Page 1 of 2 12 LastLast
Results 1 to 30 of 37

Thread: neutron star and black hole?

  1. #1
    Join Date
    May 2005
    Posts
    1,810

    neutron star and black hole?

    I've been mulling around some ideas about categorization of bodies after a non-forum discussion about the internal structure of black holes. In particular, I was thinking about where the point of where escape velocity for a body reaches c, and whether that was possible for a star that has not collapsed beyond neutron degeneracy.

    In other words, could a neutron star be massive enough to have an event horizon?

  2. #2
    Join Date
    Jul 2005
    Location
    Massachusetts, USA
    Posts
    22,123
    Quote Originally Posted by baric View Post
    could a neutron star be massive enough to have an event horizon?
    Not for long. It would rapidly fall in through the rapidly expanding event horizon.
    Forming opinions as we speak

  3. #3
    Join Date
    May 2005
    Posts
    1,810
    Quote Originally Posted by antoniseb View Post
    Not for long. It would rapidly fall in through the rapidly expanding event horizon.
    fall in? The event horizon would be surrounding the star.

    My question is whether a neutron star can be massive enough to form an event horizon.

  4. #4
    Join Date
    Apr 2007
    Location
    Nowhere (middle)
    Posts
    38,011
    The term event horizon is a bit misleading. It doesn't refer to a physical location, but rather to a gravitational density. So, by definition, anything that has gravity which is enough to prevent light from escaping, is a black hole. The event horizon is the point of gravitational density at which that occurs.
    "I'm planning to live forever. So far, that's working perfectly." Steven Wright

  5. #5
    Join Date
    Jan 2006
    Posts
    1,816
    By definition, a BH cannot be made of neutrons, because no information can escape a black hole, and having it "made" of something would suggest that information about its compostion had escaped

  6. #6
    Join Date
    May 2005
    Posts
    1,810
    Quote Originally Posted by Noclevername View Post
    The term event horizon is a bit misleading. It doesn't refer to a physical location, but rather to a gravitational density. So, by definition, anything that has gravity which is enough to prevent light from escaping, is a black hole. The event horizon is the point of gravitational density at which that occurs.
    ? The event horizon is the calculated boundary in space around a massive object at which escape velocity is c.

    Anything that has an event horizon is most definitely a black hole, I agree with that completely. What I am asking is if the star at the center of the black hole (the one whose gravity is creating the event horizon) could possibly be a large neutron star, or must it always be something of a much greater density than neutron degeneracy can support?


    Quote Originally Posted by Peter Wilson
    By definition, a BH cannot be made of neutrons, because no information can escape a black hole, and having it "made" of something would suggest that information about its compostion had escaped.
    Well of course it's made of something, right? Otherwise there would be no mass to create the gravitational field. Solar masses don't just disappear when their neutrons collapse from pressure.

  7. #7
    Join Date
    Nov 2001
    Posts
    3,272
    Quote Originally Posted by baric View Post
    Well of course it's made of something, right? Otherwise there would be no mass to create the gravitational field. Solar masses don't just disappear when their neutrons collapse from pressure.
    That answer to that is basically ATM, as there is no way currently to prove other forms of degenerate matter.

    However past nuetron degeneracy, there are hypothosis' of quark degenerate matter, past that pion/gluon degenerate mater, past that string degenerate matter? and after there are really no good hypothosis'.

    Some super heavy nutron stars (magnatars), its also hypothisised, might have quark degenerate matter in thier cores.

  8. #8
    Join Date
    May 2005
    Posts
    1,810
    Quote Originally Posted by dgavin View Post
    Some super heavy nutron stars (magnatars), its also hypothisised, might have quark degenerate matter in thier cores.
    If that's the case, then it would answer my original post. If the pressure inside the most massive neutron stars is enough to overcome neutron degeneracy without forming an event horizon, then the answer would seem to be 'no'.

    I guess quark degenerate matter would be the next logical threshold. I wonder if degeneracy ever stops, or if it's turtles all the way down.

  9. #9
    Join Date
    May 2006
    Posts
    242
    Not N stars, but it seems they could form directly from huge clouds of gas (i.e. a huge cloud of air at STP that is massive enough to form an event horizon)... perhaps possible in the early universe?

