Science1 distinct publisher3 min readPublished
A calculation of the race between accretion and Hawking radiation puts the smallest black hole that can grow inside a Galactic bulge white dwarf at about 40 metric tons, roughly 250,000 times below the no-feeding threshold.
The Scientist · Science desk
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Convert the units and the size of the effect is easy to read. The critical mass with dark matter feeding left out sits near 10^10 kg in representative compact stars [8], which is 10 million metric tons, against 40 metric tons for the most favourable case with feeding included [11]. The two thresholds differ by a factor of about 250,000 [17].
Where the star sits does much of that work. A white dwarf in the Galactic disk, where the solar system sits, needs an initial black hole of roughly 10,000 metric tons to grow rather than evaporate [10][7]; the same class of star in the bulge, which the phys.org account describes as much richer in dark matter, needs 40 [11]. Same star, factor of 250 [18]. A neutron star in the bulge comes out near 600 metric tons [12], fifteen times the white dwarf figure in the same region [19], and the account attributes the spread to the properties of the host star without breaking it down further [16].
Two pieces of the mechanism carry the result. The first is the word asymmetric. Because these hypothetical ultraheavy particles do not annihilate efficiently, they can pile up in the stellar core, become self-gravitating and collapse into what the account calls an endoparasitic black hole [3]; the accumulation step depends on that inefficiency, so the particle class is load-bearing rather than decorative.
The second is a regime problem most accretion calculations never face. At tens of tons the object is small enough that treating infalling matter as a continuous fluid breaks down, because an incoming particle's wavelength can be comparable to the black hole's characteristic scale, and absorption then has to be handled quantum mechanically; the fluid picture returns as the object grows [5]. The calculation follows both regimes at once, alongside stellar accretion, continued dark matter supply and Hawking loss [6]. The lowest thresholds sit precisely where the fluid approximation is least trustworthy, which is why I would want the quantum absorption step recalculated independently before treating 40 tons as firm.
The thing this does not tell you is anything about dark matter itself. Nothing has been observed; the calculated quantity is a positive growth rate under assumed conditions, whose endpoint is the host star being consumed and converted into a black hole [13][14]. Turning that into a bound would mean counting the compact stars in dark matter-rich regions that are still shining, and the phys.org account does not report that step [21].
What has moved is what a small black hole is allowed to weigh today. Hawking's 1974 result still says lighter holes evaporate faster [1], and the 10^12 kg figure still answers the question it was posed for, which is whether an isolated primordial black hole survives a cosmic age [2][9]. Inside a dense star being fed from two directions, that number was never the relevant one.
Ranked by verification strength, evidence, and original report placement.
In 1974 Stephen Hawking showed that black holes slowly lose energy through what is now called Hawking radiation, and that the lighter the black hole, the faster it evaporates.
A primordial black hole of mass around 10^12 kg has an evaporation timescale comparable to the age of the universe, so significantly lighter primordial black holes would not be expected to survive until today.
Neutron stars and white dwarfs can capture hypothetical ultraheavy asymmetric dark matter particles; because these particles do not annihilate efficiently they can accumulate at the stellar core, become self-gravitating and eventually collapse to form a tiny endoparasitic black hole.
Once formed inside a compact star, the black hole can gain mass by accreting ordinary matter from its host star and through the continued supply of dark matter, while Hawking radiation decreases its mass.
For an extremely small black hole the usual description of accreting matter as a continuous fluid can break down, because an incoming particle's wavelength can become comparable to the characteristic scale of the black hole, requiring a quantum description of particle absorption; the fluid-like accretion regime takes over as the black hole grows.
The calculation follows both accretion regimes while simultaneously accounting for stellar matter accretion, continued dark matter feeding and Hawking evaporation.
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1 article · September 5, 2026
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Evidence-backed comparisons of source perspectives and observed adoption signals. Read the methodology
Which Builder, Operator, and Investor concerns the observed source mix emphasized—not a truth score.
Evidence, demonstrated adoption, hype gap, incentives, and confidence are assessed independently, each on its own current evidence. How these are measured.
One peer-reviewed paper, described by its own author
Everything traces to a single Science X Dialog piece on Adarsha et al. in Physical Review D, which at least comes with a DOI and an arXiv preprint rather than a press release. Peer review puts a floor under the arithmetic, and the write-up is careful about what the 40 tons is: a growth threshold, not a detection. What is absent is anyone outside the author group testing the two-regime accretion treatment or the assumed bulge dark matter density that separates 40 tons from 10,000.
Nothing yet to count
There is no uptake to measure. The subject is a hypothetical dark matter particle inside stars nobody has surveyed for this purpose, and the reporting names no follow-up analysis, dataset, or observing campaign. Counting the journal publication as adoption would be dressing a paper up as a result.
Headline runs slightly ahead of the caveat
The phys.org headline says a 40-ton black hole 'can exist inside a star', and the loaded-semitruck comparison is built to travel; the calculation says only that such an object would have a positive growth rate given a bulge-like dark matter supply. The correction arrives in the same piece, unprompted, along with the warning not to read the in-star threshold as the primordial one. The overreach is in the framing, not in the physics being claimed.
Researcher writing up his own result
Science X Dialog exists so that researchers can present their published findings in their own words, and this piece does exactly that, with the author's affiliation appended at the foot. That is disclosure rather than concealment, and the caveats are handled more scrupulously than most science desks manage. Still, the editorial choices belong to a party with a stake in the finding: which threshold leads, which one gets the truck comparison, and the fact that no independent physicist appears anywhere in the story.
Standard physics, unseen assumptions
The scaffolding is safe: Hawking's 1974 mass dependence and the 10^12 kg primordial survival scale are textbook, and our arithmetic on the ratios between the quoted thresholds is checkable. The specific figures of 40, 600 and 10,000 metric tons depend on modelling choices this reporting does not expose, and there is no second account of them to compare against.