Can Neutron Star Become Black Hole

[CraigD]

Originally Posted by litespeed

I think a discussion of mass v mass velocity might help in discussion of BH creation. … Further, I suspect this high velocity mass colapse has relativistic components that enable an event horizon to form.

I’m guessing that by “mass velocity”, litespeed means relativistic or “dilated” mass, that is , where is rest mass?

To the best of my knowledge, all mainstream models of black holes reach roughly the same conclusion as previous post in this thread: that mass dilation isn’t a significant factor in, nor a large net increase in mass due to it necessary for the formation of black holes.

Originally Posted by litespeed

For instance, I have seen nothing that indicates simply adding mass to an existing body ever creates a BH. However, just about everyone agrees a spent star of sufficient mass creates a BH when it collapses.

Most of the non-fictional description of the formation of a black hole I’ve read consider the collapse of a star, because, I think, this is believed to be the most common way black holes form. However, rare scenarios, such as a neutron star stripping matter from a binary star companion, appear possible.

Originally Posted by litespeed

If this is true, then mass by itself is insufficent to create an 'even horizon'. …

This isn’t what classical mechanics, or its extension by General Relativity, predict.

For neutral, non-rotating bodies, the mechanics of black hole formation is simple: calculate the radius at which the body’s escape velocity is equal to the speed of light. This radius is its Schwarzschild radius, . If is less than the radius of the body , the body is a black hole. Although it’s less usual to mention the of non-black holes, all bodies have them, but for most, is much smaller . For example, the Earth’s .

Because is proportional to mass, while volume is proportional to the cube of radius , if one adds mass in any manner to a nonrotating body, its will eventually exceed its , and it will be a black hole.

When one considers realistic factors such as nonzero net charge and rotation, black hole mechanics become much more complicated, but if charge and rotation are below calculable critical values, the simple calculations provide adequate approximations.

It’s also important to note that physics predicts that not only can black holes form when mass increases, they can unform when mass decreases. Some theories of the far, far future of the universe predict a ‘black hole era” (different theoretical assumptions put this future at from to years) in which most mass and energy is captured in black holes, which eventually lose mass via Hawking radiation, leading to a subsequent “photon” or “dark” era that last more-or-less forever.

[Moontanman]

There might help visualize the photon sphere or orbiting photons of a black hole..

Inside a black hole

Photon sphere - Wikipedia, the free encyclopedia

[maddog]

Originally Posted by litespeed

Bassically, I am thinking about the limits of BH physics. Specifically, their gravitation is so extreme that I wonder about two things:

1) Could light, theoretically, go into orbit someplace near or past the event horizon; after all, it never gets back out.
2) Mass dialation could be so extreme that, at some point, even the BH would not have enough gravitational force to actually crush it into a singularity. [PS - I do not believe infinities of any sort exist in our universe, including singularities. But thats just me.]

1) Not in any way you could calculate (living outside in the "real" world). From your vantage point the mass and time of the object would be a complex value (a + ib) & so would not make any sense in ordinary orbital calculations. I suppose you could apply the principle of fractals and observe the orbits of calculations interating around on the "inside" of a fractal map. Though that is the gist of a totally other topic.

2) As Freezestar & CraigD intimated to your question -- not really. From the point of view sitting on the object there would be no mass dilation. So it's possible "Black Holeness" would behave normally.

2a) There is one exception (though since you don't believe in infinities -- would not be likely) and that is the concept of a Naked Singularity. I had always assumed these to be impossible (so did everyone else for a long time). A recent article in SciAm seems to think otherwise.

maddog

[litespeed]

Moontanman - You wrote; [I paraphraze] "If you accelerated a heavy neutron star to an appropriate percent of speed of light would it become a black hole?"

I think you hit the nail on the head. Theoretically, ANY tiny massive particle could become massive enough to become a black hole with the proper velolcity. So the question remains: Is accumulated mass [either acretion or dialation] sufficient for BH.

Or does sufficient mass also require velocity [momentum] crashing at high speed into a center point to produce BH? Here is perhaps an annalogy from a plutonium fishion bomb. No amount of plutonium accumulated into a sphere will go critical unless it is forced into a critical mass by compression.

...maybee...

[Moontanman]

Originally Posted by litespeed

Moontanman - You wrote; [I paraphraze] "If you accelerated a heavy neutron star to an appropriate percent of speed of light would it become a black hole?"

I think you hit the nail on the head. Theoretically, ANY tiny massive particle could become massive enough to become a black hole with the proper velolcity. So the question remains: Is accumulated mass [either acretion or dialation] sufficient for BH.

Or does sufficient mass also require velocity [momentum] crashing at high speed into a center point to produce BH? Here is perhaps an annalogy from a plutonium fishion bomb. No amount of plutonium accumulated into a sphere will go critical unless it is forced into a critical mass by compression.