  10. #10
    Join Date
    Aug 2003
    Location
    The Wild West
    Posts
    9,500
    Quote Originally Posted by baric View Post
    What I am asking is if the star at the center of the black hole (the one whose gravity is creating the event horizon) could possibly be a large neutron star, or must it always be something of a much greater density than neutron degeneracy can support?
    I believe neutron degeneracy pressure has a very specific value, and if there is not enough infalling mass to overcome that pressure gravitationally, the object stabilizes as a neutron star, the density of which is not enough to form an event horizon.

    Quote Originally Posted by baric
    In other words, could a neutron star be massive enough to have an event horizon?
    I'd say no. There's a pretty clear cut-off between the masses of white dwarfs, neutron stars, and black holes. And there are gaps where objects with intermediate masses are simply unstable. Check out Kip Thorne's Black Holes and Time Warps: Einstein's Outrageous Legacy.
    Everyone is entitled to his own opinion, but not his own facts.

  11. #11
    Join Date
    May 2005
    Posts
    1,810
    Thanks for all of the informative replies. They are definitely appreciated.

  12. #12
    Join Date
    Jan 2006
    Posts
    1,816

    Definite in late universe...

    Quote Originally Posted by yuzuha View Post
    Not N stars, but it seems they could form directly from huge clouds of gas (i.e. a huge cloud of air at STP that is massive enough to form an event horizon)... perhaps possible in the early universe?
    [my bold]

    We live inside a huge cloud of gas that has formed an event horizon 28 bly in diameter...


  13. #13
    Join Date
    Nov 2003
    Posts
    2,586
    A neutron star is equally as dense as a single neutron, right? So, if a single neutron is not a black hole, then a large ball of them wouldn't be either. However, as you stated:

    Quote Originally Posted by baric View Post
    I guess quark degenerate matter would be the next logical threshold
    Exactly. If you keep adding mass, at some point, the neutron star begins falling in on itself. It stops falling when it hits quarks, and now it is much denser, but no more dense than a quark. However:

    Quote Originally Posted by baric View Post
    I wonder if degeneracy ever stops, or if it's turtles all the way down.
    This is my understanding: eventually, you have a situation where it falls in on itself and just keeps falling until it's nothing - zero volume, a singularity. That singularity has an event horizon with radius greater than zero. When you drop addition mass into it, the singularity grows.

  14. #14
    Join Date
    Jun 2006
    Posts
    72
    So, is the point at which gravity is strong enough to form a singularity the precise point at which gravity is strong enough to form an event horizon? Or can an object have enough gravity to form into a singularity with out having enough gravity to form an event horizon, or be massive enough to form an event horizon without being massive enough to form into a singularity? And if so what are the supposed differences between these masses?

  15. #15
    Join Date
    Nov 2003
    Posts
    2,586
    So, is the point at which gravity is strong enough to form a singularity the precise point at which gravity is strong enough to form an event horizon?
    It doesn't have to be the precise point because once you're on your way to a singularity, you're moving - falling inward with nothing to stop you (except the cosmic speed limit). So even if there was a *huge* difference between the two, it would still mean that you always get a black hole.

    So a bad analogy might be, "is the point where you fall off a building (that is, the point where the building no longer supports you) the precise moment when you die?" It doesn't have to be. Once you're falling, you're on your way there. Is the point where neutron (or quark or whatever is the last form of) degeneracy fails the precise point where you become dense enough to have an event horizon? I dunno. It doesn't have to be though, because once you're falling, you're on your way to zero volume.

    Of course, if your total mass is very small then the black hole will evaporate instantly, but we're talking about stellar-mass black holes here I think.

  16. #16
    Join Date
    Jun 2010
    Posts
    13
    Quote Originally Posted by Peter Wilson View Post
    By definition, a BH cannot be made of neutrons, because no information can escape a black hole, and having it "made" of something would suggest that information about its compostion had escaped
    If you watch it become a BH, you've seen it's composition beforehand (before it starts hogging it's info).

