Take the 2-minute tour ×
Physics Stack Exchange is a question and answer site for active researchers, academics and students of physics. It's 100% free, no registration required.

Non-astrophysicist visitors to Black Hole, will most likely barely make it past the introduction before getting lost in the technical details. Moreover, the Wikipedia article does not teach laypeople how to think of a black hole, or give them a better intuitive sense than pop culture references to black holes, some of which are really awful!* So, please explain the concept of a black hole in a way that won't glaze over the eyes of your typical English or Business major.

*For examples, and the pop-culture smearing of the concept of black hole together with other gravitational anomalies, see:

share|improve this question
add comment

5 Answers

Personally I'm not entirely sure how much technical detail you require, only in a generally digestible fashion. However, given that I have recently read answers provided to numerous questions regarding black holes*, formulated for the 'general reader' but by someone who, to drastically understate, certainly knows much, much more than myself, I'll quote:

A black hole is an incredibly dense celestial object containing so much mass it has generated a powerful gravitational field from which not even light can escape. Anything that falls into a black hole will be crushed out of existence.

Black holes are spherical and expected to be spinning, dragging the spacetime continuum like honey around a spinning spoon. In these confused regions of spacetime, it won't be clear whether you're travelling through time or space or both.

Just like any object that hits the black hole, light too will be swallowed completely and quite possibly forever. Light that misses the black hole, but passes very close to it will be deflected onto a new course through space.

Nothing, not even information is expected to be able to escape from a black hole. This s contentious because if, as Stephen Hawking suggests, black holes eventually evaporate and die, they must be radiating particles. In turn, it should be possible to detect and measure these particles, but currently none of our telescopes are able to get any readings when pointed at a black hole - these areas are void of any information. So, to resolve this contradiction , it's suggested even information is sucked into the heart of the black hole.

We don't know what happens at the centre of a black hole. Our current theories break down because they can't deal with infinitely dense objects. So, physicists are trying to develop new theories of gravity to answer what lies at the bottom and whether they lead anywhere. Called a singularity, one is thought to exist at the centre of every black hole.

This may be far less technical than you desire - let us know if so. Though, even so it is an easy read with enough of an idea and general knowledge to be contributed, I believe.

*Source: BBC Focus, Brian Cox, April 2011

share|improve this answer
add comment

The answer really depends on how much detail you want. But for a basic answer this is what I tell people:

A black hole is simply a region of space from which no light or information can escape. The reason for this is that the density of matter in that region has become so high that the escape velocity, the speed needed to get out, is larger than the speed of light and since nothing can travel faster than the speed of light, nothing can escape.

The point where the escape velocity is equal to the speed of light around a black hole is known as the event horizion. The distance from the center of the black hole to the event horizion determines its size. Black holes are small. A solar mass black hole is only about 3 km in radius and that diameter scales linearly with mass.

Black holes are not cosmic vacuum cleaners that "suck" everything nearby into it. It behaves just like any other massive object. If you were to suddenly replace the Sun with a black hole of the same mass, the only thing that would happen on Earth is that it would get really dark and cold. It would not effect the orbit at all. If you got in really, really close, there are some weird effects but you would most likely be ripped apart by tidal forces long before you got there to measure them.

At that point I answer any additional questions that might come up.

share|improve this answer
add comment

Both above answers are well worded, succinct, and not terribly confusing. But sometimes you have go one step further into simplicity.

Imagine the fattest person you possibly can, like Bender when he became Human. Surround this person with a gigantic buffet. What happens next is kinda like a black hole, except change the buffet for all matter and energy, and the fat person with a teeny weeny rip in the very fabric of space and time.

Now, this explanation bypasses quite a bit about black holes, but for some people this may be the best answer for them. Hopefully they will ask questions after, so you can more fully explain black holes.

I find that when answering scientific questions (I should point out right about now that I am merely an enthusiastic layman), it's best to understand the person who is asking the question, and answering any followup questions. You have to find the best description for that person/audience. In short, there will never be a 'one size fits all' answer for any scientific question. You have to see from the perspective of the person asking the question in order to best answer that question.

share|improve this answer
add comment

I would avoid the use of the term 'singularity' and keep it short and crisp: "Any region containing a mass $M$ is believed to be a black hole, if we can rotate around it a circular hoop with circumference $L$ such that the ratio $L/M$ equals $9.331 10^{-27} m/kg$."

The explanation could then continue with the usual remarks:

"Black holes combine some remarkable properties. Most notably, the region circumscribed by the hoop is in a way disconnected from the universe outside. All an outside observer can learn about the region 'inside the hoop', is the mass, the angular momentum and the electrical charge it contains. No other information can leak out. Note that while the mass/circumference ratio ($M/L$) is prescribed, the mass density ($M/L^3$) can attain any value. Small black holes are incredible dense, very large black holes can be less dense than earth's atmosphere."

share|improve this answer
add comment

Here's my shot without appealing to concepts that are unique to math or physics.

Newton discovered that the strength of gravity of an object gets bigger as the object gets more massive and bigger as your distance to the object gets smaller.

Now, light isn't infinitely "strong"/fast -- it has a limit. Even the fastest runner can't run up a hill if the hill is steep enough ... against a river if the river is strong enough ... or away from a rope if the rope is tight enough.

Imagine light running away from an object with gravity. Now make the mass bigger and bigger ... or the distance to the light smaller and smaller. Because light isn't infinitely "strong", there has to be a point where the gravity gets strong enough -- the hill gets steep enough, the river gets strong enough, the rope gets tight enough -- that light reaches that point where it just "gives up". Like a runner running against a river that's getting faster and faster, there's a point where the river just gets too fast.

At that point -- that too-steep, too-strong, too-tight point -- that object becomes a black hole.

And well, because light is the fastest thing there is ... if light can't outrun a black hole, nothing can.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.