Expert: Philip Stahl - 9/9/2009

Question
QUESTION: HI, I've read that the laws of physics break down in a black hole, but specifically, what laws?  It appears time slows, it appears, mass bends space, what laws are violated?  Thanks

ANSWER: Hello,

The issue at hand is where, which regions of the black hole are subjected to examination of natural law consistency. The general consensus now is that at the center of the black hole is something called a "singularity" which is where all the problems reside.

The singularity is at a hole's very center and is unobservable. It is the point of ultimate breakdown of the natural laws we know, including conservation of mass-energy and the inverse square laws applicable to electric fields, and nuclear, gravitational forces. Why is this?

Because we are talking of a point with zero volume and infinite density. Even the combined phrase is impossible to comprehend.  

What you are talking about, in terms of time slowing, and deformation of space...is applicable to the region *outside the event horizon* of a hole. Close to it, but not *at* it. It does not apply to the singularity.

So the bottom line is in future when you hear or see references to "the laws of physics breaking down in a black hole" bear in mind which specific region it refers to. That is, the singularity.

Addendum: A "naked singularity" represents a singularity detached from the surrounding event horizon that usually is a part of normal black holes. Normally, the event horizon is what prevents light from escaping the black hole ...to enable direct observation. (Though there is a new device in the works, the Black Hole Imager, which will help to detect them more or less directly. For more, read the article 'Black Holes: Seeing the Unseeable' in ASTRONOMY, April 2007)

---------- FOLLOW-UP ----------

QUESTION: THank you for your response, its very informative and clear. I only have 2 follow up. If there is infinite density at the black hole's center jpw can it continue t consume anyting?  Also, question two, since mass controls, if a black hole were to meet an object with a larger mass (say a very large galaxy) would the galaxy absorb the black hole and what would that entail.  Thank you again for answering.

Answer
Yes, it can continue to consume....and consume..  Don't forget the existence of the singularity at the black hole's center drives the property of "consumption" and it is where all the consumed matter-mass ends up. Again, anything - like the gas from a stellar envelope- can be pulled through the event horizon by virtue of the powerful gravity - thence to end up in the black hole's center (singularity).


Re: the massive galaxy in relation to a stellar-sized (mass) hole, say 20 -30 solar masses), there is no problem in being aggregated gravitationally into the galaxy. In effect, the hole would be treated like an extremely massive star or object which then becomes a part of the galaxy. Of course, once appended, it would then begin to consume the surrounding dust, gas, debris etc.

Perhaps ultimately, a new supermassive black hole can form, analogous to those now theorized at the centers of most spiral galaxies.