  17. #17
    Join Date
    Mar 2004
    Posts
    13,440
    Quote Originally Posted by TheIvan View Post
    If you watch it become a BH, you've seen it's composition beforehand (before it starts hogging it's info).
    Doesn't help much ... by its nature, you have no way of knowing what happened to the matter (and energy) that crossed the event horizon (other than that spin, charge, and mass-energy are conserved).

  18. #18
    Join Date
    May 2007
    Location
    Earth
    Posts
    10,326
    Just to confuse the issue, I did some algebra.

    My assumptions are simply Newtonian gravity.

    v=sqrt((8/3) π G ρ R2)
    Just plug in the appropriate numbers.

    I plugged in a few, based on v = c = 300,000,000 m s-1 and ρ = 0.001 kg m-3

    and got a value for the radius of the event horizon of about 4e14 m, or (if my conversion is vaguely correct) about 23.5 light-years.

    In other words, one can have a black hole without going to extreme states of matter. Of course, a black hole with a 23.5 light-year event horizon would mass about 2e56 kg or about 1026 solar masses, or about 5e9 times the mass of the Milky Way.

    Now, I just hope my algebra was vaguely correct
    Information about American English usage here. Floating point issues? Please read this before posting.

    How do things fly? This explains it all.

    Actually they can't: "Heavier-than-air flying machines are impossible." - Lord Kelvin, president, Royal Society, 1895.



  19. #19
    Join Date
    May 2005
    Posts
    1,810
    This thread is such a letdown! I saw "neutron star or black hole?" for the topic and thought, "OMG! a discussion I'm really interested in!"

    Then I realize it's a resurrected thread that I started years ago and was already answered!

    Curses!

  20. #20
    Join Date
    May 2003
    Location
    of Greatest Eclipse, Aug. 21 2017 (Kentucky, USA)
    Posts
    4,552
    Quote Originally Posted by swampyankee View Post
    Just to confuse the issue, I did some algebra.

    My assumptions are simply Newtonian gravity.

    v=sqrt((8/3) π G ρ R2)
    Just plug in the appropriate numbers.

    I plugged in a few, based on v = c = 300,000,000 m s-1 and ρ = 0.001 kg m-3

    and got a value for the radius of the event horizon of about 4e14 m, or (if my conversion is vaguely correct) about 23.5 light-years.

    In other words, one can have a black hole without going to extreme states of matter. Of course, a black hole with a 23.5 light-year event horizon would mass about 2e56 kg or about 1026 solar masses, or about 5e9 times the mass of the Milky Way.

    Now, I just hope my algebra was vaguely correct
    You've also assumed a uniform density within your 6e43 kg mass. (That's the mass of 30 trillion Suns, btw.) Your algebra may be correct, but your physics is pushing it a little.

  21. #21
    Join Date
    Aug 2003
    Location
    The Wild West
    Posts
    9,500
    Quote Originally Posted by Cougar View Post
    I believe neutron degeneracy pressure has a very specific value, and if there is not enough infalling mass to overcome that pressure gravitationally, the object stabilizes as a neutron star, the density of which is not enough to form an event horizon.
    A neutron star is still pretty dense. Like the density of the entire human population of the planet compressed into the volume of a sugar cube.
    Everyone is entitled to his own opinion, but not his own facts.

  22. #22
    Join Date
    Jun 2007
    Posts
    1,956
    Quote Originally Posted by Peter Wilson View Post
    By definition, a BH cannot be made of neutrons, because no information can escape a black hole, and having it "made" of something would suggest that information about its compostion had escaped


    If you define something to be a toy model does that make it a toy model?

    There is currently no model that explains the observation of pulsars and magtars.

    As the compact object get larger why is everyone so confident it forms a classic BH?

    A classic BH is a toy model. A theoretical mathematical object.

  23. #23
    Join Date
    Jun 2007
    Posts
    1,956
    http://arxiv.org/PS_cache/astro-ph/p.../0308347v1.pdf


    This paper was included as recommended reading at a presentation made at a pulsar conference for specialists in that field.

    F. C. Michel alleges that due to more sophisticated earth and space based telescopes there is now sufficient observational evidence to make progress in pulsar theory. Michel alleges in this paper that one obstacle to advancement in pulsar astrophysics is that specific theoretical models when they are included in text books and taught fix the thinking concerning this subject. Michel alleges that observational evidence and holistic critical fundamental physical analysis of the text book models in question shows that they are fundamentally incorrect.

