Black Holes: Overweight Neutron Stars?

[PlutonianEmpire]

Every now and then, I speculate, could a black hole really just be a really heavy neutron star? I figure that since the same process that forms black holes also form neutron stars, that both would consist of roughly the same materials.

Could this assumption be correct?

[Fenerit]

"material", for a black hole doesn't make sense.

[julesstoop]

A theoretical sufficiently large neutron star could have an event horizon (how such an object could form is a different question altogether). But that alone black hole it doesn't entirely make. Besides having an event horizon, a true black hole is supposed to be a singularity.

[Hungry4info]

Actually, I agree with PlutonianEmpire.

As I understand it, a black hole is just any object with an event horizon. The more massive the neutron star, the greater the surface escape velocity. Make it massive enough, and the escape velocity becomes c at the surface. It's a black hole now. Add more mass to raise the event horizon altitude.

[JamesC]

PlutonianEmpire:

Neutron stars have size and are made of regular matter albeit only neutrons.
Black holes have no size: They are points. They have NO identifiable constituent matter (which has size).

In the neutron star, you have regular material organised in three dimensions - except that it's so massive, hence so dense - that electrons are squashed into protons - giving a neutron.
More simply: gravitational pressure is so great that neutrons are the only atomic components (baryons) that can exist.

In a black hole, gravitation is so great that everything is INFINITELY squashed: NO matter can exist at all - and the black hole has zero size - it's a "singularity" (means "singular" or "special case"): work out density of a black hole and you have "mass of black hole / zero = undefined - infinite.".

Why the event horizon:
The escape velocity increases as you approach anything, but it's always finite - except for black holes!
Get close enough to a black hole, and it's greater than the speed of light , and nothing can escape - because light can't, and nothing can go faster: that's the event horizon.
With a neutron star, that never happens - a neutron star is never heavy enough (or it would collapse and no longer be a netron star - but be a black hole of zero size).

Finally, the only way a black hole has any exchange with the world outside it's event horizon is via spontaneous creation of particle/anti-particle pairs. This happens everywhere, throughout space, all the time - all around us. Particle/anti-particle pairs come into existence out of nothing and nearly instantaneously annihilate.
If this happens AT the event horizon, then, by definition, one half of that particle/anti-particle pair cannot escape.
The result is a small, continuous, emission of particles (and anti-particles) from the surface of a black hole.
In this way, the black hole will very slowly lose mass: Basic conservation of mass says that if matter is radiating away from it, then it's losing mass.
That's Hawking radiation.

And incidentally - none of this, obviously, happens with a Neutron star because a Neutron star does not have an event horizon - because it isn't a black hole.

So Hungry4info:

you're right - except that your neutron star with an escape velocity greater than the speed of light is no longer a neutron star: Look inside (except you can't) and you'd find nothing: A zero-dimensional point of infinite density. No neutrons can exist inside that.
But it's the only way you can have an escape velocity greater than the speed of light - so it's a consistent picture.

julesstoop:
See above: an event horizon means escape velocity greater than c which implies a singularity - without the singularity, you don't get the event horizon - it falls out of the general relativity formalism.

[PlutonianEmpire]

Thank you for the info!

[Hungry4info]

JamesC, I am having difficulties grasping the idea that proton + electron = neutron.

You wrote that electrons are squashed into protons, creating a neutron. While I can see how this makes sense from purely the standpoint of the charges of the particles, I am not sure how this makes sense when considering the construction of a proton compared to an electron.

A proton is made of two up quarks and a down quark.
A neutron is made of one up quark and two down quarks.

But with electrons being fundamental particles, how does squashing them with protons make a proton a neutron? Does the electron somehow convert one of he proton's up quark to a down quark?

Also when considering mass,
neutron mass = 1.67492729 * 10^-27 kg
proton mass = 1.672621637 * 10^-27 kg

Resulting in a difference in mass of ~20000000 * 10^-37 kg.
So if electron mass = 9.10938215 * 10^-37 kg, then wouldn't it take a huge amount of electrons to be added to the proton to achieve a neutron-mass?

I only barely grasp particle physics, so I'm quite readily able to admit I could be very confused.

[JamesC]

Hungry4info:

Well, I'm casting my mind back to what we learnt years ago in particle physics and I've forgotten most of it.

Anyway: What I do remember is:
- In a nuclear fission or fusion reaction (using the term loosely because e- + p+ => no isn't fusion)
... mass is not conserved.
Mass can be converted to energy, or energy to mass - or both simultaneously.

- You quark question has me stumped: I don't know.
But I do remember that a neutron star is a neutron star because all protons become neutrons - I can't remember the reaction.

So at this stage I can do more more than root around the web where I find
http://www.scienceclarified.com/Mu-Oi/Neutron-Star.html
which repeats what I said and doesn't answer your question: Just that a neutrino is emitted.
Still, we're clear that protons + electrons => neutrons

I can't find any more precise explanation: But I suspect your mention of quarks is part of the answer - there must be some quark modification somewhere: an up changing to a down.

A textbook, or someone from high energy physics could answer this in a trice.

[Fenerit]

And how neutrons doesn't longer decay (beta) to re-gives protons?

[Hungry4info]

I would assume that a free neutron decays if it has more energy than its environment. Perhaps the extreme conditions in a Neutron star can keep the neutrons... neutrons.

And I thought neutron stars had outer layers containing regular nuclei, and that just the interiors of neutron stars were neutron-dominated.

Edit:
This paper describes the structure of a neutron star, and claims that the outer layers are electron rich, while getting more and more neutron-rich further in. (PDF)
http://arxiv.org/PS_cache/arxiv/pdf/090 ... 4475v1.pdf

[julesstoop]

[b]
And incidentally - none of this, obviously, happens with a Neutron star because a Neutron star does not have an event horizon - because it isn't a black hole.

Just a few mental experiments:

A bubble filled with air at Earth's atmospheric pressure (at sea level), but about as large as the size of Neptune's orbit, would generate enough gravity to have an event horizon and be a singularity. Now - obviously - this bubble would collapse into a much smaller size quite rapidly (and probably explode consequently in a supernova-like event because of the released gravitational energy, etc..), but consider this thought experiment. What if we could instantly create two such bubbles, one just heavy enough to have a larger escape velocity larger than c at the edge, and one just slightly less big/massive.

What would we be able to seen and measure as they collapse, from the inside as well as the outside. Would it be more or less the same, or would it be completely different because of the fact that some essential properties of one of these bubbles has crossed the boundary to trans-Einstanian physics?

Another thought experiment. What if we were to build a globular and differentially rotating structure, from some very strong material, with the same size and average density. But just not heavy enough to have an event horizon. Next we would subsequently add the last bit of material, just by letting the last pound fall in, to make it a singularity. What would happen? Would it instantly become something different altogether?

[Fenerit]

Perso, I agree with JamesC. Apart mental experiments, in which can happen all, because a mental experiment can be so impossible that from impossible follow everything, in a black hole is achieved the complete transformation energy-matter into space-time tensor. As long as some matter rest, a black hole cannot be achieved, and therefore also an event horizon.

[Joey P.]

Here is an .stc for a hypothetical quark star:

Code: Select all

"Dan Phantom:Dark Danny:3C58:Quark Star"
{
   RA 360.0
   Dec 62.1
   Distance 10000
   SpectralType "Q"
   AppMag 8.17
   Radius 10
}