(Caption) One step closer to a black hole? A hypothetical strange star results from extreme gravitational compression overcoming the strong interaction that holds neutrons and protons together. Credit Swinburne University - astronomy.swin.edu.au

Astronomy Without A Telescope – Strange Stars

7 Aug , 2010

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Atoms are made of protons, neutrons and electrons. If you cram them together and heat them up you get plasma where the electrons are only loosely associated with individual nuclei and you get a dynamic, light-emitting mix of positively charged ions and negatively charged electrons. If you cram that matter together even further, you drive electrons to merge with protons and you are left with a collection of neutrons – like in a neutron star. So, what if you keep cramming that collection of neutrons together into an even higher density? Well, eventually you get a black hole – but before that (at least hypothetically) you get a strange star.

The theory has it that compressing neutrons can eventually overcome the strong interaction, breaking down a neutron into its constituent quarks, giving a roughly equal mix of up, down and strange quarks – allowing these particles to be crammed even closer together in a smaller volume. By convention, this is called strange matter. It has been suggested that very massive neutron stars may have strange matter in their compressed cores.

However, some say that strange matter has a more fundamentally stable configuration than other matter. So, once a star’s core becomes strange, contact between it and baryonic (i.e. protons and neutrons) matter might drive the baryonic matter to adopt the strange (but more stable) matter configuration. This is the sort of thinking behind why the Large Hadron Collider might have destroyed the Earth by producing strangelets, which then produce a Kurt Vonnegut Ice-9 scenario. However, since the LHC hasn’t done any such thing, it’s reasonable to think that strange stars probably don’t form this way either.

More likely a ‘naked’ strange star, with strange matter extending from its core to its surface, might evolve naturally under its own self gravity. Once a neutron star’s core becomes strange matter, it should contract inwards leaving behind volume for an outer layer to be pulled inwards into a smaller radius and a higher density, at which point that outer layer might also become strange… and so on. Just as it seems implausible to have a star whose core is so dense that it’s essentially a black hole, but still with a star-like crust – so it may be that when a neutron star develops a strange core it inevitably becomes strange throughout.

Anyhow, if they exist at all, strange stars should have some tell tale characteristics. We know that neutron stars tend to lie in the range of 1.4 to 2 solar masses – and that any star with a neutron star’s density that’s over 10 solar masses has to become a black hole. That leaves a bit of a gap – although there is evidence of stellar black holes down to only 3 solar masses, so the gap for strange stars to form may only be in that 2 to 3 solar masses range.

By adopting a more compressed 'ground state' of matter, a strange (quark) star should be smaller, but more massive, than a neutron star. RXJ1856 is in the ballpark for size, but may not be massive enough to fit the theory. Credit: chandra.harvard.edu

The likely electrodynamic properties of strange stars are also of interest (see below). It is likely that electrons will be displaced towards the surface – leaving the body of the star with a nett positive charge surrounded by an atmosphere of negatively charged electrons. Presuming a degree of differential rotation between the star and its electron atmosphere, such a structure would generate a magnetic field of the magnitude that can be observed in a number of candidate stars.

Another distinct feature should be a size that is smaller than most neutron stars. One strange star candidate is RXJ1856, which appears to be a neutron star, but is only 11 km in diameter. Some astrophysicists may have muttered hmmm… that’s strange on hearing about it – but it remains to be confirmed that it really is.

Further reading: Negreiros et al (2010) Properties of Bare Strange Stars Associated with Surface Electrical Fields.

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Vanamonde
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Vanamonde
August 7, 2010 6:16 PM

“However, since the LHC hasn’t done any such thing, it’s reasonable to think that strange stars probably don’t form this way either.”

Hey. it ain’t at full power yet! But I’m hoping that the theory that is would many more times the power and luminosity than the LHC to make stable stranglets is right. Our confidence’s is high.

jimhenson
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jimhenson
August 8, 2010 6:33 AM

electrons flow around the surface of neutron stars and topological insulators. Perhaps an electron star briefly forms by a condensed matter state before total anti-matter annihilation of particle pair production occurs, leaving or forming a black hole? Quantum and macro states seem proportionally related to charges and their distances apart explainable without gravity by condensed matter plasma physics. Black holes have no size ranges, so perhaps all stars including tiny dwarf stars are in the same charged plasma medium pervading the universe, and are forming the early big-bnags missing neutron galaxies, as all normal galaxies having black hole central cores build up denser neutron star concentrations over time.

