Black Holes can't just be really dense objects can they?

Question

Sometimes I see people describe Black Holes as 'merely' an object whose gravity is such that light can't escape, i.e. very dense matter. As far as I know, neutronium, the stuff of a neutron star, is as dense as matter can get. To go beyond that you have to go beyond the known physical laws of the universe. It can't be normal matter, it really does have to be a 'hole' of sorts, leading 'somewhere else'. But how does this square with Hawking Radiation and the idea that black holes can 'evaporate'?

*nature_boy11*
-Yes, but Hawking radiation is the method by which the hole is supposed to lose 'mass'. Where is the mass?

Answer 1

They not only can, they are. And at the singularity that forms a black hole, the 'known physical laws' kinda break down. In fact, even neutrons break down into quarks (which pack far more densly) and the entirs thing is a kind of hyper-dense 'quantum foam' of raw quarks (or wave functions).

Doug

Answer 2

A singularity really isn't superdense matter; it's past that point. Matter simply cannot get that dense. What you have is a point at which the gravitational force is infinite. Recall that matter is energy - a singularity (the focal point of a black hole) is more like energy, not matter as we understand it.

As for being a hole - physically, the singularity would bend space-time, forming a "gravity well". The sun also forms a "gravity well" of sorts; light near tangent to the sun is bent inward due to the sun's mass. This is the effect you get for a black hole, but a black hole is in a much smaller area, and in the classical gravity equation,
F = G((m1+m2)/r^2),
where
F is the magnitude of the gravitational force between the two masses,
G is the gravitational constant,
m1 is the mass of the first point mass,
m2 is the mass of the second point mass,
and r is the distance between the gravitational centers of the masses,
r is much smaller for light tangent to a black hole, so the force is much greater. If you consider r to be extremely small, F approaches infinity, which is what is happening with a star collapsing into a black hole. However, there is a minimum mass necessary for a star to collapse completely into a black hole - this is called the Chandrasekhar limit (approximately 1.44 times the mass of Sol). This is apparent as the m1 term in the equation. m2 in this case is every particle in the star individually. However, since light has no mass, it would appear not to bend - that is where classical physics fails. General Relativity is needed to explain that.

Hawking radiation is fairly simple in contrast.
Modern theory provides for billions of complimentary particles and antiparticles spontaneously appearing from nowhere and disappearing again, so quickly and so frequently it's almost impossible to detect; these are called virtual particles. Very close to the event horizon of a black hole, these pairs generally annihilate regardless of the gravitational force, or are both sucked into the black hole. Occasionally, however, one particle is sucked into the black hole and the other escapes. The black hole thus loses energy as "radiation", since these particles must conserve energy.
This of course is a gross oversimplification, and I encourage further reading.

Answer 3

You're right, neutronium is as dense as matter can get. But gravity is non-linear, and so if you have too much neutronium in one place (about 1.4 times the mass of the Sun), even neutronium doesn't have enough pressure in the center to hold up the outer layers against gravity, and the whole ball will collapse into a singularity. (This is basically a description of one type of Supernova.) That's a Black Hole.

A black hole does not necessarily lead "somewhere else". All indications are that if you go in, you wind up squished in the center, and eventually your matter and energy are radiated away as Hawking Radiation.

You're also correct that the singularity predicted by General Relativity in this situation takes us beyond currently understood physics, specifically into the unknown realm of "Quantum Gravity". Hawking Radiation was the first well-identified and characterized Quantum Gravity effect.

Answer 4

The definition of a black hole is correct, "an object whose gravity is such that light can't escape." However, Neutronium is not the densest matter that can get. In terms of Atomic matter that is true, but in sub-atomic it is not. Neutrons are made of yet smaller particals. So, with enough force, the neutrons can be curshed into a smaller state. This physics is well understood and understood for a long time.

Well, the 'hole' part of your question is yet an other question because it involves never getting out again. Basically, the matter that falls in becomes trapped. Namely, if light can't get out then nothing will be able to get out. So, if matter falls in it will never come out; it's trapped forever.

Now, weard stuff happens in gravitional fields that strong; time looks like it runs slower to an outside observer. So, if matter falls into the hole then it will seem to us that it takes forever to fall into the hole. Again it becomes trapped by time as well.

Hawking points out that quatum effects happen at the very edge of the black hole. From Quntum physics we learn that virtual particals are always popping in to and out of existance. And any partical that is created has a counter partical. Namely, if an electron is made then an anti-electron is also made. So, at the edge of the black hole some of the time some of the particals will fall into the hole while the there partical will excape. So, to an outside observer, the hole can become a white hole, always emitting particals.

Also, we should realize that making particals takes energy and the energy comes from the gravitational field. So, as more particals are created and escape the more energy is taken from the field. Again, energy and mass are interchangable (E=mc^2). So, as the particals are emitted the lighter the hole becomes, or it appears to evaporates.

If the black hole is very tiny it will evaporate might be fast, but for holes that are large it can take longer than the life of the universe.

Answer 5

If a black hole could exist it would consist of 2 to 3 solar masses of matter squeezed into a volume of about 3 km in diameter.
The matter would be concentrated at the center in what they call a singularity.
The surface gravity would be such that the escape velocity would be greater than the speed of light.
Hawking radiation depends on the emergence of virtual particles that combine and annihilate each other except at the surface of a black hole where one would be trapped by the surface gravity and the other would escape to space and appear as radiation emanating from the surface and additionally reducing the mass of the entity.
You are right about the neutron star but the neutrons are separated from each other by one half the diameter of a neutron this would allow the density to increase if all the space was eliminated and no other reduction in size could occur.
A 2 to 3 solar mass neutron star could contract from 12 km in diameter to about 6 km and no additional increase in density could occur.
A black hole would have a diameter of about 3 km diameter.

Answer 6

In the black hole there is no space in the material in a black hole . As it collapsed the material in the star collapse got to the speed of light and according to the formula its mass is infinity. This gives a value for infinity . The gravity well is so great that the gravity may be 100 light years across. the simple gravity turners into a giant force.

Answer 7

Don't put too much faith into anything that Mr. Hawking says about black holes, they are just that extremely dense objects, more dense than a neutron star.

Answer 8

Black Holes, for the most part, are spinning, really dense objects -- yes they are.

Try not to let yourself be confused by the semantics of the phenomenon. The term, "black hole" refers to the appearance of "nothing" because the gravitational force of the Black Hole won't permit light to escape it.

While spinning, axial jets of gas form, ejecting matter and energy.

Answer 9

particular, a hollow is an extremely dense merchandise ;) each merchandise interior the universe with "mass" is a hollow in area... with very steep "factors". The earth is a hollow, the moon is a hollow, the solar is a large hollow... in case you stand too close to to the sting of the hollow, you will fall in.... and finally end up on the backside of the hollow. the hollow doesnt have any "factors" which you will carry to, on the thank you to get out of the hollow, you could desire to launch or advance up your self up and out of the hollow..... in case you DONT attain get away velocity, you fall flow into opposite the hollow.... a "black hollow" is largely a hollow whose gravity is SO stable, whose factors are so steep, whose intensity is so large, that no longer even mild has adequate velocity to flee it. Holes arent tunnels. there are no tunnels in area.

Answer 10

black holes is just like our bathtub.
if you pick the thing that blocks the water, the water is swirling..
in other words, a black hole is a dense but a powerful one..