...maybee...

Are you sure about that litespeed? I know it's not true for Uranium, adding uranium to a sphere will result in a low yield explosion but it will indeed go critical without being compressed. The idea behind the assembling it with an explosion is to do it all at once and result in a critical mass that results in more of the fissile material reacting, not compression.

[HydrogenBond]

Neutrons are not single particles but are composed of substructure. The substructure is not stable outside the superstructure containment, since we don't have a jar of quarks. Once they leave the superstructure, in accelerator experiments, they quickly disappear. All that has to happen to a neutron star is add enough gravity compression until the substructure comes outside the neutron superstructure and we get a poof; black hole. An acceleration collapse of a large star adds extra pressure, so we can get the poof starting with less mass. But we should get the same effect by adding extra mass-gravity-pressure to a neutron star.

[CraigD]

Originally Posted by litespeed

Theoretically, ANY tiny massive particle could become massive enough to become a black hole with the proper velolcity.

No, it can’t.

A general discussion of why it won’t is in A mass dilation “paradox” thought experiment, which addresses the apparent paradox that arises from a body having different masses when measured by observers with different velocities relative to it. The following thought experiment examines it more directly, by comparing a body that is a black hole due to sufficient rest mass, to one of the same mass because of a large speed relative to an observer,

This thought experiment has 2 parts: the first part considers the motion of a particle with non-zero rest mass and speed less than c interacting gravitationally with and ; the second considers the behavior of light.

Consider a body with rest mass and radius sufficient to be a black hole (eg: , , its event horizon) and a small (eg: 1 kg) body S near it (eg: 20000 m from ’s center) and at rest relative to it, both observed by a distant observer W at rest relative to . S is accelerated by the force of its gravitational attraction toward ( is also accelerated, but by such a small amount that it can be ignored), falling toward it at increasing speed until it passes the event horizon, and can no longer be observed.

Now consider a body with rest mass 1 kg and speed relative to S and W sufficient for it to have a relativistic mass of (about = 0.9999999999999999999999999999999 c). Depending on the position and velocity of relative to S, one of the following will occur:

• moves away from S before S is accelerated enough to collide with it.
• S accelerates, always decreasing the distance between it and , and its speed relative to , until they collide.
• S accelerates, decreasing its speed relative to , until they are a rest relative to one another. The force between them becomes very small, and they either eventually collide, drift apart, or orbit one another.

Unlike the scenario with , in many cases, S escapes from ’s gravitational field. In some cases, the relative speed of and S decreases, so the relativistic mass of as experienced by S decreases, in some cases until they interact like two 1 kg bodies.

In any case, what W observes is very different for and S than for and S. It’s also different than what W observes when is at rest relative to it, and S has a very high speed relative to them, because no matter what path S follows, it can never experience a decrease in the mass of , as it could in its interaction with .

The key idea of this thought experiment is that relativistic mass is dependent of relative motion. So, regardless of the speed of a body relative to some distant observer, it is the relative speed of the bodies interacting gravitationally that matter. If these relative speeds are too great, the bodies will move away from one another and cease to interact much gravitationally. If these speeds are too low, there won’t be much mass dilation.

Originally Posted by litespeed

Is accumulated mass [either acretion or dialation] sufficient for BH.

From calculation such as the Schwarszchild solution for a non-rotating black hole, we know that sufficient mass in any form within a sphere of sufficiently small radius is sufficient to form a Black hole. For the Schwarzchild solution, all that is necessary is that the mass is not rotating.

Originally Posted by litespeed

Or does sufficient mass also require velocity [momentum] crashing at high speed into a center point to produce BH?

None of the solutions for a black hole of which I’m aware require high speeds nor a crash into a center point. The solutions for a rotating black hole all explicitly forbid such a crash.

As noted in post #9, the real universe conditions involving black hole formation also preclude many massive bodies reaching very high speeds due to collisions. One can think of this a characteristic of reality that “abhors” many fast moving bodies occupying a small volume, so collisions tend to transfer momentum from fast to slow bodies, and remove energy in the for of radiation. A consequence of this is that the vicinities of black holes and other compact objects tend to be have hot disks and jets radiating in many bands of the EM spectrum.

There’s also fundamental reasons to believe that the classical (that is, not quantum) mechanics of Relativity fail at very small scales prohibiting very low mass bodies from having very great mass dilation. Were this not the case, situation in which, say, an electron and a positron fall toward one another from a great distance, are accelerated by a magnetic field, and orbit each other at a very close distance and very high speed, could result in sub-microscopic black holes with masses greater than stars. Quantum mechanics, with its requirements that particles obey rules of wave-particle duality, forbids such interactions.

