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Star eating black hole





Ankhanu
Apparently a lingering bright flash from a distant galaxy is a star being consumed by a black hole:
ScienceShot: Powerful Jet Being Produced by Star-Eating Black Hole

Pretty crazy stuff. It should be interesting to see what information and theory is pulled from the data of this event over the next couple years.


Bluedoll
This is so interesting! Ok, kiss me or knock me head off if you want (means support of disprove the theory for the purpose of learning more about black holes) Laughing
Quote:
While gas accretion onto some massive black holes (MBHs) at the centers of galaxies actively powers luminous emission, the vast majority of MBHs are considered dormant. Occasionally, a star passing too near a MBH is torn apart by gravitational forces, leading to a bright tidal disruption flare http://www.sciencemag.org/content/early/2011/06/15/science.1207150.abstract
First of all, thank you Ankhanu for raising up this wonderful picture, thanks to NASA for putting up the swift cam in the sky and thank you God for making the universe so beautiful.



Bluedoll’s Theory on a Black Hole Phoneme (conducted in the frihost labs)

Abstract
This is a picture of a conversion engine. What we see is a star being disrupted and great amounts of energy being released which enable us to see it. The engine converts matter (mostly in a gas state) to energy. Matter is not consumed but transferred from one place to another while great amounts of energy is positively being released and negatively transferred to the center. The black hole does not contain mass but energy of the negative variety. The gasses that are being dispersed around the center vary in colour. The brighter colours migrating to white are temperature related with the highest energy concentration inside the star and immediately outside the center of the hole. The high energy concentration around the hole disperses by way of attraction to the more massive negative energy potential of the hole.

The hole exists as a phenomena that has developed to collect negative energy but is so massive that positive energy is thrown off in the flare with the remaining negative energy being collected. Since the energy forces are so massive, mass is literally ripped apart and what is left is pure energy.
Ankhanu
I think you're going to provide some background material is this is going to make any kind of sense. For example, what is "negative energy", what is "positive energy"?

Some of it does tap in to existing hypotheses, for example, matter converting to energy beyond the event horizon, etc... but, by definition, a black hole contains mass; vast quantities of mass relative to its size.

Just gonna stick this out there, astrophysics is really not my thing. I have a grounding in classical physics and some relativity, but haven't done much beyond that level. A lot of the ideas that are important in addressing black hole physics properly are well beyond my experience Razz
Bluedoll
Quote:
Some of it does tap in to existing hypotheses, for example, matter converting to energy beyond the event horizon, etc... but, by definition, a black hole contains mass; vast quantities of mass relative to its size. – Ankhanu
Well, be assured this is totally my hypotheses, though I do suspect no one in this world can take credit for not tapping...i.e.: starting with Newton’s law etc.. and yes the abstract is declaring that black holes do not contain mass.

What then accounts for what Fred Zwicky observations (see kelseymh’s explanation on cluster rotation http://www.frihost.com/forums/vt-126124.html) is somewhat disturbing unless gravity could actually be affected by an energy source without mass. This may be an exercise of futility but I am convinced that there is something to be learned from any exercise.


Addenda to Bluedoll’s/ Ankhanu Theory on a Black Hole Phoneme

What is negative energy versus positive energy defined?
Of course we understand with electricity that in order for balance equilibrium events to take place (the universe is always seeking to find balance) there must be a negative and positive force present or even our computers would stop functioning. I am making the suggestion that larger events such as what we actually see now with the aid of our 21st century tools, a star follows the same order as anything else. Why not? Of course there are always exceptions and complexities but the general basics stay fixed.

In quantum field theory, the Casimir effect, Casimir–Polder force are physical forces arising from a “quantized field.” What the Casimir effect is from what I understand is simply a field that exists around matter that will affect another field associated close by. Though it is a theory, the idea could explain worm holes in space and makes a connect with gravitational force and with surrounding fields.

As with any field it would stand to reason that perhaps a polarity of sorts could exist? That might make for speculation concerning exotic matter, which is a purely mathematical hypotheses to explain dark matter. The existence of these fields however do require matter and all very bizarre work.

What I am postulating, given that all things are possible, is that fields can exist without mass if the forces are sufficiently established by extreme masses such as what we might experience around galaxies. What causes worm holes is anyone’s guess but obviously we have caught a glimpse of something fantastic in this picture. I am blown away – that would be literally as well.