    Michel's point is there was no rational reason to present the pulsar textbook model as the correct model. The class of pulsar model that he alleges may lead to a solution was postulated in the 1960s.


    The State of Pulsar Theory
    However, recent theoretical work is converging on a picture that closely resembles the latest HST and CHANDRA images, providing hope for the future. No less than 3 groups have recently confirmed the early Krause-Polstorff-Michel simulations showing that the fundamental plasma distribution around a rotating neutron star consists of two polar domes and an equatorial torus of trapped nonneutral plasma of opposite sign charges. Unless a lot of new physics can be added, this distribution renders the Goldreich-Julian model irrelevant (i.e., along with most of the theoretical publications over the last 33 years).

    So 35 years have passed. Will the way pulsars work yield to theory alone? Will it yield to observation alone? The numbers are not on anyone’s side. I will try to suggest why theory hasn’t done it yet. One reason was the chaotic approach to the problem, everyone running in different directions. The other is, paradoxically, how a strong line of conventional wisdom keeps people from looking in different directions, which we will next examine.
    Pair production
    The possible role of pair production has been an interesting one, and we find it very attractive (Michel 1991b) because it could explain how charged bunches would form naturally and thereby account for the coherency of pulsar radiation. One role of pair production might be to provide ionization outside of the neutron star and thereby help “fill” the magnetosphere as imagined in the GJ model (although these authors were clear in their assumption that the magnetospheric particles all came from the surface). Although something like this should be possible (owing to the huge E* B ≠ 0 regions between the domes and the tori) STM (2001) show that the consequent filling of the domes and tori reduce this source and would turn it off. Moreover, for typical pulsars where the magnetic field at the famous light cylinder would be only of the order of a few gauss, pair production would have no chance of operating. Pair production was suggested in the first place only because the pulsar magnetic fields were so large at the surface.
    Nonneutral Plasmas
    Most astrophysicists or physicists are not taught nonneutral plasmas. There are relatively few sources Davidson (1990), Michel and Li (1999), Michel (1982, 1991a). Yet nonneutral plasmas are the natural plasmas to be found around strongly electrified objects like rotating neutron stars, simply because the huge electric fields tend to stratify the plasma (as in producing domes and tori) and selectively pull out plasma (from conducting surfaces) of only one sign. The fact that the plasma surrounding a rotating magnetized neutron star should be arranged in the form of domes and tori should be understood as a fundamental one which would have to be explicitly modified if one were to find a structurally different configurations (such as accelerating gaps over the polar caps) instead of simply being ignored because it doesn’t fit preconception.
    Danger when theorists start looking at the same page
    Theorists seem uninterested in why 35 years have passed with so little success. Not even interested enough when it can be shown that the favorite model is a cartoon model not based on real physics. The possible bad news here is that a number of other people have now become interested in how nonneutral plasmas impact our understanding of pulsars. Then everyone might have to learn this stuff!

  24. #24
    Join Date
    Mar 2004
    Posts
    13,440
    Quote Originally Posted by William View Post
    http://arxiv.org/PS_cache/astro-ph/p.../0308347v1.pdf


    This paper was included as recommended reading at a presentation made at a pulsar conference for specialists in that field.

    F. C. Michel alleges that due to more sophisticated earth and space based telescopes there is now sufficient observational evidence to make progress in pulsar theory. Michel alleges in this paper that one obstacle to advancement in pulsar astrophysics is that specific theoretical models when they are included in text books and taught fix the thinking concerning this subject. Michel alleges that observational evidence and holistic critical fundamental physical analysis of the text book models in question shows that they are fundamentally incorrect.

    Michel's point is there was no rational reason to present the pulsar textbook model as the correct model. The class of pulsar model that he alleges may lead to a solution was postulated in the 1960s.
    That's a 2003 preprint, later published in a 2004 book, based on a 2002 conference presentation.

    Quite a lot has happened since then ... as you can readily see by looking just the 17 papers which cite the Michel one.