Originally Posted by litespeed

Here is perhaps an annalogy from a plutonium fishion bomb.

I don’t think the analogy fits.

A fission bomb works by arranging atoms of fissionable elements so that emitted neutrons cause increased fission. Gravity is not important in fission bombs.

A black hole, a planet, or a star affects other bodies via gravitational force. The arrangement of matter that causes this force is not important. For example, a satelite’s orbit depends almost exclusively on the mass of its primary, very little on other characteristics.

Originally Posted by litespeed

No amount of plutonium accumulated into a sphere will go critical unless it is forced into a critical mass by compression.

As moontanman notes, this statement is incorrect. “Critical mass” means conditions in which a nuclear fission chain reaction occurs. As noted in the linked wikipedia article, a sphere of plutonium-239 massing more than 10 kg is supercritical.

[Pyrotex]

the first atomic bomb design was simply to make two semi-spheres of plutonium, which together added up to a critical mass. The two semi-spheres were kept separate in the bomb, separated by a long tube or "gun barrel". An ordinary explosive charge sent one semi-sphere down the barrel to collide with the other. No "compression" was involved. The bomb worked just fine.

[HydrogenBond]

Fission requires both a critical mass and a critical geometry. A fission bomb has the critical mass at the tip of the missile, but not in the critical geometry. This makes it safe, until we create the critical geometry, such as with a conventional explosion. When both requirements are met it goes critical. If we exceed the critical geometry it can go supercritical; boom.

The thing I never understood about a neutron star is where does all the energy go when all charge is neutralized and all the neutrons sort of fuse together? Will this energy output create one of the most powerful energy displays in nature? Or is all this energy absorbed by the neutron density, loosely analogous to forming atoms higher than iron, which absorb energy?

[CraigD]

Originally Posted by HydrogenBond

Fission requires both a critical mass and a critical geometry.

I was thrown off initially by the term “critical mass”, as it seems that “critical density” is a more accurate one. Critical mass is actually a mass, but depends on all the factors that affect fission, which include not only the element and isotope of the fissile material, its density, and temperature, but also any sort of neutron reflective casing material. This is the stuff of nuclear engineering and weapon design, information so specialized that it’s a state secret, the unauthorized acquiring and exchange of which can get you jailed in most nations. Even national weapon labs can’t always design a good fission bomb, as shown by North Korea’s 10/9/2006 test, which experts believe yielded about “fizzle” of 0.5 kT of a planned 5 to 15 kT.

I was fascinated reading about the history of early US fission bomb designing by the history of a 6.2 kg sphere of plutonium (mostly Pu-239) know as ”the Demon core”. On two separate occasions in 1945 and 1946, “slips” while arranging neutron reflectors around the core resulted in core and reflector assembly going critical, each time giving one person a fatal radiation dose, until it was finally disposed of later in 1946 as the core of a 23 kT test bomb.

Originally Posted by HydrogenBond

The thing I never understood about a neutron star is where does all the energy go when all charge is neutralized and all the neutrons sort of fuse together?

My understanding of what occurs when a neutron star forms from the core of an ordinary, atomic matter star, is that every proton and electron combine via inverse beta decay to form a neutron and a neutrino. This reaction does result in a net increase in energy, which is released in the form of the velocity of the weakly interacting neutrino.

The end result of all this, a neutron star something like a single atomic nucleus with a gigantic mass, but a relatively low charge, covered by a “crust” or ordinary matter that doesn’t undergo this transformation. This is in most part a tremendously large nuclear fusion event, which, resulting in a nucleus much more massive than a single iron nucleus, doesn’t produce, but requires a huge amount of energy. This energy comes from the change in gravitational potential energy of the whole system, an equally huge amount of energy.

Originally Posted by HydrogenBond

Will this energy output create one of the most powerful energy displays in nature?

While the energy carried by these neutrino is a huge amount of energy, because neutrinos interact so weakly with baryonic matter, it wouldn’t be a very powerful display – though if nearby enough, it should be detectable by neutrino detectors.

Originally Posted by HydrogenBond

Or is all this energy absorbed by the neutron density, loosely analogous to forming atoms higher than iron, which absorb energy?

Because neutrino’s interact with so weakly with baryons, I don’t think much of the energy from the inverse beta decay contributes to the energy requirements of the huge fusion event mentioned above.

Since unlike with a black hole, EM radiation can escape from a neutron star, and because it’s surrounded by a hot accretion disk of ordinary matter, some of it colliding with the neutron star's ordinary matter crust, neutron stars are still very bright, mostly in the radio and x-ray spectrum. When the neutron star has a strong magnetic field and rotation, its emissions can be “pulsed”, in which case it’s a pulsar.