So in conclusion, I am defining positive and negative energy as the building blocks of the universe starting on the atomic level and moving outwards to the universe. All force as we know it on earth of any kind are forces striving to maintain a balance and therefore is it not a reasonable assumption to include two distinctive forces in every activity. (going back to Newton)

The metamorphous of this star is showing us that force does exist we need only to find out and explain what forces are at work in this picture. Is it two masses at work, one in a gas state and the other in the massive black hole that contains mass but we can not see the mattering inside it? I know black hole mass is becoming accepted but that explanation seems so grotesque to me, sorry.
jwellsy
This looks like Hawking Energy to me.
http://en.wikipedia.org/wiki/Hawking_energy
Bikerman
There is a lot of nonsense being suggested here.
There is nothing unexplained about the photo - though it is a remarkable photo nonetheless.
It is known that there are a large number of binary star systems where one of the binaries is a BH. In this case the BH companion is sufficiently close to be dragging matter from its companion star. The ultimate 'resolution' will be that the BH 'eats' the companion star completely.

Hawking energy is entirely irrelevant to the picture. Hawking energy is the thermodynamic flow of energy from a BH when it is warmer than the surroundings. It means that over thousands of billions of billions of years a BH will eventually 'evaporate' - but only when the surrounding temperature is less than the temp of the BH.
Quote:
What is negative energy versus positive energy defined?
Of course we understand with electricity that in order for balance equilibrium events to take place (the universe is always seeking to find balance) there must be a negative and positive force present or even our computers would stop functioning. I am making the suggestion that larger events such as what we actually see now with the aid of our 21st century tools, a star follows the same order as anything else. Why not? Of course there are always exceptions and complexities but the general basics stay fixed.

Err...frankly this is incoherent.
The universe is not 'seeking' anything. The 2nd law of thermodynamics does indeed mean that energy will 'even out' over the available space. The concept of 'negative and positive' force is not something I can comment on - since it is clearly an invention based on...well, nothing I can relate to. The idea that our computers rely on this 'negative force' is simply wrong. Charge can be positive or negative, so I'm presuming that you mean current flow?
kelseymh
Bikerman wrote:
There is a lot of nonsense being suggested here.
There is nothing unexplained about the photo - though it is a remarkable photo nonetheless.


I hate to break it to all of you guys, that is not a photo! It is an artist's conception (in other words, a cartoon) of the process which is believed to be going on, based on the observations from SWIFT, Chandra, etc.

Quote:
It is known that there are a large number of binary star systems where one of the binaries is a BH. In this case the BH companion is sufficiently close to be dragging matter from its companion star. The ultimate 'resolution' will be that the BH 'eats' the companion star completely.


Etc. The rest of Bikerman's posting is right on. The nonsense posted elsewhere in this thread is completely irrelevant to simple magnetohydrodynamics and theromdynamics of gas, dust, and plasma being heated by compression.
kelseymh
jwellsy wrote:
This looks like Hawking Energy to me.
http://en.wikipedia.org/wiki/Hawking_energy


Nonsense, and completely irrelevant to the situation described in the original posting.

Hawking radiation (as you would know if you actually read the above article) is thermal (that is, a black body frequency distribution) radiation hypothesized to be produced at the surface of a black hole. The temperature of the radiation is inversely proportional to the surface gravity (which is proportional to surface area) -- large black holes have a low temperature.

The scaling relationship is such that a black hole of one solar mass (smaller than any observed astrophysical object, by the way), would have a temperature of 60 microkelvins (that is, 0.000060 degrees above absolute zero). Larger black holes would have proportionally smaller temperatures: the SMBH at Sagittarius A* (the center of the Milky Way), with a mass of 4.3E+6 solar masses, has a temperature of 14 trillionths of a degree above absolute zero (14 picokelvins).

The ambient temperature of the universe is 2.7 K, and the local temperature of the gas and dust around astrophysical black holes is much higher than that. It is trivially obvious that astrophysical black holes do not emit Hawking radiation, since they are (by definition) colder than their surroundings.
kelseymh
Utter, complete nonsense, predicated upon a clear absence of any knowledge of astrophysics, but filling in the gaps with lots of cool, sciency-sounding words. Let's start at the beginning and go on from there.

