Science1 publisher2 min readPublished
Theorists calculate that primordial black holes in a micron-wide extra dimension end up five-dimensional
Luis Anchordoqui's Lehman College team calculates that primordial black holes in a universe with a micron-wide hidden dimension would end up five-dimensional. The work links a proposed dark matter candidate to an extra dimension that has no more evidence behind it.
The Scientist · Science desk
Drafted by a language model from the sources cited here and checked against its claim ledger before publication. How we use AISend a correction
What happened
- In the dark dimension scenario, ordinary matter and forces stay confined to familiar space, while gravity alone can spread into the hidden extra dimension.
- The authors report that black holes formed from cosmic strings could have lifetimes comparable to the age of the universe.
- The result comes from applying proposed rules of quantum gravity in theoretical calculation, with no observations involved.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- constraint If the dark dimension exists, models that treat small primordial black holes as ordinary four-dimensional objects would misdescribe them from formation onward.
- constraint The lifetime figure is the part that touches dark matter, but a lifetime comparable to the universe's age does not show these objects survive today in useful numbers.
- capability If either idea is ever confirmed, phys.org's account says such black holes could carry details of high-energy physics in the early universe.
The calculation turns on size. Primordial black holes can be extremely small. In a universe where gravity alone can reach a hidden extra dimension, that smallness could change how they form and how long they last, according to phys.org's account [8]. The authors set out the problem directly. "In this paper, we revisit the formation mechanisms of PBHs and ask whether, within the dark dimension scenario, PBHs are effectively 4D or 5D black holes," they wrote [5].
Both ingredients are hypothetical. No primordial black hole is known to exist. If they do exist, they would have formed in the early universe instead of from dying stars, and they may make up dark matter [2]. The dark dimension is also a theoretical construct [3].
There is no experiment here in the usual sense. The paper, titled "Primordial black holes are five dimensional," appeared in Physical Review D [1]. The team worked through theoretical math and physics, applying proposed rules of quantum gravity to black holes in the dark-dimension setting [4]. The nearest thing to a control is the comparison built into the question: the same object treated as four-dimensional and as five-dimensional. The answer depends on how the black hole was made. Some start out behaving like standard four-dimensional objects, then become unstable and turn five-dimensional. Those formed from cosmic strings skip the four-dimensional stage altogether [6].
I think the lifetime result is the part that bears on dark matter, because a candidate has to exist today to count. The authors wrote that black holes formed from cosmic strings "can have lifetimes comparable to the age of the universe" [7]. Comparable is a weaker word than longer. The published coverage does not say how many such objects would remain now, what masses they would have, or what signal a telescope or detector could look for.
That gap matters for any claim that the paper hands observers something to test. On the evidence available, it supplies a set of conditional statements: if the dark dimension exists and if primordial black holes formed, this is what they would be. Paul Arnold, writing for phys.org, said the research "connects two mysteries into one bigger one" and "still leaves us waiting for real-world proof" [9]. He added that "if either is real, it could give us details about the high-energy physics of the early universe" [10].
What to watch
- A follow-up that turns the cosmic-string lifetime result into a specific predicted signal that astronomers could search for.
- Estimates of how many cosmic-string black holes would remain at the present day, and at what masses, since a dark matter role depends on both.
- Any independent evidence for or against the dark dimension itself, because every result in the paper is conditional on it.