Emerging Technology from the arXiv

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Planets Could Orbit Singularities Inside Black Holes

The discovery of stable orbits inside certain kinds of black hole implies that planets and perhaps even life could survive inside these weird objects, says one cosmologist

  • April 11, 2011

It’s easy to imagine that black holes gobble up everything they encounter, consigning this stuff to eternal oblivion. Right?

Well, not quite. Today, Vyacheslav Dokuchaev at the Institute for Nuclear Research of the Russian Academy of Sciences in Moscow points out that certain black holes can have a complex internal structure. And that this structure ought to allow photons, particles and perhaps even planets to orbit the central singularity without ever getting sucked all the way in.

A black hole is a region of space where gravity is so strong that nothing can escape, not even light. However, cosmologists have known for some time that there are regions inside charged, rotating black holes where objects such as photons can survive in stable periodic orbits.

Dokuchaev’s contribution is to study these orbits in detail and to explore their dynamics. One of the problems that would at first seem to scupper any chance of planetary orbits inside a black hole is the way that the dimensions of space and time behave.

It’s well known that a traveller passing through a black hole’s event horizon arrives in a region in which the radial dimension becomes time-like, rather than space-like. Conventional orbits are clearly impossible here.

But travel further in and there is another horizon where the dimensions switch back again (at least, inside charged and rotating black holes). This is the inner Cauchy horizon and it’s beyond here that Dokuchaev says the interesting orbits for massive planets exist.

He calculates that the stable orbits are nonequatorial and have a rich structure (see picture above). They would also be brightly illuminated by the central singularity and by photons trapped in the same orbit.

That raises an interesting question: whether a planet in such an orbit could support a complex chemistry that is rich enough to allow life to evolve.

Dokuchaev clearly thinks so. “Advanced civilizations may live safely inside the supermassive BHs in the galactic nuclei without being visible from the outside,” he says, somewhat speculatively.

Of course, such a civilisation would have to cope with extraordinary conditions such as huge tidal forces and the huge energy density that builds up in these stable orbits as photons become trapped. There’s also the small problem of causality violations, which some cosmologists predict would plague this kind of tortured space-time.

Dokuchaev has taken an interesting idea and pushed it as far as he can. It’s one I suspect readers can have a lot of fun with too.

Ref: arxiv.org/abs/1103.6140: Is There Life Inside Black Holes

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