black hole bares all for science

August 10, 2009

Generally, when you think of a black hole, you probably imagine a pitch black sphere surrounded by a swirling accretion disk of white hot matter spinning around it. The pitch black “surface” of a black hole is the event horizon, a place where space and time are so distorted, there’s no way to avoid falling into a black hole. Think of it as taking a narrow, one way road between two towering cliffs. You’re going to follow the road because you have no other choice and eventually, you’ll hit a point where time and space break down; the singularity.

neutron collapse

However, two physicists at the University of Maryland think that there may be an instance in which a black hole doesn’t have an event horizon. Instead of following our metaphorical road, you could just fall into the bare singularity and its swirling vortices of energy without anything obscuring the view. The trick would be to find a rotating black hole which spins just a little bit below its maximum velocity and add a stream of matter flowing in the same direction as its spin to transfer the angular momentum. According to the formulas, that transfer of momentum should speed up the rotation of the black hole and over-spin it, breaking away the event horizon and revealing the singularity.

It would be impossible to do that with a rotating black hole spinning as fast around its axis as it can since the distortion of space and time in its ergosphere would be so intense, any stream of matter traveling with enough momentum would be caught up in the accretion disk and violently flung out. Why violently? Because a black hole spinning at its maximum speed could be making well over 1,000 revolutions per second. That’s more than 30% faster than the most dynamic neutron star on record. Of course if you found a slightly slower black hole and revved it up, would that really send it into overdrive and peel away the event horizon that shields the maelstrom within?

According to Roger Penrose’s Cosmic Censorship hypothesis, you just can’t have a naked singularity. You could be violating some fundamental laws of physics with these exposed anomalies which is why nature puts up an event horizon over this cosmic nudity. So far, the hypothesis seems to be holding and our observations of black holes aren’t yielding bizarre forms of radiation or anything else that lets us know that there might be a naked singularity on the loose. It’s still possible one could be out there but we haven’t detected it yet which is why cosmic censorship is still considered to be only a hypothesis.

But here’s the interesting bit about event horizons. They’re not a physical layer of matter. In fact, black holes contain no matter whatsoever. Whatever compounds the core of the stars from which they formed contained, were destroyed in the formation process and what’s left behind are vastly powerful gravitational ghosts which have mass only as a result of Einstein’s mass- energy equivalence. Hence, the event horizon around them is a mathematical boundary rather than a physical one. It doesn’t really shield a singularity as much as it marks the shift in the object’s tidal forces. Even if you could strip it away with very careful, precise and delicately balanced application of high energy physics, could it simply re-form an instant later or just refuse to disappear altogether?

Finally, there’s another challenge to Ted Jacobson’s and Thomas Sotiriou’s idea of black hole over-spinning and it has to do with the methodology of their paper. After using only classical physics, they warn that quantum phenomena inside and outside of a black hole could render any effort to strip away the event horizon pretty much impossible. Considering the immense complexity of the interactions between gravity, space, time and energy that happen in and around these enigmatic objects, ignoring even one potential effect makes this concept nothing more than a speculative mathematical exercise.

Share on FacebookTweet about this on TwitterShare on RedditShare on LinkedInShare on Google+Share on StumbleUpon
  • How can it be a black hole without an event horizon? If there isn’t an event horizon and light (information) is able to escape the gravitational pull of the object it can’t be a black hole can it?

  • “you need to be going faster than light to escape its pull.” And relativity flies right out the window? I’ve always pretty much seen the black hole as the “space” between the event horizon and the singularity. Maybe I’m wrong about this but I’ve always envisioned the way a black hole works as a ball rolling over the edge of a table. I as the viewer, my eyes level with the table top would see the ball fall off the edge of the table but would be unable to see the ball falling to the floor and the floor representing the singularity.

  • Would the “walls” of the structure be the distortion of space/time caused by the singularity and the currents flow within that? And while we’re discussing gravity I have a question for you, something that I’ve always wondered about and maybe you can answer for me (Are you starting to feel like the Science Guy?). Does gravity pull a falling object down to Earth or does the distortion of space caused by the Earth actually push the object down to towards the planet?

  • “How can it be a black hole without an event horizon?”

    This is basically the question on which the Cosmic Censorship hypothesis is based. Technically speaking, an event horizon isn’t a specific layer of the black hole’s structure per se. It’s an arbitrary point at which the tidal forces of the black hole are so strong, you need to be going faster than light to escape its pull. Those tidal forces are caused by the sudden change in the way the object deforms time and space around it as you get closer and closer.

    So technically there should always be an event horizon around anything as massive as a black hole because the swirling vortexes of energy which compose it would still exert enough force to pull objects into the singularity. After all, the deeper you go into a black hole, the more intense the gravity gets, eventually becoming practically infinite at the singularity. And on your way down, there will be a point at which escape velocity will have to exceed the speed of light, aka an event horizon.

  • “And relativity flies right out the window?”

    Absolutely not. That’s what makes a black hole what is it; you can’t go fast enough to escape its pull.

    “I’ve always pretty much seen the black hole as the ‘space’ between the event horizon and the singularity.”

    That’s actually not how a black hole works. It’s one structure which just happens to have two points we call the event horizon and the singularity. Between the two are torrents and swirls of energy which flow in bizarre currents according to current theoretical models of a black hole’s anatomy.

  • Thanks Greg.

  • The innards of a black hole are basically what remains of the matter from which it imploded being stirred by the tidal forces within the object. For rotating black holes the rate of its spin would also be an important factor.

    “Does gravity pull a falling object down to Earth or does the distortion of space caused by the Earth actually push the object down to towards the planet?”

    Your question is actually an interesting illustration of the difference between classic Newtonian gravitation and Einstein’s extensive updates to the theory. Newton knew that bigger objects pulled down smaller ones but he never really understood why that happened or how. And that’s what Einstein tried to figure out with his theory of general relativity.

    The answer is that both descriptions are right. Gravity pulls a falling object down to Earth and it does so because of the distortion of the space/time plane caused by the planet. Any object with mass makes a dimple in space/time and if you’re next to that dimple and aren’t moving fast enough to break away or have more mass than the object, that dimple will be like a slope leading to the object’s surface.

  • Marcelo Ballve

    Thanks for this Greg, I actually had just referenced black holes in something completely unrelated I wrote and I now see I had them completely wrong …