Bluedoll wrote:
Bluedoll’s Theory on a Black Hole Phoneme


1) This isn't a theory, it is, at best, a hypothesis. More accurately, it is speculation.

2) I don't think you're trying to describe a linguistic unit of sound.

Quote:
Abstract
This is a picture of a conversion engine.


This is an artist's conception of a star being tidally disrupted by an unseen massive object. The gas and dust which have been pulled away from the star form a thick ring (an accretion disk) around the central mass, quite similar to the visible ring's around Saturn (which formed by tidal disruption of former moons).

Quote:
What we see is a star being disrupted and great amounts of energy being released which enable us to see it.


Correct, and adequately adapted from the caption of the picture. This artist's conception carciatures a physical process which we theorize underlies the long duration X-ray emission from a particular source which has been observed by satellites.

Quote:
The engine converts matter (mostly in a gas state) to energy.


Wrong. The X-ray emission we observe is produced by two very simple, very well understood physical processes which we can replicate in the laboratory. The first is simple gas compression. As the gas and dust fall from the donor star's orbit down closer to the central mass, it is compressed. The gas laws tell you that as you compress a gas, you raise its temperature. In this case, the temperature of the innermost part of the accretion disk is high enough to be glowing mostly in X-rays, rather than in visible or infrared light.

The second process is synchrotron radiation. What I have been calling a "gas" is more accurately described, especially in the inner part of the accretion disk, as a plasma -- a gaseous state in which electrons have been stripped from atoms, so that you have a mixture of charged particles (electrons and ions), rather than neutral atoms. The central mass also has a strong magnetic field, which we can measure from the Zeeman splitting of spectral lines; charged particles moving through magnetic fields have their trajectories bent, and emit electromagnetic radiation (called synchrotron radiation) as a result.

Quote:
Matter is not consumed but transferred from one place to another while great amounts of energy is positively being released and negatively transferred to the center. The black hole does not contain mass but energy of the negative variety.


More sciency-sounding words strung together without comprehension. Black holes contain mass -- a trivial consequence of the fact that they exert a gravitational force. We can measure that mass in a number of ways, the simplest being to simply observe the orbital period and distance of a companion orbiting the black hole.

Quote:
The gasses that are being dispersed around the center vary in colour. The brighter colours migrating to white are temperature related with the highest energy concentration inside the star and immediately outside the center of the hole.


Because the artist who painted this cartoon decided to do that. He or she probably chose it as a simple convention to represent the temperature variation across the disk, as you suggest.

Quote:
The high energy concentration around the hole disperses by way of attraction to the more massive negative energy potential of the hole.


More sciency-sounding words strung together without comprehension. What exactly are you trying to describe here?
Bluedoll
Perhaps it is better to put out a question. Is it possible that the phenomena (what we are currently observing in space) and what many people are referring to be a black hole does not contain mass but what does exist is for other reasons other than our present understanding of what a black hole is?


This really sucks, well the Bluedoll’s Theory on the whole, was only a theory, nope, actually a speculation, nope, actually really only a learning exercise. Science is fascinating. Great posts by the way, on this very cool picture and the greatest education, I think was the picture was really a cartoon.

On the cartoon, just a tad more focus on that – so, what we are learning here is that sat's launched into deep space that measure x-rays and based on that and very small visual dots of electro-magnetic radiation, enable us to make calculations that can determine orbits, mass and of course some very interesting theories, correct, I think?

What I find equally interesting along with the discovery's is.... if we all stand back for one moment and compare the cartoon to the reality, they are much different. A question of what theory is comes to mind. As I understand it and correct me if this is wrong, a black hole is a theory, it has not been verified, yet black holes are almost commonly accepted as a reality by many? Why?

Is the answer because we see more of the sensational, because we put expensive sat's into space that can measure x-rays or that we can now draw better cartoons? I still think it is fantastic, do not get me wrong but unless I am out of touch with what is going on in the science world presently and that is very possible, as my science teacher walked the floor many years ago but took an enormous amount of time with us to explain the difference between reality and a theory.

Now , I am getting even more information on this very interesting subject but there are still questions here. Do black holes exist just as the theories say they exist?