    Interestingly, only one of those 17 is by Michel himself, and since then he has published only 6 papers (that I could find), only three of which have to do with pulsars.

    William, can you give us a concise summary of how this field of research has developed, since 2003?

  25. #25
    Join Date
    Jun 2007
    Posts
    1,956
    Typically theories would compete based on observational evidence. There would be pro/cons for the different theories. If there is no observational evidence to decide either theory could be correct.

    There is confirmation massive objects exist. That does not confirm they have an hard surface and an event horizon.

    The observational evidence seems to support the assertion that massive objects do not form a classical BH complete with an event horizon. (For example the x-rays that observed in vicinity of the Milky Way's BH is roughly 10 to 100,000 times less than what theory predicts based on the observations of the amount of gas that should be in falling into the BH.


    http://journalofcosmology.com/RobetsonLeiter.pdf



    Does Sgr A* Have an Event Horizon or a Magnetic Moment?


    In this work we extend the general relativistic Magnetospheric Eternally Collapsing Object (MECO) model for application to Sgr A*. In a series of papers published within the last few years, it has been shown that the MECO model has been able to account for all of the observational phenomena associated with the galactic black hole candidates (GBHC) and more luminous active galactic nuclei (AGN). For a given mass, the MECO is characterized by only two mass scaled parameters; surface magnetic field strength and rotation rate. Without changing either of these parameters previously found for GBHC and AGN, we demonstrate that the MECO model for Sgr A*: a) satisfies all of the luminosity constraints that have previously been claimed as proof of an event horizon, b) reconciles the low bolometric luminosity of Sgr A* with its expected Bondi accretion rate by means of a magnetic propeller driven outow, c) accounts for the Sgr A* NIR and X-ray luminosities, the general characteristics of its broad band spectrum, and the temporal sequence of ares in different spectral ranges as well as the pattern of its observed orthogonal radio and NIR polarizations. High resolution radio images of a MECO would be produced in an equatorial OUTFLOW, while high resolution images in NIR wavelengths would be elongated along two INFLOWS into the magnetic poles (apparently generally N-S). These patterns would be distinguishable from black hole RIAF models for which all emissions would arise from an accretion disk. Combination black hole disk-jet models for which the NIR originated in a disk viewed at high inclination would also be distinguished by showing only unidirectional …
    Eternally Collapsing Object


    http://www.scitopics.com/Eternally_C...ng_Object.html

    http://arxiv.org/PS_cache/astro-ph/p.../0510162v4.pdf
    On the Non-occurrence of Type I X-ray Bursts from the Black Hole Candidates

    It has been justifiably questioned that if the Black Hole Candidates (BHCs) have a “hard surface” why Type I X-ray bursts are not seen from them (Nayayan, R., Black Holes in Astrophysics, New J. Phys., 7, 199-218, 2005). It is pointed out that a “physical surface” need not always be “hard” and in could be “gaseous” in case the compact object is sufficiently hot (Mitra, A., The day of reckoning: the value of the integration constant in the vacuum Schwarzschild solution, physics/0504076, p1- p6; BHs or Eternally Collapsing Objects: A review of 90 years of misconceptions, in Focus on Black Hole Research, Nova Sc. Pub., NY, p1-p94, 2006).

    Even if a “hard surface” would be there, presence of strong strong intrinsic magnetic field could inhibit Type I X-ray burst from a compact object as is the case for Her X-1. Thus, non-occurrence of Type I bursts actually rules out those alternatives of BHs which are either non-magnetized or cold and, hence, is no evidence for existence of Event Horizons (EHs). On the other hand, from the first principle, we again show that the BHCs being uncharged and having finite masses cannot be BHs, because uncharged BHs have a unique mass M = 0. Thus the previous results that the so called BHCs are actually extremely hot, ultramagnetized, Magnetospheric Eternally Collapsing Objects (ECOs) ( Robertson, S. & Leiter, D., Astrophys. J. 565, 447-451, 2002; MECO Model of galactic BH Candidates and active galactic nuclei, in: New Developments in BLack Hole Research, NOva Sc. Pub., NY, p1-p44, 2006) rather than anything else get reconfirmed by non-occurrence of Type I X-ray bursts in BHCs.

