Talk:Neutron star/Archive 1

message: Do black holes exits at the center of neutron stars? Read something to that affect on a cosmology blog. Don't know if it's true or not though.
: That would not be possible, the star would destroy itself if there was a blackhole inside of it, as nothing can escape it. Real small blackholes can only be created if their matter is subjected to sufficient pressure from some source other than self-gravitation. Only a Primordial black hole or Micro black hole fit this description, but there is no proof for their existence. Even if they are possible, they would be verry unstable, evaporating verry fast. Patrick1982 22:49, 28 February 2007 (UTC)
thread_title: Black Holes

message: For the escape velocity of the neutron star, I wonder, was that found by using the traditional newtonian physics equation for gravitational potential energy, converting it into kinetic energy and finding the escape velocity? [ sqrt((2GM)/r) ] However, as it says, 150,000 km/s is half the speed of light, wouldn't you have to use general relativity to figure it out instead? Mercury has a much lower speed, yet even its orbit has certain relativistic effects. Are there any math geniuses that can confirm or refute the escape velocity of 150,000 km/s? It isn't important but it's sort of interesting to think about and I'd like to know. —The preceding unsigned comment was added by 72.59.2.127 (talk • contribs) .
:I may be wrong about this, but under the escape velocity section it implies that an object falling into a neutron star would necesarily impact it at a velocity equal to the escape velocity. I don't see why this is true at all. The velocity of anything impacting the star would be dependent on a variety of factors, including other gravitational forces in the area, and distance from the neutron star when the object began "falling" towards it. As written it implies that if two objects were orbiting the star, one at 1 AU and one at 1.5 AU, and they both stopped their orbits and began falling, they would both impact at the same final velocity. This appears plainly false. If I am messing up my physics someone let me know, but otherwise, I'm going to change it. Not my leg 20:07, 8 June 2006 (UTC)
replies: text: For all practical purposes, it's correct. While the impact velocity is only exactly equal to the escape velocity when the object is dropped from an arbitrarily far distance away, in practice, as long as the object is outside most of the potential well of the neutron star (in this case, more than a few hundred kilometres away), the difference in velocity is very small compared to the final velocity itself. --Christopher Thomas 20:56, 8 June 2006 (UTC)
thread_title: Escape Velocity

message: From the article:
:"When neutron stars were first discovered, they were believed to be evidence of extra-terrestrial intelligences. Because of their highly regular pattern of emmisions, they were initially though to be beacons of some type."
I don't think that pulsars were ever seriously thought to be evidence of extraterrestrial intelligence, at least not by the researchers who were actually investigating them. The first pulsar discovered was dubbed "BEM-1" (Bug-Eyed Monster 1) as a joke by its discoverers, if I recall correctly. But since this is all from memory, anyone have any references handy? Bryan Derksen
:Actually it was called LGM-1 (little green men).  According to the article pulsar they did seriously consider it.  The reference used is astrophysicist Perer Sturrock but with his interest in UFOs I don't know how reliable the reference is. 
:An interesting article can be found here  which I was directed to from a NASA site.  It is a description of the discovery by Jocelyn Bell Burnell herself.  Of note is the passage that reads
::"In the paper to NATURE we mentioned that at one stage we had thought the signals might be from another civilization. When the paper was published the press descended, and when they discovered a woman was involved they descended even faster. I had my photograph taken standing on a bank, sitting on a bank, standing on a bank examining bogus records, sitting on a bank examining bogus records: one of them even had me running down the bank waving my arms in the air - Look happy dear, you've just made a Discovery! (Archimedes doesn't know what he missed!) Meanwhile the journalists were asking relevant questions like was I taller than or not quite as tall as Princess Margaret (we have quaint units of measurement in Britain) and how many boyfriends did I have at a time?"  Unmasked 01:55, 30 October 2006 (UTC)
thread_title: Extraterrestrials