Is a black hole a great giant mass of sticky muck in a very cold state with huge gravitational force that is capable of sucking in anything it comes into contact with including electromagnitic radiation, then after it does over a long wait of course, it just pees it out. Unless, I am wrong a black hole is nothing more than a theory. What we are actually observing in space today most likely in the distant future will look something to people like what Galileo looks like to us now and the hardware will be available at the local mall in the toy department.

Is it even remotely possible, though even if it is spacey speculation that a black hole may not be composed of matter or not? If this is not possible and we find that the conception we now have of a black hole is completely accurate then I will not be heart broken simply because I have learned a little more today about science than I knew yesterday, that being I hope not nonsense, and completely irrelevant to the situation . Smile
kelseymh
Bluedoll wrote:
Perhaps it is better to put out a question. Is it possible that the phenomena (what we are currently observing in space) and what many people are referring to be a black hole does not contain mass but what does exist is for other reasons other than our present understanding of what a black hole is?


Black holes (that is, a density singularity surrounded by an event horizon) is a solid mathematical prediction of general relativity. GR has been tested experimentally to roughly one part per billion (not as good as quantum electrodynamics, at one part per trillion, but close), and no deviations have been found. The mathematics of black holes are extremely solid, and based in mathematics (solutions to coupled partial differential equations), not just in observation.

There are other hypotheses out there for what happens astrophysically when a mass greater than the Chandrasekhar limit collapses (look up "collapsar" or "MECO" in Wikipedia), but neither of those hypotheses make testable predictions yet.

Quote:
On the cartoon, just a tad more focus on that – so, what we are learning here is that sat's launched into deep space that measure x-rays and based on that and very small visual dots of electro-magnetic radiation, enable us to make calculations that can determine orbits, mass and of course some very interesting theories, correct, I think?


Astrophysical observations have been going on for centuries. They don't have to rely on satellites -- we use satellites in order to see radiation (such as infrared, X-rays, gamma rays, and primary cosmic rays) which does not penetrate the Earth's water-laden atmosphere.

We determine orbits based on many observations, so that we can plot position versus time, and apply Kepler's laws (that's another keyword you can go and research).

Quote:
As I understand it and correct me if this is wrong, a black hole is a theory, it has not been verified, yet black holes are almost commonly accepted as a reality by many? Why?


See above. The mathematics behind black holes are extremely well founded and well studied (and if you are not versed in those mathematics, then you are simply not competent to propose a competing theory). Observationally, we have two systems, M87 and Sgr A* (two more keywords for you to go and research), which have been observed to sufficiently high resolution that we can see stars orbiting them at veryclose distances.

Those orbits are so close that in order for the central mass to exist, it must be inside a volume much smaller than the neutron degeneracy limit. Within that limit, there is no known force (yes, I know) which can exert a pressure stronger than gravity. Consequently, the mass which is there must have collapsed beyond the event horizon, forming what is by definition a black hole.

Quote:
Is a black hole a great giant mass of sticky muck in a very cold state with huge gravitational force that is capable of sucking in anything it comes into contact with including electromagnitic radiation, then after it does over a long wait of course, it just pees it out.


Not at all. Black holes don't "suck anything in", any more than the Earth or the Sun "suck things in." They are simply masses, around which objects can orbit just like any other mass. The difference is that objects can get much closer to the center than for most ordinary masses, and when you get that close, the forces you experience are much stronger than we ordinarily deal with.

Here's a simple example. Suppose that, through some magic, the Sun right now turned into a black hole. Not exploding, not a supernova, just instantly
and quietly collapsing. About the only thing you would notice is that the sky would suddenly turn dark and the stars would come out. The Earth would continue on its same orbit, and so would all the other planets (including Mercury!). Why? Because we are far from the center of the sun, and the gravitation force is determined simply by the mass and the distance.

Black holes are only interesting once you get really close to them. For most objects, in order to get that close to their center you have to be inside them, and gravity inside an object gets weaker the closer you get to the center (there's less mass below you). With a black hole, no matter how close you get, all the mass is still below you. So gravity just keeps getting stronger.
TheMatrixDNA
quote="Bluedoll"]I am out of touch with what is going on in the science world presently Smile[/quote]

Bluedoll,

Maybe this is a good thing. Maybe our scientific thought today is away off the beam ( it happened several times before), and those indoctrinated by scholar education will never be able to think out of the box. I will try to explain in English how our scientific world vision today could be wrong.