Uncle Fred
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Uncle Fred
August 8, 2010 12:47 AM

Wow. That’s a lot of strangeness!

Do we know enough to reasonably confer that these Strange Stars would be the final, and highest density objects before encountering Black holes?

Also, I’m unsure of how such an object would become a Black Hole if it were to eat enough mass. I have difficulty envisioning how all this works and looks to an outside observer. Would the event horizon grow from within and the star’s surface disappear behind it? Just curious..

DrFlimmer
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DrFlimmer
August 8, 2010 2:20 AM
It is likely that electrons will be displaced towards the surface […] Question: Where do the electrons come from? I mean, firstly they all merged with protons to build neutrons. And now it has just happened that the neutrons cracked up into “strange matter”. I don’t see from where the electrons should come back. Or does it have to do with the appearance of the strange quarks (which weren’t around before, either)? But no, this cannot be, since both down and strange quarks have the same charge (-1/3 e), and the strange quark should be made from a down quark (in neutrons we had up:down:strange = 1:2:0 …. in strange matter this is according to the text 1:1:1,… Read more »
Torbjorn Larsson OM
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Torbjorn Larsson OM
August 8, 2010 5:14 AM
If it happens, it will inaugurate a pleasing (and hopefully informative) state between microstate baryonic matter and the more or fully macrostate black hole. I’m unsure of how such an object would become a Black Hole if it were to eat enough mass. Aren’t we all? AFAIU the manner of transition would depend on how much of a coherent state the system is in before and after. Does it transit between states or does the system trajectory go between many states? I have difficulty envisioning how all this works and looks to an outside observer. And any coherence could have implications for how the whole mess couples to semiclassical theory (“QM+GR”). But in general I believe since the… Read more »
Torbjorn Larsson OM
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Torbjorn Larsson OM
August 8, 2010 5:19 AM

It hits me that I’m sloppy again: “event horizon growth” usually refers to its area growth. But that wasn’t what I was describing, or at least not all of it.

What should we call the gradual (or not) concentration of space-time curvature that happens when it instantiates? “Event horizon conception”?

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
August 8, 2010 5:47 AM
As for the electrons, yes, that is curious. The reference mentions that there is a “diminishing quark chemical potential toward the stellar surface, which renders the (negatively charged) strange quarks less abundant.” (So out goes my idea of strong coherence.) To maintain charge neutrality then electrons set up an outer sheet as part of a dipole layer. The further references are old or pay-walled, but I take it the quark matter state still applies, merely “less strange”. (&_&amp So the electrons could come from wherever, within a Debye length. Actually there is a further complication there, as “the increase in gravitational mass of strange stars, resulting from the energy associated with the electric dipole layer on the surface,… Read more »
Torbjorn Larsson OM
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Torbjorn Larsson OM
August 8, 2010 5:57 AM

“So the electrons could come from wherever, within a Debye length.”

Except that on further cogitation, if it is still quark matter, Steve’s description must then be correct; the bulk of these electrons must be part of the hydrogen to neutron to quark matter system in the first place.

DrFlimmer
Member
DrFlimmer
August 8, 2010 6:27 AM
@ Steve Nerlich So we agree. IIRC, I read somewhere that even “normal” neutron stars are surrounded by some kind of an atmosphere which is basically made up of iron nuclei and most likely enough electrons to keep charge neutrality. The question that follows then, of course, is how likely it is that the positive ions and the electrons build up a double layer with different rotational velocities. Maybe the preexisting magnetic field of the precursor star could play a role. Due to the compression of the star’s core into the neutron star the magnetic field strength has already grown by many orders of magnitude. I am not quite sure if this could aid the formation of a… Read more »
Lawrence B. Crowell
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Lawrence B. Crowell
August 8, 2010 6:45 AM
Strangelets caused a bit of a stir in the 1990s when the RHIC at Brookhaven came on line. This was echoed by later concerns of black holes being produced in the LHC, due to theories which connect extra dimensional physics at these energy scales with small quantum amplitudes for black hole or AdS physics. To start these concerns were never worth the worry. Cosmic rays at far higher energy slam into the Earth’s atmosphere, the moon, Mars, the sun and so forth. If these processes were the dominant or lower energy process then they would have already happened. If strangelets were the preferred state of quark matter, being the lower energy configuration, the universe at large would have… Read more »
Vanamonde
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Vanamonde
August 8, 2010 7:51 PM

