A 40-Ton Black Hole Could Grow Inside a Star, Study Suggests

A black hole with roughly the mass of a loaded semitruck could, under specific conditions, grow inside a neutron star or white dwarf rather than disappear, according to calculations reported by Phys.org. The scenario begins with hypothetical ultraheavy asymmetric dark matter particles. A compact star could capture these particles, allowing them to accumulate at its core. Because the particles do not efficiently annihilate, they could eventually become self-gravitating and collapse into a tiny black hole inside the star. Such an object would face two competing processes. It could gain mass by absorbing ordinary stellar matter and by receiving additional dark matter, while losing mass through Hawking radiation. The smaller the black hole, the more rapidly Hawking radiation removes energy and mass. The researchers’ calculations included both the supply of matter from the star and continued dark matter feeding. They also accounted for a change in how matter is absorbed: for extremely small black holes, a conventional fluid description may fail and a quantum treatment of particle absorption is needed. The balance between growth and evaporation produces a critical initial mass. Below that threshold, the black hole shrinks; above it, incoming matter can exceed the mass lost through Hawking radiation. Without continued dark matter feeding, the characteristic threshold in representative compact-star cases could be around 10 billion kilograms. With dark matter included, the calculated threshold changes substantially depending on the environment. For a white dwarf in the Milky Way’s disk, the modeled critical mass is about 10,000 metric tons. In the more dark matter-rich Galactic bulge, it falls to approximately 40 metric tons. For a neutron star in the bulge, the corresponding figure is about 600 metric tons. The result does not indicate that a 40-ton black hole has been detected. It means that, under the conditions examined, such a black hole could have a positive growth rate instead of evaporating. Given enough time, the model says, it could grow until it consumed its host star, leaving a black hole. The study also uses the survival of very old white dwarfs and millisecond pulsars as a constraint on the possible properties and interactions of ultraheavy dark matter. The researchers note that rotation and magnetic fields could alter the result. Their findings were published in Physical Review D.