  26. #26
    Join Date
    Mar 2004
    Posts
    13,440
    Quote Originally Posted by William View Post
    If you define something to be a toy model does that make it a toy model?

    There is currently no model that explains the observation of pulsars and magtars.
    I'm pretty sure you don't mean what you have just written (and I'm referring to more than just the misspelling).

    Observationally, what is a magnetar?

    What observations of pulsars are, today, not explained by any model?

    As the compact object get larger why is everyone so confident it forms a classic BH?
    Because of the substantial difference between loss-mass and high-mass x-ray binaries?

    Because SgrA* has not been successfully modelled by anything other than a SMBH?

    And so on.

    A classic BH is a toy model. A theoretical mathematical object.
    What sort of model is there, in astrophysics, other than a "theoretical mathematical object"?

  27. #27
    Join Date
    Mar 2004
    Posts
    13,440
    Quote Originally Posted by William View Post
    Typically theories would compete based on observational evidence. There would be pro/cons for the different theories. If there is no observational evidence to decide either theory could be correct.

    There is confirmation massive objects exist. That does not confirm they have an hard surface and an event horizon.

    The observational evidence seems to support the assertion that massive objects do not form a classical BH complete with an event horizon. (For example the x-rays that observed in vicinity of the Milky Way's BH is roughly 10 to 100,000 times less than what theory predicts based on the observations of the amount of gas that should be in falling into the BH.


    http://journalofcosmology.com/RobetsonLeiter.pdf




    Eternally Collapsing Object


    http://www.scitopics.com/Eternally_C...ng_Object.html

    http://arxiv.org/PS_cache/astro-ph/p.../0510162v4.pdf
    First, the Journal of Cosmology is not a particularly good source, in astrophysics.

    Second, MECO (and ECO) are not "generally accepted scientific mainstream", to quote from the new Q&A policy (WP has a brief summary).

    Third, the expected x-ray luminosity of SgrA* is extremely difficult to model, for reasons that have little to do with the nature of black holes, in GR.

    Fourth, again, you do not seem to be writing what you intend to mean (e.g. "There is confirmation massive objects exist" - I think you missed a key qualifier, "compact").

  28. #28
    Join Date
    Jun 2007
    Posts
    1,956
    Nereid,
    Perhaps if you quoted a paper that has observational evidence that supports whatever view you have I would have something to reply to. There is an underlying tone to your comments which does not make logical sense to me. I do not understand the emotional response.

    i.e. If there is no observational evidence why are you so certain one hypothesis is correct? In my opinion it is not appropriate to censor scientific views from published papers. I read papers from both sides of the issues and think about the topic.

    In science there are often periods of times when three or four different theories compete. That is the nature of science.

    As others have said, it is an egregious error to pick one theory as the best or the correct theory when there is no observational evidence to select. The discussion concerns astronomical objects with extreme physics. The first models were guesses.

    This is in reply to your comment concerning pulsars and magtars. I believe your concern was the date of the paper. This paper was presented as the introduction to a 2008 conference on the Origin and Evolution of Neutron Star Magnetic Fields. The paper I quoted above was suggested reading by the review paper.

    As the author of the review paper "Origin and Evolution of Neutron Star Magnetic Fields" notes there needs to be observational data to select models.

    We know from observational data, pulsar and magtars have strong magnetic fields associated with them. What creates those strong magnetic fields?

    A classical BH has no hair and is not capable of generating a massive magnetic field. That is the point of my above comment. Observational evidence must be provided to support the assertion that the massive physical object is a classical BH. One cannot by definition make A = B where B is a physical object and A is a theoretical model.

    The source of the massive magnetic field in neutron stars and magtars is not known.

    http://arxiv.org/PS_cache/astro-ph/p.../0307133v1.pdf

    Origin and Evolution of Neutron Star Magnetic Fields

    Given its role in opening the International Workshop on Strong Magnetic Fields and Neutron Stars, this presentation has the purpose of giving a general overview about what is currently known about neutron star magnetic fields, their origin and evolution. Inevitably, it will contain much of the same material presented by the author in similar reviews in previous years (e.g., Reisenegger 2001a), of which it should be regarded to be an extension and update.