Mr. Crowell! You are a treasure, sir and I hope you will bear me with this one. I have understood the Cosmic Rays are sooo much more powerful anyway to be a Very Good Argument against either the RHIC or LHC ending the world. But it is all about the Tev? What about luminosity? How does does the luminosity of our machines compare to the naturally occuring showers of Tev beasties?

Torbjorn Larsson OM
Member
Torbjorn Larsson OM
August 8, 2010 11:52 PM
even “normal” neutron stars are surrounded by some kind of an atmosphere which is basically made up of iron nuclei and most likely enough electrons to keep charge neutrality. That doesn’t explain the paper strange (negative charge) surface depletion though, you would need more electrons. But the quark matter conversion supply or deplete the majority of the electrons AFAIU. (LBC made it explicit.) [And I believe I misread Steve on this point. Oh, well.] @ LBC: Very pedagogic walk through, thanks! these concerns were never worth the worry. Cosmic rays at far higher energy slam into the Earth’s atmosphere, D’oh, I knew in returning I forgot to point out that the article lacked something. Thanks again, LBC! @… Read more »
Paul Eaton-Jones
Member
August 9, 2010 12:58 AM

Might the ‘excess’ of electrons at the surface be down to the fact that they a point-like objects with no interior structure whereas the neutrons are a 3-quark particle?As the neutrons become even more compressed they ‘release’ their electrons [becoming protons for a short time??] and the resulting protons and neutrons then ‘break down’ into their constituent quarks. Just a thought.

Lawrence B. Crowell
Member
Lawrence B. Crowell
August 9, 2010 5:56 AM
The occurrence of electrons is from channel or amplitude s – -> u + e. The strange quark has a charge –e/3 and the up quark is 2e/3. Under the extreme pressures in the centers of these compact objects the inverse process occurs. A neutron is a baryon quark triple (u,d,d), for the down quark charge –e/3. So in the quark-gluon plasma we may think of triplets of quarks are being “melted” neutrons (u,d,d) or metled Lambda^0 particle (u,d,s). The conversion of a triplet (u,d,d) to (u,d,s) results in no electron excess, but if there is a boundary layer in the star where three quarks at higher pressure are (u,d,s) then a slight reduction of pressure will result… Read more »
Torbjorn Larsson OM
Member
Torbjorn Larsson OM
August 9, 2010 8:24 AM

As the neutrons become even more compressed they ‘release’ their electrons [becoming protons for a short time??]

Um, yes, that would be the result it seems to me, and LBC seem to confirm this.

In any case there must be a free energy change for the quark/electron system, if one can interpret it as a “quark chemical potential” (see the quote from the paper). Pressure change (inherited from gravitational potential energy change) would indeed be the obvious culprit for the free energy change, but what do I know about bound quark systems? :-~

[Paywall references, let me enumerate all the ways I hate you … eh, better not, or we will be here indefinitely.]

Lawrence B. Crowell
Member
Lawrence B. Crowell
August 9, 2010 9:27 AM
The physics is in a three layer sandwich. With the left being close to the core a triplet of quarks are —(u,d,s)—|—(u,d,d)—|—(u,u,d)— 0 – – increasing radius – -> where on the far left is the “melt” or quark gluon plasma “triplet.” This triplet would construct a Lambda^0 hyperon by itself, but where the quark triple is shown here for ease of discussion. The middle layer is the neutron material layer. This layer I am somewhat aware of is itself rather complicated, but FAPP it is a gas or fluid of neutrons. Then there is the layer of degenerate iron as a crust, where the (u,u,d) indicates the presence of protons. So there are three boundary layers here.… Read more »
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