message: The article specifies slow down rates that appear far, far too small (10-12 and 10-19 second for each century), in fact too small to logically produce the older slower-rotating stars within the universe's current age the article also mentions.
Googling around, I see zebu.uoregon.edu has "about 10-15 seconds per rotation", so I suspect "per century" should be changed to "per rotation", and this would change the next sentence as follows, for a star initially rotating at 1 second:
In other words, a neutron star now rotating in 1 second will rotate in 1.000003 seconds after a century, or 1.03 seconds after 1 million years.
Does this look sensible? -Wikibob | Talk 22:49, 2005 Apr 19 (UTC)
: This is kind of true, however generally the spin-down rate (period derivative) is expressed in dimensionless units, or if you want to think of it that way, seconds per second (=rotations per rotation). What you've said is kind of true since most observable neutron stars have rotation periods of the order of 1 second. However, on that point, both the spin period AND the period derivative are very much dependent on the type of neutron star (i.e. its history and present circumstances). So probably the whole paragraph needs to be generalised a bit, and the specific numbers and info left to the appropriate sub-articles. Rotation-powered pulsars spin down via magnetic dipole radiation, so their spin down rate depends on their magnetic field strength. The range you quoted is roughly valid for ordinary rotation powered pulsars, which have periods of mainly about 0.1-5 seconds. Recycled rotation powered pulsars otoh have periods of 1-100 milliseconds and spin down rates of 10-21 - -17, while magnetars have periods around 10 seconds spin down of 10-12 - -10. Accreting neutron stars OTOH vary in spin period due to the transfer of angular momentum from the accretion stream, so this can be spinning up or down and can vary with time, and have spin periods up to many 10s of seconds.  All this is IMO too much detail for the top level neutron star entry (but I don't have time at the moment to improve it myself). Rkundalini 07:07, 21 Apr 2005 (UTC)
thread_title:  Rate of rotation slow down? 

message: The Neutron star article states:
"Another class of neutron star, known as the magnetar, exists. These have a magnetic field of above 10 gigateslas, strong enough to wipe a credit card from the distance of the Sun and strong enough to be fatal from the distance of the Moon. By comparison, Earth's natural magnetic field is 50 microteslas, and on Earth a fatal magnetic field is only a theoretical possibility; some of the strongest fields generated are actually used in medical imaging. A small neodymium based rare earth magnet has a field of about a tesla, and most media used for data storage can be erased with milliteslas."
The Magnetar article states:
"A magnetic field above 10 gigateslas is strong enough to wipe a credit card from half the distance of the Moon from the Earth1. A small neodymium based rare earth magnet has a field of about a tesla, Earth has a geomagnetic field of 30-60 microteslas, and most media used for data storage can be erased with a millitesla field.
The magnetic field of a magnetar would be lethal at a distance of up to 1000 km, by warping the atoms in living flesh2."
The two don't agree too well, though they are clearly derived from similar source material. Maybe someone who knows which version is correct can fix the incorrect one? Thanks!--Ailicec 01:18, 7 Jun 2005 (UTC)
replies: text: Wouldn't the iron in your blood be affected, Xmen style, before the "atoms in living flesh" were warped? If that statment is untrue it would detract from the credibility of the 1000km statement. Rmrfstar 21:30, 19 May 2005 (UTC)
replies: text: The main point being that at least one of them is wrong. ((btw, added my sig to original question, I didn't know how to do it when I wrote that) --Ailicec 01:18, 7 Jun 2005 (UTC)
thread_title:  Effects of superstrong magnetic fields 

message: Early in the article: 
"Neutron stars have a mass of the same order as the mass of the Sun. Their size (radius) is of order 10 km, about 70,000 times smaller than the Sun."
Later in the redundant 5th paragraph:
"Neutron stars are typically about 20 km in diameter, have greater than 1.4 times the mass of our Sun"
This site:1 says it's 10km
But this one:2 says it must be at least 18km
Merick June 29, 2005 15:52 (UTC)
:The article says 20 km in diameter this is an accurate figure the 10km from the first link you posted is an estimate of the radius of a neutron star, that is normally taken to be around 10km.Allywilson 17:55, 14 March 2007 (UTC)
replies: text:  In astronomy, more important that actual figures are orders of magnitude. 10 km or 20 km, for an astronomer, is the same thing. I'm an astronomer, I can say that.  --Gspinoza 16:06, 20 March 2007 (UTC)
thread_title:  Size and mass? 