Think about a human body. We have the hard skeleton, muscles and covering it, the soft meat. What can do Physics and Mathematics studying this body? It can describe and making right previsions about the skeleton, even the muscles, but when arriving at the soft level, almost nothing it can do here. The language now is Biology and Natural Systems, not Mathematics. And when we arrive at the mental level? Emotions, feelings, psychology? Physics and math has nothing to do here.

Now let’s go to the Cosmos, Universe, astronomical systems. First of all, it is rational to think that the biological phenomena and language presents at living beings must have be presents before, since the Big Bang. The Physics brutes’ forces and mechanical interactions between astronomic bodies must have the principles of life’s properties. So, it is possible that all this cosmic stuff is covered by a layer of phenomena ruled by life’s properties. We cannot see it due our relativist position as observer in relation to time and space. Since that a birth of a new star must takes millions or billions of years, we never will watch such event, so, we never will have a scientific statement about. We have only theories.
But…man cannot stop its curiosity and will for understanding our existence. We have no scientific resources for to grasp the upper level of rules translated by Biology at galaxies, but we need theories, explanations. Then we have used what we have at hands: Physics and Mathematics. But math is the language of the skeleton only and it is relative to reduced phenomena. It cannot grasp the mechanisms and processes about systems.

So, we that could not follow Science in the university but we love science and we need to understand the world, we are not indoctrinated and we produces different theories. In relation to academic science our theories will be away off the beam, like was Copernicus, Galileo, Darwin, in relation to the universities at their times.

I lived at Amazon jungle during seven years. My worst discomfort was that could not to follow the scientific evolution by our civilization. But there I was doing my research, about the natural systems that constitutes the whole biosphere. From here I was launched to search the causes of biosphere in the atmosphere and from here, to the Cosmos. So, I made the reverse way than scientific civilization was doing. Instead applying the Physics of the beginning to understand the galaxies structure, I applied the biology of the endings. I got a different world vision, maybe it is away off the beam. But, the artistic draw above, made only yesterday by NASA’s orientations, I made the same draw 20 years ago, when calculating how could be the astronomical system that produced such things like the DNA.
In my models there is no such thing like the black holes described by academic theory. What they think should be a black hole at the center of certain stars orbits, in my models are merely nuclear vortex of rotational mass composed by dust of died stars. My models predicted the burst of strong jets of gamma rays from the galactic nucleus, but it is about the birth of a new star and not the death of a star being eating by a black hole.

There is no scientific conflict between my draw and the draw above. Because the scientific real fact is the registration by the sat’s about a burst of gamma ray at certain region. Science finishes here and from here, began the explanative hypothesis. The above draw is suggesting that the star has a tail of its matter going inside a black hole. The scientific fact is only a burst of gamma ray, so, the tail is hypothetical. And people here are thinking about the draw as the tail is intrinsic to the phenomena. It is not, yet. It is their hypothesis today. If you want to see how the Cosmos could be covered by a biological layer that explains the production of life here, see the models at my website. I would appreciate your comments about since I am continuing searching the thru.
Bluedoll
Quote:
Black holes are only interesting once you get really close to them. For most objects, in order to get that close to their center you have to be inside them... - kelseymh
The links suggested were really helpful and the idea that a black hole does not necessarily change gravitational properties (our sun collapsing) until you get very close is much different than I thought was being theorizing about them, thank you for that.

I am struggling with the Chandrasekhar limit. I think of a collapsing star like a big engine with a blown gasket, first the gasket goes then I blow my gasket when I find out the price!

I understand stars are like an engine as discribed by ‘main-sequence’ they are in an equilibrium state. That is outward thermal pressure from the hot core balances out the gravitational pressure from the overlying layers. There is so much mass that nuclear fusion of atomic nuclei (can be hydrogen) smuck together, and then change to another state. We know when things change state, like our fireplace wood did that evening as it turned into ash or like me with my blown gasket, it means a release of energy.

Now I read that the electron degeneracy pressure which is what controls or keeps in check the star's keep the fires burning process. The behaviour of matter might take us then to a study of fermion and bossoms, again so interesting? But so to keep on track here, when stars stop doing what they are designed to do and give it up for the group ‘collapse’, they do so because the mass that is above is over the limit of the inner pressure in the core and insufficient to balance the star's own gravitational self-attraction. (over the chandrasekhar limit pancake mix)

This to me is like saying my bread fell in because my liquid dough did not have enough strength to hold together when it started to rise.

