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What Would It Be Like to Fall into a Naked Singularity? [Guest Post]

The views expressed are those of the author and are not necessarily those of Scientific American.


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Last year, novelist Sergio De La Pava compared the American criminal justice system to the strange physics concept of naked singularities. That inspired me to ask the author of Sci Am’s article on the concept, theoretical physicist Pankaj Joshi of the Tata Institute of Fundamental Research in Mumbai (right in photo), for an update. Watch his lecture on YouTube, too.

Imagine a black hole without the “black” part. That is, imagine a black hole that you could fall into and, with effort, escape back out, as long as you didn’t hit the very center of the hole—its so-called spacetime singularity—and get crushed into oblivion. In other words, imagine a black hole without its outer perimeter (its so-called event horizon) but with its central singularity. That’s what physicists and cosmologists call a naked singularity.

It would be a strange beast, like a star so tiny you could hold it in your hand—although you would definitely not want to do that. The thing can have the mass of an entire star (or more) compressed into something approaching a mathematical point. Close to it, the energy densities, spacetime curvatures, and all other physical quantities would become arbitrarily large. Extreme physics would govern the happenings there. That is because both gravity and quantum effects come into their own near such a singularity, due to the extremely high spacetime curvatures and the super-high energy arising there.

Can naked singularities really form in nature, or does the collapse of a massive star always produce an event horizon? Roger Penrose (left in photo above) famously suggested that they cannot form. But later studies showed they do form under physically reasonable conditions, as I discussed in a Scientific American article several years ago. This is one of the most hotly debated frontier issues in modern black hole physics and relativistic astrophysics today.

Because Einstein’s theory of gravity allows for both black holes and naked singularities, it’s up to observers to settle the question. But how would a naked singularity distinguish itself from a clothed one? Singularities generally come in two types: those which are like events and others which are like objects. The big bang is an event-like singularity; a black hole is like an object. Both types can be produced as end state of gravitational collapse, depending on variables such as how fast or slow the collapse is, how the shells of matter fall in, and what the internal structure of the matter cloud is. A catastrophic collapse, such as a massive star imploding in matter of seconds, will produce an event-like naked singularity. A slower collapse could produce an object-like one.

When a naked singularity is event-like, it looks like an explosion. As the star collapses, it eventually rebounds because of quantum gravitational effects. In this case, observers need to look for an otherwise inexplicable outburst of energy.

When a naked singularity is objectlike, it looks rather like a black hole unclothed by a horizon (hence the name). A swirling disk of matter would form around it, and my colleagues and I recently showed that the disk would be much brighter than the equivalent around a black hole. It would also differentiate itself by its light spectrum, by the higher efficiency of particle collisions in its vicinity, and by the way it bends light.

Those of an adventurous frame of mind might imagine boarding a starship and plunging into a naked singularity. The descent would be rather different than the same trip into a black hole. For the black hole case, as kamikaze astronauts near the event horizon, the light they emit gets dimmer and dimmer, eventually going beyond any observable limit. In the naked singularity case, the light rays could escape from an arbitrary vicinity of the singularity. The astronauts would be able to remain in radio contact all the way down and send back direct pictures of quantum gravitational effects.

If you point a camera straight a black hole, you will see only inky blackness. If you point one at a naked singularity, you will see a small but bright object, albeit one with an unusual spectrum of light. Technically, you do not see the singularity itself, but its immediate environs. The astronauts would be able to say, “Ah, that’s how physics is unified,” and inform their friends back home of their achievement. They might even live to tell the tale.

Photo of Roger Penrose (left) and Pankaj Joshi (right) courtesy of H. Chauhan

George Musser About the Author: is a contributing editor at Scientific American. He focuses on space science and fundamental physics, ranging from particles to planets to parallel universes. He is the author of The Complete Idiot's Guide to String Theory. Musser has won numerous awards in his career, including the 2011 American Institute of Physics's Science Writing Award. Follow on Twitter @gmusser.

The views expressed are those of the author and are not necessarily those of Scientific American.





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  1. 1. jtdwyer 9:33 am 09/16/2013

    For the casual reader, this assertion would not be met with universal agreement.

    BTW – the correct link to the research report preprint is http://arxiv.org/abs/1304.7331.

    Link to this
  2. 2. Layer_8 4:33 pm 09/16/2013

    What happens with the speed of light? “Because Einstein’s theory of gravity allows for both black holes and naked singularities”. I doubt that strongly. If there are naked “singularities”, it must be an yet unknown quantum effect. And if it’s an quantum effect there is no singularity at all, thanks Heisenberg.

    My two cents

    Link to this
  3. 3. Cramer 7:21 pm 09/16/2013

    jtdwyer,
    What assertion? That naked singularities exist? Thanks for the link.

    Link to this
  4. 4. m 9:24 pm 09/16/2013

    No accretion disc, means the black hole could not form…

    It does not miraculously appear, except perhaps from the big bang, which cannot be proven so is just conjecture.

    However lets assume all matter exploded, and then reformed into among other black holes.

    The time dilation effects would ramp up as more and more mass became localised, until time almost stands-still at the black hole event horizon. But time doesn’t quite stand still completely.

    Therefore it would take a long time before a black-hole ate all its matter.

    Taking the big bang into context, its conceivable it took almost an eternity in that final form before it exploded.

    The compression of matter and time caused a paradox within the black-hole, that the only solution was an explosion. Essentially matter could keep compressing in definitely, however it violated the physical laws if it did and so the only option was a build up of “heat” (not heat in a traditional sense, maybe call it bheat), and then bang.

    In summary I don’t believe we will find naked black holes, where matter isn’t still falling into it after the horizon, which we can’t see through.

    Link to this
  5. 5. TonyTrenton 6:16 am 09/17/2013

    One of the fundamental characteristics inherited from the original singularity was rotational turbulence.

    Thus we get Event Horizons

    A naked singularity is an abomination. A very dangerous abomination.

    Link to this
  6. 6. joshi.divya2 7:52 am 09/18/2013

    Why only black hole or naked singularity. Can the collapsing star not settle to a stable non-singular object?

    Link to this
  7. 7. joshi.divya2 1:20 pm 09/18/2013

    Could it be a stable configuration which is outcome of collapse, rather than a black hole or a naked singularity?

    Link to this
  8. 8. christinaak 4:41 pm 09/19/2013

    It is highly probable that a quantum theory of gravity will make the existence of singularities impossible(naked or otherwise). It is also probable that black holes have a potentially measurable volume, structure (a quantized structure) and a finite density(albeit incredibly dense). Moreover, it is the universe’s black holes that contain information that determines the initial conditions for the universe at the onset of the next re-bang (within the context of an evolutionary cyclic model).

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