Neutron star fragmentation dynamics: Minimum fragment size

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astrobooger

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When a star collapses in on itself, and becomes a neutron star, it takes a lot of gravity. However, if 2 neutron stars collided at very high speeds (too high to merge together) they would fragment. <br /><br />The outer shell is composed primarily of iron nuclei. Inside, it is a liquid composed primarily of neutrons, with the composition of neutrons increasing as you get closer to the center. If the center was successfully fragmented, then superdense pieces of clumped up neutrons would fly into space. <br /><br />Because these pieces from the center would be pure superdense neutrons, would the fragments stay together in a superdense form, even with superficial gravity? After all, the neutrons will not repel one another, such as protons or electrons would.<br /><br />Basically, would the pure-neutron fragments stay in superdense form after fragmentation? And what would the minimum fragment size be?
 
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vogon13

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Your in a pretty esoteric realm there.<br /><br />I'll take a stab at it; the collision energies will increase the temperature of all the materials involved.<br /><br /> The neutronium materials rely on gravity for cohesion.<br /><br />You are increasing the temperature, and decreasing the cohesion (momentarily), so I don't think you get fragments. More of a spray emerges, and if there is any kind of resisting medium (not ruling out the combined gravitational field of the 2 merged objects, mind you) there won't be much material that will excape the impact.<br /><br /> I'll ponder this messy (but interesting) topic some more. There might be some aspects to this I haven't considered yet . . . . <br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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Saiph

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hmmm...tough question here.<br /><br />The core is degenerate, actually most of the star is. As such the temperature of the object does not increase when you pump energy into it. All that happens is you transform more and more of the material into a non-degenerate state.<br /><br />So, most of the star would no longer be degenerate, as that's where most of the impact energy went.<br /><br />However, if fragments survive, I've been told that there is no minimum mass for a white dwarf, or neutron star to remain as a degenerate compact object. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>
 
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search

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Hello astrobooger<br /> Neutron star<br /><br />The following was taken from sites below and compiled for the purpose of the post (read full articles):<br /><br />Collisionof 1.4MNeutronStars: Dynamical or Quasi-Equilibrium? <br /><br />Final Report for NASA CAN NCCS5-153<br />(See simulations)<br /><br />There is a conjecture put forth by S. Shapiro stating that for neutron stars colliding head-on in a free-fall from infinity, the merged object will be supported by the thermal pressure, and it will not collapse into a black hole before significant radiative cooling. This a delayed collapse, in contrast to a prompt collapse that happens on the dynamical time scale. Delayed and prompt collapses are drastically different: radiative cooling time scale is of order seconds, much longer than the dynamical timescale which is of order seconds. A delayed collapse will be spherical and generate much less gravitational wave. While for low mass neutron star collisions (in which the merged object is not much heavier than the critical TOV mass) one may not be surprised to see delayed collapse, the intriguing point is: The conjecture states that it will always be a delayed collapse independent of the masses of the initial neutron stars with any polytropic equation of state, where the polytropic coefficient is a function of entropy, and polytropic index is a space-time constant.<br /><br />There is a potential danger which could invalidate the argum
 
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search

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Regarding the dynamic of collision here is the important part:<br />EOS - Nuclear Equation of State<br />http://a.web.cern.ch/a/alicedoc/www/chic/Danielewicz1201.ps.gz<br /><br />Abstract. Nuclear equation of state plays an important role in the evolution of the Universe, in supernova explosions and, thus, in the production of heavy elements, and in stability of neutron stars. The equation constrains the two- and three-nucleon interactions and the quantum chromodynamics in nonperturbative regime. Despite the importance of the equation, though, its features had remained fairly obscure. The talk reviews new results on the equation of state from measurements of giant nuclear oscillations and from studies of particle emission in central collisions of heavy nuclei.<br /><br />From page 5 of the PDF above:<br />A possible site for the synthesis of heavy elements, other than supernova explosions, are mergers of neutron stars. These mergers shed much more matter into space if the nuclear EOS is relatively soft than when it is stiff, Fig. 10.<br />
 
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nexium

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Head on collisions of neutron stars are likely very, very rare = perhaps one per billion galaxies per billion years. Fragments are intuitive if the impact speed is 0.9 c. That fast however is also very, very rare, so the first fragmenting may still be in our future within the sphere with a radius of 12 billion light years of Earth.<br />If fragments retain nuetronium and/or white star stuff, long term in thier interior, we may find some very strange asteroids and comets, hundreds of kilometers in diameter, but with surface gravity several times that of Earth, and perhaps half the mass of Earth because 0.001% of the volume is compact matter. Unusually warm surface temperature is also likely. Neil
 
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search

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Very rare indeed I do not even know of any such observation. Just know of theoretical and simulation studies. <br /><br />However such events could occur in globular clusters where stars are closer to each other than anywhere else.
 