Maybe where my confusion is what change in overall nuclear composition takes place in a star to cause it to fail and degenerate? What is left over after the failure is equally as confusing but I like that the questions are endless.

Quote:
The Physics brutes’ forces and mechanical interactions between astronomic bodies must have the principles of life’s properties.- TheMatrixDNA
I relate well to this idea because to me it does make the most sense of anything – and want to look at your site next. – thank you.
kelseymh
Warning! This is a very long post, with a lot of detail. I am not providing supporting links to everything; you can either get yourself a good undergraduate textbook on astrophysics, or use the keywords to go look things up on Wikipedia. If you don't believe what I write, and can't be bothered to go and verify it, that's your problem, not mine.

Bluedoll wrote:
Quote:
Black holes are only interesting once you get really close to them. For most objects, in order to get that close to their center you have to be inside them... - kelseymh
The links suggested were really helpful and the idea that a black hole does not necessarily change gravitational properties (our sun collapsing) until you get very close is much different than I thought was being theorizing about them, thank you for that.


Great! The idea that black holes "suck material in" has been spread around by popularizations (especially journalistic ones and movies), to the point that non-physicists all seem to think it's true. And it causes no end of confusion and misunderstanding. I'm glad I was able to give you a nudge in the right direction Smile

Quote:
I am struggling with the Chandrasekhar limit. I think of a collapsing star like a big engine with a blown gasket, first the gasket goes then I blow my gasket when I find out the price!


Very Happy The point is basically that because there are different forces involved when you get to different energy scales (temperatures), stars (or more generally, balls of gas) can be supported against gravity in different ways. See below.

Quote:
I understand stars are like an engine as discribed by ‘main-sequence’ they are in an equilibrium state. That is outward thermal pressure from the hot core balances out the gravitational pressure from the overlying layers. There is so much mass that nuclear fusion of atomic nuclei (can be hydrogen) smuck together, and then change to another state.


Correct. When a star is burning nuclear fuel (whether hydrogen, or something else in older stars), that burning produces heat. That heat creates pressure in the gas/plasma, and that pressure keeps the star "inflated" while gravity is trying to pull everything down.

Quote:
Now I read that the electron degeneracy pressure which is what controls or keeps in check the star's keep the fires burning process.


Not exactly. You've skipped a step. Stars burn different fuel as they age. Young stars, and main sequence stars like the sun, burn hydrogen into helium. The energy released by this process heats the plasma and keeps the sun inflated. At the same time, the helium, being denser than hydrogen, migrated inward under gravity and slowly builds up around the center of the sun.

Eventually (about 5 billion years from now), so much of the hydrogen will have been burned that the Sun can't use what's left to stay inflated. It'll start to collapse, heat up (compressing a gas raises its temperature), and get hot enough to burn the helium that's collected at the core. Burning helium produces carbon, and from carbon you can get to heavier elements (nitrogen, oxygen, neon, silicon, blah blah blah) all the way up to iron in the most massive stars.

Whatever fuel is being burned, eventually it'll run out, the fusion process will cool, and the star will collapse again, but this time the compressive heating won't be enough to start another fusion process. Instead, the star will keep shrinking, and heating, until all of its material is fully ionized -- a plasma of electrons and ions. At that point, instead of heat creating pressure, there is something new. A "force" which results from the rule that spin-1/2 particles (like electrons) must all be in different quantum states (different momenta, different energy levels, different spin orientations, and different locations). This rule is called Fermi-Dirac statistics, and the particles which obey that rule are called fermions.

If you work out the math for how many electrons there are in the Sun, and ask how far apart you can put them and still satisfy Fermi-Dirac statistics (use the electron's de Broglie wavelength as a proxy for "size"), you will discover that the Sun could be collapsed into a ball roughly the size of the Earth (a white dwarf). If you try to make it smaller, the electrons overlap too much and violate the rule. We call the application of this rule degeneracy pressure (two particles with identical quantum states are called degenerate in physics, just like the "degenerate solutions" to an equation in algebra).

Quote:
But so to keep on track here, when stars stop doing what they are designed to do and give it up for the group ‘collapse’, they do so because the mass that is above is over the limit of the inner pressure in the core and insufficient to balance the star's own gravitational self-attraction.

