black hole bares all for science

Two physicists ask if you could ever expose the mysterious core of a black hole in a new paper.

event horizon frame dragging
Computer simulation of a black hole’s event horizon exhibiting a phenomenon known as frame dragging, in which space is warped at different speeds based on the movement of the black hole

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.

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.

# science // astrophysics / black holes / event horizon


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