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SpeedFreek

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This is probably just me being too simplistic in approach, but if neutronium is only ever made in neutron stars, wouldn't a fragment of neutronium just become free neutrons when the gravitational contraints of the neutron star are removed?<br /><br />I.E. if you could somehow teleport a bucketful of neutronium from the inside of a neutron star into your laboratory, it would not be gravitationally compressed into the denegrate matter that defines it as neutronium any more. It would be free neutronium which would beta decay into protons and eventually just end up as hydrogen? <div class="Discussion_UserSignature"> <p><font color="#ff0000">_______________________________________________<br /></font><font size="2"><em>SpeedFreek</em></font> </p> </div>
 
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vogon13

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Transporting neutronium would be a rather dramatic way of destroying the Enterprise.<br /><br />The neutrronium would tend to expand violently.<br /><br />Very violently.<br /><br /><br />Extremely very violently.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>
 
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search

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Only you...fast finger.<br /><br />"You are saying there is the board with the target after I said where is the target"<br /><br />Off course since starburst is an event resulting from colliding galaxies and the collision of galaxies may create a globular cluster.<br /><br />Here is some wiki info for everybody:<br /><br />Definitions of starburst<br /><br />Several definitions of the term starburst galaxy exist and there isn't really a strict definition on which all astronomers agree. However, they would generally agree that the definition must in some way be related to (i) the rate at which the galaxy is currently converting gas into stars -- the star-formation rate (SFR) (ii) the available quantity of gas from which stars can be formed (iii) perhaps some additional timescales. Commonly used definitions include:<br /><br />Continued star-formation with the current SFR would exhaust the available gas reservoir in much less than the age of the Universe (the Hubble Time). This is sometimes referred to as a "true" starburst.<br /><br />Continued star-formation with the current SFR would exhaust the available gas reservoir in much less than the dynamical timescale of the galaxy (perhaps one rotation period in a disk type galaxy).<br /><br />The current SFR, normalised by the past-averaged SFR is much greater than unity. This ratio is referred to as the birthrate parameter.<br />[edit]Starburst triggering mechanisms<br /><br />Essentially to ignite a starburst, it is necessary to concentrate a lot of cool molecular gas in a small volume. Such concentrations and perturbations are strongly suspected to cause global starburst phenomena in major galaxy mergers, although the exact mechanisms are not fully understood. Observational surveys have long since shown that there is often a burst of disk star-formation in merging and interacting pairs of galaxies. It is also currently believed that nearby interactions between galaxies that don't actually merge can trigger unstable rotation modes, such
 
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michaelmozina

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http://arxiv.org/PS_cache/astro-ph/pdf/0201/0201434.pdf<br /><br />I believe that the minimum size for a decaying neutron star is presumed to be somewhere around .1 solar masses. I assume that would probably apply to "shards" or fragments, but they may have to be somewhat larger than the absolute minimum size to also survive an impact of some sort yet still remain stable. <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>
 
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search

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Attending is not the problem. The problem is understanding data.<br /><br />Starburst glaxies are an event galaxy originated by the collision (merger) between galaxies (all types of galaxies may collide/merge). When this event takes place a Globular Cluster may occur (A globular cluster is a spherical collection of stars that orbits a galactic core as a satellite). Because these are old stars the chance that you will have more supernovae and neutron stars increase.
 
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publiusr

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You might have some new elements. I think neutron stars still have carbon and oxygen in them, so a large cloud of CO2 might be a result, with some iron shards and perhaps some materials that wouldn't expand with all the elctrons out of them perhaps--or just some elements higher up the periodic table...who can really say?
 
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search

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"The Milky Way globular cluster M15 contains a double neutron star system, M15C, that will eventually spiral together and merge violently. Such mergers are a likely source of short gamma-ray bursts. Neutron star binaries are expected to form in globular clusters due to the likelihood of stellar exchanges in that crowded environment."<br />http://www.cfa.harvard.edu/press/pr0612image.html<br />http://cfa-www.harvard.edu/press/pr0612.html <br /><br />M82 and starburst galaxy formation and the subject where to look for Neutron stars collisions):<br /><br />M82 high level of star formation is due to a close encounter with the nearby spiral M81. Maps of the regions made with radio telescopes show large streams of neutral hydrogen connecting the two galaxies, also as a result of the encounter. Radio images of the central regions of M82 also show a large number of young supernova remnants, left behind when the more massive stars created in the starburst come to the end of their lives.<br /><br />Merging is "one of the processes" of creation of a starburst galaxy (see my post above or the link below)). And that is the one process I believe should be the focus point for neutron stars search. <br /><br />Not that starburst galaxies formed by other than merging process (link) will not be able to expose “head on” collisions between neutron stars but the chances probably are smaller.<br /><br />From 2005:<br />http://arxiv.org/abs/astro-ph/0512654<br />Short gamma-ray bursts from binary neutron star mergers in globular clusters<br />Abstract:<br />The first locations of short gamma-ray bursts (GRBs) in elliptical galaxies suggest they are produced by the mergers of double neutron star (DNS) binaries in old st
 
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