Calculations put a dark-matter-fed black hole's survival threshold at about 40 tonnes
A theoretical calculation finds that a miniature black hole of about 40 tonnes could grow without evaporating inside a white dwarf in a dense dark-matter environment. The threshold reflects the balance between mass lost through Hawking radiation and mass gained from the star and dark matter. Surviving old white dwarfs and millisecond pulsars may also constrain some ultraheavy dark-matter candidates; no black hole was detected.
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A threshold between Hawking loss and feeding
Chandrachur Chakraborty, H. A. Adarsha and Sudip Bhattacharyya calculated the lowest mass at which a miniature black hole could survive rather than evaporate inside a compact star. The black hole loses mass through Hawking radiation while gaining mass by swallowing surrounding stellar material and feeding on ultraheavy dark matter. In the theoretical study published in Physical Review D, the survival threshold for a white dwarf in the dark-matter-rich galactic bulge was about 40 tonnes.[1], [2]
The stellar setting changes the threshold
The calculation shows that the same threshold does not apply to every compact star. In a dark-matter-rich region, the value for a black hole inside a neutron star rises to about 600 tonnes. In a white dwarf in the galactic disk, where dark matter is thinner, about 10,000 tonnes is required. Without a continuing dark-matter supply, the critical mass grows further to about 10 to the power of 10 kilograms. These are survival limits under the model's assumptions, not masses of observed objects.[1]
Old stellar remnants constrain the candidates
The theoretical argument can also be used in reverse. White dwarfs about 10 billion years old and millisecond pulsars about 1 billion years old still survive. If certain forms of ultraheavy dark matter accumulated rapidly in their cores and formed destructive black holes, the continued existence of such old remnants would be difficult to explain. Their ages therefore place limits on dark-matter particle masses and how readily the particles collect inside stars. The study reports no detection of a new black hole or dark-matter particle.[1], [2]