    Magnetic fields are most likely the main form of “hair” that allows neutron stars, contrary to black holes, to be distinguished from each other and classified into phenomenologically very different groups. Among single (or non-accreting binary) neutron stars, we distinguish “classical” pulsars, millisecond pulsars, soft gamma-ray repeaters, anomalous X-ray pulsars, and inactive, thermal X-ray emitters (see, e.g., Becker & Pavlov 2002). Binary systems with mass transfer onto a neutron star can be divided into high-mass and low-mass X-ray binaries (according to the companion mass), with substantially different properties. Magnetic fields play an essential role by accelerating particles, by channeling these particles or accretion flows, by producing synchrotron emission or resonant cyclotron scattering, and by providing the main mechanism for angular momentum loss from non-accreting stars. Moreover, evidence is mounting that soft gamma-ray repeaters and anomalous XAReisenegger1ray pulsars are really only slightly distinct types of very strongly magnetized neutron stars (“magnetars”) in which the magnetic field is the main energy source for the observed radiation

    On the other hand, we actually know surprisingly little about neutron star magnetic fields. In particular, most “measurements” of neutron star magnetic fields are indirect inferences, which are put in doubt both by their inconsistency with other observational evidence and with plausible theoretical models for the physics of their surroundings. Even less is known about the geometry of the magnetic field, its evolution, and its origin, so there is open space for speculation, modelling, and (hopefully) prediction of measurable effects that might test the theoretical ideas.

    2.3 Magnetars
    Two intriguing kinds of astronomical objects have in recent years found a likely interpretation as very highly magnetized neutron stars (see Thompson 2000 for a review; Kouveliotou et al. 2003 for a popular account)

    Perhaps most importantly, the persistent X-ray luminosity of these objects is much larger than their inferred spin-down power. Therefore, unlike the case of radio pulsars, rotation can not be a significant energy source. It has long been suggested that magnetic energy may be the ultimate source of both the bursts and the persistent radiation (Duncan & Thompson 1992; Paczynski 1992; Thompson & Duncan 1995, 1996), but this would still require a total magnetic energy significantly larger than inferred from the dipole field, i.e., a buried and/or disordered magnetic flux. In any case, the strong magnetic field may modify the radiation transport in the surface layers, so that these objects radiate a much larger fraction of their fossil heat in X-rays.

  29. #29
    Join Date
    Mar 2004
    Posts
    13,440
    William, I am have a lot of difficulty understanding what you write, and it's not just the odd missing or mis-spelled word.

    For example: "There is currently no model that explains the observation of pulsars and magtars."

    Now AFAIK, "magnetars" are hypothetical entities (theoretical models) which were developed precisely in order to explain various observations. The term was not developed solely on the basis of various observations, the way the "AGN" (active galactic nucleus) was (for example).

    So your simple sentence seems, to me, to make no sense at all (at least the part that refers to "magtars").

    Hence my question.

    It gets better.

    The section of the arXiv preprint you quote in your last post makes it clear that "magnetar" refers to a model ("interpretation") developed precisely to "explain" (your term) astronomical observations!

    And that's just the second sentence of the first of your recent posts in this thread!

    How about you slow down, and explain what you mean, clearly?

  30. #30
    Join Date
    Jun 2007
    Posts
    1,956
    Quote Originally Posted by William View Post
    Nereid,
    Perhaps if you quoted a paper that has observational evidence that supports whatever view you have I would have something to reply to. There is an underlying tone to your comments which does not make logical sense to me. I do not understand the emotional response.

    i.e. If there is no observational evidence why are you so certain one hypothesis is correct? In my opinion it is not appropriate to censor scientific views from published papers. I read papers from both sides of the issues and think about the topic.

    In science there are often periods of times when three or four different theories compete. That is the nature of science.

    As others have said, it is an egregious error to pick one theory as the best or the correct theory when there is no observational evidence to select. The discussion concerns astronomical objects with extreme physics. The first models were guesses.

    This is in reply to your comment concerning pulsars and magtars. I believe your concern was the date of the paper. This paper was presented as the introduction to a 2008 conference on the Origin and Evolution of Neutron Star Magnetic Fields. The paper I quoted above was suggested reading by the review paper.

