What Is The Probability And Consequences Of Collision Of Primordial Black Holes With Earth? (Cosmology)

Sohrab Rahvar investigated the scenario of collision of primordial black holes (PBHs) with earth. He showed that this collision has different consequences as heating the interior of the earth through dynamical friction and accretion processes. The findings of this study recently appeared in Arxiv.

Primordial black holes are a hypothetical type of black hole that formed soon after the Big Bang. In the early universe, high densities and heterogeneous conditions could have led sufficiently dense regions to undergo gravitational collapse, forming black holes. They are plausible candidates of dark matter.

Now, by assuming that PBHs fill the dark content of the Milky Way Galaxy in the Galactic halo and dark disk, Sohrab Rahvar calculated the probability of collision of the PBHs with Earth. He showed that the black holes with the mass M < 1015 gr have the chance of more than one impact per billion years with Earth and the rate of black holes that could be trapped in the interior of the earth is almost zero. But, how can we say so confidently that, there are no primordial black holes trapped inside the earth?

“Well, since the velocity of black holes in the halo and the dark disk is high, the dissipation process inside the earth is not effective to decelerate the black holes and black holes do not sink inside the earth where in this case black holes could heat the interior of the earth and finally swallow the whole mass of earth. The number of this event for M ≃ 1015 gr is about 10¯11 Gyr¯1. This calculation assures that probability of primordial black holes being trapped inside the earth is almost zero.”

Another important point to be noted is that, those black holes that cross the earth, heat the interior of the earth through various mechanisms like through dynamical friction which can generate heat in the range of 105–108 J and through accretion process by about 1015 J.

Moreover, he calculated the energy released by a black hole collision with earth and compared it with the impact of asteroids on the earth. He have shown that the accretion process by the black holes is the dominant process for energy release. The amount of energy from this collision is comparable with a kilometer size asteroid where it happens four orders of magnitude more frequently than a black hole collision.

Finally, he concluded that the likelihood of the dangerous impact of primordial black holes with the earth is very low.


Reference: Sohrab Rahvar, “Possibility of Primordial black holes Collision with Earth and the Consequences”, Arxiv, pp. 1-5, 2021.
arXiv:2107.11139


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