This to me is like saying my bread fell in because my liquid dough did not have enough strength to hold together when it started to rise.


Yes, this is exactly the right way to think of it! Mass is mass, and all it does is pull inward under gravity. But that mass is made up of particles with all sorts of interesting and useful properties in addition to mass. When they are atoms or nuclei, they can burn (fuse), and release energy which produces thermal pressure. When they are a gas of electrons (fermions), the requirement that the total wavefunction be antisymmetric leads to an effective pressure that keeps the material at a certain minimum volume.

Quote:
Maybe where my confusion is what change in overall nuclear composition takes place in a star to cause it to fail and degenerate?


The first step, getting to a white dwarf, is pretty simple, and extremely well understood (we have to understand it to build nuclear bombs, so the research was paid for quite handsomely :-/). Fusing hydrogen to helium releases a certain amount of energy per interaction; this is called binding energy. From helium to carbon doesn't release quite as much. Fusing carbon with hydrogen to get nitrogen releases even less, and so on, and so on. Each step in building up from hydrogen to heavier elements releases some energy, but not as much as the previous step.

Now, when you measure nuclear binding energies, you discover that the maximum (or minimum, depending on your perspective) value occurs with the isotope iron-56. If you try to take iron-56 and add a proton to it (to make cobalt-56) you don't get any energy back! You have to use extra energy to force the proton in there. And that remains true for all the elements (isotopes) heavier than Fe-56: you cannot get any energy back from the fusion process.

So once a star has undergone enough fusion that it's making iron, it's screwed. Sooner or later (mostly sooner), it will stop producing excess energy (heat), and the house of cards keeping it inflated will collapse, leading to a white dwarf (or something; see below).

But wait, there's more! I said above that electron degeneracy can be treated as an effective pressure which holes the white dwarf inflated against gravity. You can make that quantitative, and actually compute the pressure (in pounds per square inch, or atmosphere, or whatever you want), and it is a number. A specific, finite quantity. But if I keep adding more and more mass to my white dwarf, the gravity gets stronger and stronger (duh). At a high enough mass (above Chandrasekhar's limit) the inward pull of gravity is higher than the outward push of degeneracy pressure.

So what happens? The star doesn't violate the laws of physics -- the electrons don't get closer together than Fermi-Dirac statistics allow. Instead, what happens is "inverse beta decay" (a kind of radioactivity): the electrons collide with and get absorbed by all the protons and other atomic nuclei crammed into that same small volume. An electron plus a proton makes a neutron (with a neutrino emitted to carry away the extra energy). So very quickly (this is a Type Ia supernova) the white dwarf goes from being a giant ball of plasma to being a giant ball of neutrons.

Now, neutrons are also fermions, so they are also subject to Fermi-Dirac statistics. But neutrons are much more massive than electrons, with a correspondingly much smaller de Broglie wavelength. If you do the same calculation I referred to above, you'll discover that a solar-mass worth of neutrons will fit into a sphere about ten kilometers across (a neutron star). These neutrons are still being held apart by degeneracy pressure.

Let's just keep this party going, shall we? Start dumping mass onto your neutron star. It'll get more and more massive, but the degeneracy pressure will hold the ball of neutrons inflated against gravity. For a while. If you dump more than a few solar masses onto a neutron star (the exact value depends on detailed models of NS internal structure, and is an active area of research), then the inward pull of gravity will once again exceed the degeneracy pressure. But this time there's nothing, so far as we know, to exert a stronger pressure and stop the collapse. If the neutrons decomposed into their constituent quarks, the degeneracy pressure is lower (because the quarks are nearly massless, like electrons, and have a large de Broglie wavelength).

So what you end up with, dumping too much mass onto a neutron star, is a black hole. The matter just collapses, until the whole sphere is smaller in size than the event horizon for that mass. At that point, we have no way to observe the internal consequences (we assume the matter collapses to a point, a singularity of infinite density, or maybe quantum gravity takes over and prevents the singularity), but we are left with a very small volume of space with a whole lot of mass.
Bikerman
Thanks Mike. Personally I found that a useful refresher in the main - with a couple of details I'd not thought through myself yet. I'm sure that the general reader will find this a very approachable way into the whole topic.
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