 100 billion tons would give a stronger signal, but the Earth would not destroy.
The work of 2025 postpones this calculation to the human body. The author assessed the energy of the shock wave, which the primary black hole would pass to the tissues, and used models close to the calculations of ballistic damage. The comparison is bleak, but understandable: you need to estimate how much energy will get into a small area of the body in an extremely short time and what kind of destruction will cause such momentum.
According to calculations, a noticeable injury begins at a weight of slightly above 100 billion tons. With a smaller mass, the shock wave is weaker. Direct contact with the substance of the body was also limited: due to the tiny size and huge speed, the primary black hole would affect only a small number of atoms.
Separately, the authors disassembled the tidal forces - the difference in gravitational influence on the close and distant areas of the tissue. It is such forces in more familiar scenarios that can stretch matter in a black hole. There is almost no time here: through the body the object would have flown about a microsecond. Therefore, the tidal effect would not be the main source of damage. For dangerous tissue destruction, this mechanism would require a mass of about 100 times more.
The trail after the flight would also not resemble a wide wound. The primary black hole would leave a submicroscopic canal because it itself is much smaller than an atom and does not have time to interact with a large amount of substance directly. The main danger would be created by the shock wave around the trajectory, and not the width of the track itself.
Such calculations are not necessary for the sake of a terrible plot. Primary black holes are seen as one of the possible candidates for the role of dark matter – a substance that does not emit light, but manifests itself through gravity and makes up a significant part of the mass of the universe. If part of dark matter really consists of PBH, the frequency of their encounters with Earth and people helps to test the permissible parameters of this hypothesis.
For humans, the estimate almost completely relieves anxiety: even with the most generous assumptions in favor of the primary black holes, getting into the body would be expected to be about once every billion billion years. The earth is larger, so the chance of meeting is higher, but for the planet the interval is estimated at about a billion years. If PBH constitutes a smaller proportion of dark matter or do not exist at all, the pauses between possible events become even longer.
Primary black holes could have been born in the first moments after the Big Bang and still remain one of the most unusual hypotheses of modern cosmology. The new work deals with almost absurd in appearance, but a physically acceptable question: what happens if the primary black hole passes through the human body. The answer turned out to be unpleasant, but calming: damage is possible, but the chance of encountering such an object is so small that in ordinary life it can be considered zero.
The primary black holes, or PBH, are different from black holes that form after the death of massive stars. They could occur in the early universe, when matter was compressed to huge densities. If in some areas the matter compacted strongly enough, gravity started the collapse and turned a small clot into a black hole. The mass of such objects could be very different.
Not all primary black holes could survive to this day. Lightweight objects should gradually lose mass through Hawking radiation: the quantum effect causes a black hole to emit particles and slowly evaporate. Objects are lighter than about a billion tons over the age of the universe would have disappeared. Taking into account other constraints, physicists often raise the lower estimate of up to 100 billion tons.
The mass of 100 billion tons is comparable to a small rocky asteroid with a diameter of several kilometers. But the primary black hole with such a mass would not be a giant celestial body, but an object much smaller than an atom. This is the strangeness of the scenario: the monstrous mass is concentrated in a microscopic volume, so the destructive action depends not only on the mass, but also on the distance and time of contact.
The gravitational field weakens rapidly with distance. At a kilometer, a person would not feel almost anything. A centimeter from the primary black hole, the attraction would be millions of times stronger than the earth, but the object would move too fast to pull matter for a long time. Typical velocity relative to the Earth is estimated at hundreds of kilometers per second, so it would pass through the planet in less than a minute.
For such a short span, the primary black hole would not have had time to absorb a noticeable volume of the rock. Much more important is the sharp gravitational disturbance along its path. The object would be carried through the bowels hundreds of times faster than the speed of sound in the rocks and would create a shock wave similar to a seismic push. Calculations for the mass of about a billion tons give an event about magnitude 4: people could feel trembling, but the global catastrophe is far away. An object of 100 billion tons would give a stronger signal, but the Earth would not destroy.
The work of 2025 postpones this calculation to the human body. The author assessed the energy of the shock wave, which the primary black hole would pass to the tissues, and used models close to the calculations of ballistic damage. The comparison is bleak, but understandable: you need to estimate how much energy will get into a small area of the body in an extremely short time and what kind of destruction will cause such momentum.
According to calculations, a noticeable injury begins at a weight of slightly above 100 billion tons. With a smaller mass, the shock wave is weaker. Direct contact with the substance of the body was also limited: due to the tiny size and huge speed, the primary black hole would affect only a small number of atoms.
Separately, the authors disassembled the tidal forces - the difference in gravitational influence on the close and distant areas of the tissue. It is such forces in more familiar scenarios that can stretch matter in a black hole. There is almost no time here: through the body the object would have flown about a microsecond. Therefore, the tidal effect would not be the main source of damage. For dangerous tissue destruction, this mechanism would require a mass of about 100 times more.
The trail after the flight would also not resemble a wide wound. The primary black hole would leave a submicroscopic canal because it itself is much smaller than an atom and does not have time to interact with a large amount of substance directly. The main danger would be created by the shock wave around the trajectory, and not the width of the track itself.
Such calculations are not necessary for the sake of a terrible plot. Primary black holes are seen as one of the possible candidates for the role of dark matter – a substance that does not emit light, but manifests itself through gravity and makes up a significant part of the mass of the universe. If part of dark matter really consists of PBH, the frequency of their encounters with Earth and people helps to test the permissible parameters of this hypothesis.
For humans, the estimate almost completely relieves anxiety: even with the most generous assumptions in favor of the primary black holes, getting into the body would be expected to be about once every billion billion years. The earth is larger, so the chance of meeting is higher, but for the planet the interval is estimated at about a billion years. If PBH constitutes a smaller proportion of dark matter or do not exist at all, the pauses between possible events become even longer.