message: Is it known why some neutron stars are pulsars and some aren't? Or are they all, and it just isn't observable?
Response:
If I may, there are several models of static neutron stars (non rotating) which are still used to date to model parameters, which would not be considered 'pulsars', since any received beam of radio waves wouldn't 'pulse'. I suppose the question is  -  will a neutron star emit the radio waves if it isn't rotating?
One of the main advantages of pulsars is that they can be detected via these pulses. Neutron stars are otherwise very small, very dark, and extremely hard to find.
-- JDC
:Neutron stars can also be detected if there is nearby matter. The strong gravity of the star accretes the matter providing a large amount of kinetic energy causing it to get very hot and glows brightly. This can be seen in many neutron stars such as the Crab Pulsar which glows strongly in the x-ray and radio range of the spectrum. There is no current model for non-rotating neutron stars to be emitting pulses all current models (Magnetars, Accretion-powered pulsars and Rotation-powered pulsars) rely on the neutron star spinning. I have actually rethought this and am wondering if the star was recieveing energy for example by accretion is that not likely to exert a torque causing a non-rotating star to rotate. Infact can a neutron star ever stop spinning, they all have to start off spinning can they stop? Allywilson 18:14, 14 March 2007 (UTC)
thread_title:  Why are some pulsars? 

message: Concerning Fxer's new introduction, I'm ambivilant about keeping it. The new intro is less of a definition and is slower to give a clear idea of what a neutron star is and its importance (first theororized astromical object). For instance, that new sentence of the "weight" of a spoonful of a neutron star: Is that the kind of statistic we want in the intro paragraph? Also there is now presented irrelevant information on black holes and white dwarfs, which should be mentioned later... On a more positive note, the newer introduction correctly names Neutron stars as types of degenerate stars. Any other thoughts? -- Rmrfstar 00:17, 21 July 2005 (UTC)
replies: text: I'd be all for a rewritten version of the intro :) It was rewritten partially, and only confused things more, so I changed it a bit to at least be factual. The statistic about the "weight" was just an eye catcher, put the most interesting info forward, and stuff people can relate to. Changing the sentence about black holes to something like "one outcome of a supernova is a neutron star", or "the supernova of a medium sized star" could be preferrable, and move the other possible outcomes to later in the body. I only started editing this page because it had no image...I hate articles without pictures, humans are visual creatures ;) --Fxer 00:37, July 21, 2005 (UTC)
Part of the current intro is confusing to the lay reader (namely, me):
A typical neutron star has a mass between 1.35 to about 2.1 solar masses, with a corresponding radius between 20 and 10 km (they shrink as their mass increases) — 30,000 to 70,000 times smaller than the Sun.  Thus, neutron stars have densities of 8×1013 to 2×1015 g/cm³, about the density of an atomic nucleus.
Compact stars of less than 1.44 solar masses, the Chandrasekhar limit, are white dwarfs; above three to five solar masses (the Tolman-Oppenheimer-Volkoff limit), gravitational collapse occurs, inevitably producing a black hole.
Now, I'm hardly an astrophysicist, but I'm having trouble understanding exactly how the Chandrasekhar Limit applies to neutron stars specifically.  It doesn't make sense that a neutron star with a mass below the limit would utlimately collapse into a white dwarf.  How exactly does the Limit apply - can someone clarify? UndercoverParrothead 22:48, 14 October 2006 (UTC)
thread_title:  new intro... 

message: Will some knowledgeable person please either add some references establishing the "atmosphere/crust" structural version of a neutron star, or else rewrite it to remove that wording? I'm no astrophysicist, but as a physics grad student and a follower of such things as much as I have been able in the scientific and popular literature, I have never heard of such a thing. Not saying it's false, just that we ought to have some sort of documentation.
:Would a reference to the research on neutron star crusts suffice? Although almost every aspect of neutron stars is theory, we just try to make the theory better and better. The crust appears to make a dramatic difference at low central densities, where the neutron matter is below the neutron drip density, and finite nuclei are still stable. The common reference is
::The Ground State of Matter at High Densities: Equation of State and Stellar Models
::G. Baym, C. Pethick, P. Sutherland
::Astrophysical Journal, vol. 170, p.299
:since this is widely used to calculate the equation of state for the crust. You probably won't find much about crusts in the literature though. Should this go in, or is this too involved?
--JDC 00:32, 4 October 2005 (UTC)
thread_title: Neutron star structure

message: The edit involving the 'fudge factor' is fine by me. The only observational parameters we have (to a decent degree) are mass limits. We construct models to one day test via experiments.
--JDC 23:52, 4 October 2005 (UTC)
thread_title:  Clarification Edit 

message: New stars found called Rotating Radio Transients, or RRATs
http://news.yahoo.com/s/space/20060215/sc_space/astronomersdiscoverpeekaboostars
Can someone create a new article? —The preceding unsigned comment was added by 66.25.142.153 (talk • contribs) .
:It would probably end up being a redirect to this article, with a section added to the neutron star page for rotating radio transients of the type described in the article. If you can provide citations to journal papers or university-hosted web sites about these stars, though, I'm sure it'll get added pretty quickly. Welcome to Wikipedia, and happy editing! --Christopher Thomas 03:09, 16 February 2006 (UTC)
thread_title:  RRAT 

message: I have edited the section that says the Tsar bomb was 100 MT. The bomb (in the form tested) was only 50MT. There was a plan to make a 100MT 'dirty bomb' but this was never tested - nor created I think.
:The difference between those two versions was an uranium tamper which was exchanged shortly before detonation for a lead tamper. So with all respect one can safely say that it is the biggest bomb that was 'built' by mankind, though fortunately not detonated. Knowledge about those bombs was advanced enough at the time to support the untested 100 Mt figure. Endymi0n 18:58, 20 March 2006 (UTC)
thread_title:  Tsar Bomb 

message: "Due to its small size and high density, a neutron star possesses a very high rotation speed..."  Isn't the high rotational speed due to conservation of angular momentum in conjunction with the drastically reduced radius of the star? Clarityfiend 08:39, 9 June 2006 (UTC)
replies: text: Yes, and that's what "small size and high density" refer to, so I'm puzzled by your question. If you think that could be phrased more clearly, go ahead and edit it. --Christopher Thomas 16:25, 9 June 2006 (UTC)
replies: text: One doesn't imply the other. My thanks to Xerxes314 for fixing it (more accurately than I would have). Clarityfiend 02:51, 11 June 2006 (UTC)
thread_title:  Cause of rotational speed 

message: The credit card analogy in the magnetars section is unclear. Does it mean 'wipe' as in demagnetise? Or is 'wipe' a typo for 'swipe', as in it could read the CC info from that distance?--Anchoress 01:10, 24 June 2006 (UTC)
replies: text: It means demagnetize. Numbers for this are suspect, but are still useful for making the strength of the field clear to readers who aren't experts. --Christopher Thomas 06:16, 24 June 2006 (UTC)
thread_title:  Magnetars and AmEx? 

message: To the sentence about what it would be like to fall on a neutron star:
:if an average human were to encounter a neutron star, he or she would impact with roughly the energy yield of a 100 megaton nuclear explosion (a power equivalent to twice the tsar bomba, the biggest nuclear weapon ever detonated)
I had added the comment: and probably not survive.
This contribution of mine to Wikipedia lasted only about 15 minutes; it was reverted by Bryan Derksen, saying:
:a human _probably_ wouldn't survive falling onto a neutron star's surface? Only taxes are as certain. :))
This seems to imply that there is no place for humor on WP, no matter how obvious it might be (my comment certainly could not be taken for serious and mislead someone - let alone lead to serious consequences, like someone really going off to jump on a neutron star, more on that below). Surely someone is going to point to some Be dead serious with a straight face official guideline about that that I overlooked.
However, just for revenge, I want to say that Bryan's own comment is itself misleading; indeed, it is false:
* Taxes are not certain. I hope I won't loose my job, but if I do I won't pay taxes any more. I might also just die (even without the help of a neutron star).
* It is simply not true that a human being would be killed by the impact with a neutron star. That is just simply not true. The human would already be dead before impact. You can't be killed if you are already dead. The human would have been torn apart during descent by the tidal push and pull of the star's gravity.
* The human couldn't get there anyway. The closest neutron star must be light years away, and to get there, even with a modern high-speed train, would take at least tens of thousands of years. Even if you are young and start out today, you very probably will not survive that long. So again, you will not be killed by the impact.
It might be objected that if it is indeed impossible for a human to fall on a neutron star, then any sentence starting by "if an average human were to encounter a neutron star" is true. All implications are true from a false premise. But then it would be just as true to say the impact would produce the energy of a 1000 gigaton bomb, or that of lighting a match. That in turn would mean that the whole sentence is irrelevant, devoid of content. That cannot be the case, see the Everything on Wikipedia is 100% reliable relevant and perfect guideline. So this objection is dismissed.
Now, can I put my comment back?
David Olivier 13:11, 25 June 2006 (UTC)
replies: text: No, I think it's still inappropriate. While humor is not exactly forbidden on Wikipedia, lack of clarity and deliberately misleading statements are. Your statement that a human would "probably not survive" impact on a neutron star suggests that there is some nonzero chance that a human could survive impact on a neutron star. That's simply not true. Your other points above aren't particularly relevant since this is a hypothetical scenario; it doesn't matter how the human got there, it's simply a given that he did. And it doesn't even matter whether he's alive when he hits, the result is the same either way. Bryan 06:32, 26 June 2006 (UTC)

text: I agree that it shouldn't be included. IMO it's not because there's no place for humour in WP, nor is it because of the inaccuracy of the statement. It's because it's irrelevant. The bomb analogy is appropriate because it conveys information about the topic, your addition does not.--Anchoress 04:50, 27 June 2006 (UTC)
thread_title:  The hazards of falling on a neutron star 

message: There's now been 3 instances of vandalism by 172.142.102.49. This is the only page he's editing, but he keeps editing the pulsars section to refer to penises. Took me a second to work it out. Lawful Hippo 04:55, 27 November 2006 (UTC)
replies: text: It means more along the lines of a more massive neutron star has a smaller radius but that aside a neutron star can actually gain mass as can all stars if they exist as part of a binary star system. In the case of a neutron star it has such a massive gravity well that it is common for it to rip mass off of its binary partner and this increases the mass of the neutron star and would decrease it's radius. Allywilson 00:58, 15 March 2007 (UTC)
thread_title:  Vandalism 

message: "The fact that stellar and biological evolution are so slow in our matter universe does not mean that no faster universe is possible. Even today, some people suggest that in the super-fast reactions in the quark soup of neutron stars, living structures with the complexity of civilisations might arise and pass in what to us would be the blink of an eye." 
—Jon Richfield from Sumerset West, South Africa writing a response to a question sent to the Last Word column of the New Scientist, published in Does Anything East Wasps: And 101 Other Quetsions (2005)
I thought this was very interesting. Does anyone know what Jon is talking about? —The preceding unsigned comment was added by 124.62.212.69 (talk) 11:54, 17 February 2007 (UTC)
replies: text: Might be a reference to the possibility of life composed of collapsed matter, as was featured in Robert Forward's novel Dragon's Egg. He proposed that the "nuclear chemistry" such life would be based on would run millions of times faster than the electronic chemistry of known life. Bryan Derksen 20:03, 17 February 2007 (UTC)
thread_title:  Civilisations in the blink of an eye 

message: I saw a news article today on BBC about an irregular neutron star they had discovered named Calvera. I think information about it should be added to the article.Trees r cool 21:59, 20 August 2007 (UTC)
thread_title:  the neutron star that is in the news 

message: Can anyone comment on the validity of the trivia section?  I myself don't know enough about neutron stars to know one way or another.  Thanks. soldierx40k 00:33, 3 September 2007 (UTC)
thread_title: Trivia?