A black hole as light as 40 tons can exist inside a star if dark matter helps

This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: In 1974, Stephen Hawking made a prediction that transformed our understanding of black holes. Black holes, he showed, are not truly black: They slowly lose energy through a quantum process now known as Hawking radiation.

The lighter the black hole, the faster it evaporates. For primordial black holes formed in the early universe, the implications are dramatic. A primordial black hole with a mass of around 1012 kg has an evaporation timescale comparable to the age of the universe.

Significantly lighter primordial black holes would therefore not be expected to survive until today. The tiny black holes considered here, however, need not have existed since the early universe. They can form much later inside compact stars.

Neutron stars and white dwarfs can capture hypothetical ultraheavy asymmetric dark matter particles. Because these particles do not efficiently annihilate, they can accumulate at the stellar core, become self-gravitating and eventually collapse to form a tiny endoparasitic black hole. Once formed, the black hole's fate is determined not by Hawking evaporation alone.

Surrounded by dense stellar matter, it can gain mass by accreting ordinary matter from its host star and through the continued supply of dark matter. Under favorable conditions, the calculations show that a black hole with an initial mass of only about 40 metric tons, roughly the mass of a loaded semitruck, can overcome Hawking evaporation and continue to grow. A newly formed endoparasitic black hole does not automatically consume its host star.

Its fate is decided by a competition: Accretion of stellar matter and continued dark matter feeding increase its mass, while Hawking radiation decreases it. There is also a quantum complication. For an extremely small black hole, the usual description of accreting matter as a continuous fluid can break down.