    As the author of the review paper "Origin and Evolution of Neutron Star Magnetic Fields" notes there needs to be observational data to select models.

    We know from observational data, pulsar and magtars have strong magnetic fields associated with them. What creates those strong magnetic fields?

    A classical BH has no hair and is not capable of generating a massive magnetic field. That is the point of my above comment. Observational evidence must be provided to support the assertion that the massive physical object is a classical BH. One cannot by definition make A = B where B is a physical object and A is a theoretical model.

    The source of the massive magnetic field in neutron stars and magtars is not known.

    http://arxiv.org/PS_cache/astro-ph/p.../0307133v1.pdf
    Hi Nereid,

    I thought I would quote my comment. I did not understand your paraphrase. I have two quite specific points.

    This is a developing field there are many issues which are not resolved. When I quoted the review paper from 2008 the author noted the same review was used year after year as there were many fundamental unanswered questions. (including what creates the massive magnetic field in the compact objects).

    "Origin and Evolution of Neutron Star Magnetic Fields"

    Given its role in opening the International Workshop on Strong Magnetic Fields and Neutron Stars, this presentation has the purpose of giving a general overview about what is currently known about neutron star magnetic fields, their origin and evolution. Inevitably, it will contain much of the same material presented by the author in similar reviews in previous years (e.g., Reisenegger 2001a), of which it should be regarded to be an extension and update.
    On the other hand, we actually know surprisingly little about neutron star magnetic fields. In particular, most “measurements” of neutron star magnetic fields are indirect inferences, which are put in doubt both by their inconsistency with other observational evidence and with plausible theoretical models for the physics of their surroundings. Even less is known about the geometry of the magnetic field, its evolution, and its origin, so there is open space for speculation, modelling, and (hopefully) prediction of measurable effects that might test the theoretical ideas.
    http://arxiv.org/PS_cache/astro-ph/p.../0307133v1.pdf

    William said: We know from observational data, pulsar and magtars have strong magnetic fields associated with them. What creates those strong magnetic fields?
    William said: The source of the massive magnetic field in neutron stars and magtars is not known

    A classical BH has no hair and is not capable of generating a massive magnetic field. That is the point of my above comment. Observational evidence must be provided to support the assertion that the massive physical object is a classical BH. One cannot by definition make A = B where B is a physical object and A is a theoretical model.
    There are a dozens of published papers concerning the ECO/MECO theory. The authors of the ECO and MECO papers are specialists in their field (theoretical physics and astrophysics). They have published papers in books that are written for specialists in those fields (theoretical physics and astrophysics).

    My second point is that the ECO/MECO theory is a valid mainstream theory. We do not know which theory is correct (ECO/MECO Vs Classical BH). I believe it not appropriate to censor a theory or to select a theory for non scientific reasons.

    An attempt to censor makes every thread confrontational rather than a discussion with people who are interested in a general subject, who enjoy discussing mainstream theories, and the related observations. The tone should be pros/cons of one theory over the other, as if we are watching/discussing a sporting match series and do not know the outcome.

    I see in the forum someone started a thread on M-Theory, which I suppose is also a valid mainstream theory, however, the ECO and MECO authors have observational evidence to support their theory. The ECO and MECO theories make predictions.

Similar Threads

  1. Black hole or neutron star bending light
    By Copernicus in forum Space/Astronomy Questions and Answers
    Replies: 4
    Last Post: 2011-Jul-14, 05:22 AM
  2. Friction of a neutron star being sucked into a black hole
    By TheIvan in forum Space/Astronomy Questions and Answers
    Replies: 19
    Last Post: 2010-Jul-03, 04:44 PM
  3. That Neutron Star Should Be a Black Hole
    By Fraser in forum Universe Today
    Replies: 4
    Last Post: 2006-Apr-17, 02:05 PM
  4. Black Hole Gulps Down a Neutron Star
    By Fraser in forum Universe Today
    Replies: 3
    Last Post: 2005-Dec-17, 01:03 AM
  5. Black hole swallows a neutron star
    By Kullat Nunu in forum Astronomy
    Replies: 3
    Last Post: 2005-Dec-16, 06:51 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •