[HN Gopher] Neutron stars may be bigger than expected, measureme...
___________________________________________________________________
Neutron stars may be bigger than expected, measurement of lead
nucleus suggests
Author : furcyd
Score : 110 points
Date : 2021-04-27 15:35 UTC (7 hours ago)
(HTM) web link (www.sciencemag.org)
(TXT) w3m dump (www.sciencemag.org)
| jvanderbot wrote:
| Obligatory: Bigger in size, but not mass, meaning less dense
| overall, based on results showing the thickness of the atomic
| nuclei of lead isotopes. (which includes the radius of the thick
| shell of neutrons around the nucleus, which was wider than
| expected).
| cletus wrote:
| Let me add some perspective here. This only became apparent to me
| fairly recently and it blows my mind. It's something I hadn't
| thought of before.
|
| Black holes are relatively "simple". I mean that you can
| completely define a black hole with 3 properties, one of which
| isn't really relevant.
|
| The two most relevant properties are spin and mass. The last is
| electric charge. The reason this is somewhat irrelevant is
| because electric repulsion is about 60 orders of magnitude more
| than gravitational attraction so it's not expected black holes
| have a significant charge.
|
| Neutron stars OTOH are arguably the most complex objects in the
| Universe. Why? Because you're dealing with gravity, electric
| charges, nuclear forces and QCD such that there's no equation of
| state for describing dense nuclear matter.
|
| Probably my favourite variant of neutron stars is the extremely
| rare magnetar [1], the most powerful we've found has a magnetic
| field 100 trillion times that of Earth's [2]. This field is so
| strong it would flatten atoms and rip electrons from your body.
|
| So as much difficulty as we have of describing the nucleus of an
| atom (as referenced in this post), imagine a whole star of that
| stuff.
|
| [1]:
| https://en.wikipedia.org/wiki/Magnetar#:~:text=A%20magnetar%....
|
| [2]: https://www.space.com/magnetar-eruptions-sculptor-
| galaxy#:~:....
| ohazi wrote:
| Neutron stars seem like what you _would_ see in a black hole if
| the interesting parts weren 't shrouded by an event horizon.
| Although I suppose the event horizon does give you jets.
|
| But yeah, city-sized objects with the density of an atomic
| nucleus. Pretty mind-bending! (literally, I guess?)
| CuriouslyC wrote:
| Imagine if black holes were just neutron stars made of second
| or third generation quark "neutrons."
| ramraj07 wrote:
| The "how to build a black hole" video from PBS space time
| says that's how you do it - you start with a neutron star and
| keep adding more mass to it, which paradoxically makes it
| smaller until it becomes smaller than its swarzchild radius,
| becoming a black hole. Blew my mind and anyone else's when I
| share the video with them!
|
| https://youtu.be/xx4562gesw0
| cletus wrote:
| That depends on what size of black hole you want to make.
| It works for large black holes (you need sufficient mass
| for the gravitational forces to be sufficient) but those
| black holes aren't that useful.
|
| Smaller black holes are harder to construct but way more
| useful.
| willis936 wrote:
| It's simple, just deflate spacetime!
| elseweather wrote:
| I'm curious what useful applications we have for black
| holes of any size
| jakeogh wrote:
| It's assumed that little ones are the most efficient mass
| to energy converters, via Hawking radiation.
| cletus wrote:
| There are actually a lot of theoretical applications.
|
| Black holes are likely the most efficient form of power
| generation that we currently know of.
|
| Black hole propulsion may well be the best form of
| interstellar starship propulsion.
|
| Black holes may also be the ultimate computer.
|
| If the universe continues based on it current
| understanding then eventually all the stars will be dead
| and the universe will be a dark place. The Black hole era
| will last trillions of time as long but may well be the
| golden age of civilization.
|
| Each of these topics is a rabbit hole.
| firebaze wrote:
| Really don't want to be dismissive, but this guy appears to
| me as having one gesture (both hands towards the viewer, to
| underscore the graveness of his words), a good haircut and
| that's about it.
|
| If find it hard to take a presentation like this serious.
| Most of the mentioned facts are right as far as i can judge
| it without having a major in physics, but to me this is so
| very much worse than a link to backreaction (Sabine
| Hossenfelder), startswithabang (Ethan Siegel) or almost any
| other serious physics blog out there as anything else.
|
| I suppose this will get downvoted, and I'm fine with that,
| but please explain to me why a self-promoting video guy
| with probably 5% understanding of the matter compared to a
| serious pop-sci blog is so relevant to you.
|
| Heck, even wikipedia has more information than this clip.
| And it doesn't cost 13 minutes + ads, just 5 minutes to
| read.
|
| It's not a paradox a neutron star gets smaller the more
| mass you add to it. This is also true for Jupiter-sized
| objects; it is a function of density, matter and gravity,
| and not related (in this case) to special relativity.
| LASR wrote:
| Lots of assumptions in your comment. They happen to be
| very wrong.
|
| Maybe as a default position, you should assume less about
| someone's credentials based on hand gestures and
| haircuts.
| nynx wrote:
| Matt O'Dowd is a well-known physicist. I'm not sure why
| you feel that you can judge him so quickly.
| ramraj07 wrote:
| I have no idea what you're talking about? It's a pbs
| YouTube channel, the host is a professor in astrophysics
| and has generally made sure he doesn't oversimplify
| anything. I like Sabine's videos sometimes when she's not
| bonkers kookoo but this guys not trying to be
| controversial.
| gizmo686 wrote:
| That self-promoting video guy is an astrophysicist, with
| a significant amount of papers published about black
| holes.
|
| You are free to not like his mass-market material, but
| from a technical level, he is quite qualified to talk
| about the subject.
|
| https://en.wikipedia.org/wiki/Matt_O%27Dowd_(astrophysici
| st)
|
| https://www.mattodowd.space/
|
| https://ui.adsabs.harvard.edu/search/p_=0&q=author%3A%22O
| 'Do...
| hinkley wrote:
| I've seen a couple astrophysics videos over the last few
| years that put forward the theory that many black holes are
| the result of a neutron star forming in a binary or trinary
| star system. The initial explosion and the ejecta creating
| a situation where the neutron star begins to siphon
| material off of its partner.
| ravi-delia wrote:
| I was under the possibly incorrect impression that black
| holes result when the gravitational force is so great that it
| even overcomes Pauli's exclusion principle, collapsing the
| neutrons into an overlapping mass of staggering density. Now
| that I write that out, I'm a little more doubtful.
| jfengel wrote:
| Not exactly.
|
| A black hole doesn't have to be very dense. The larger it
| is, the less dense it needs to be to prevent light from
| escaping. The supermassive black hole at the center of our
| galaxy may be less dense than water[1].
|
| For black holes closer to a single solar mass, then yes,
| they will be super dense, and the degeneracy pressure helps
| keep it from becoming a black hole. You have to add enough
| mass to overcome the degeneracy pressure for it to develop
| the event horizon that makes it a black hole.
|
| But not all black holes do that. Others can simply keep
| acquiring mass without that violent sudden event. They just
| gradually cross the point where no light can escape, but
| you might not even notice looking at it. The light just
| keeps gradually shifting redder and redder until the
| wavelength becomes infinite.
|
| [1] https://en.wikipedia.org/wiki/Sagittarius_A*
| hinkley wrote:
| Last update I heard on black holes was that the space
| inside of them increases at the speed of light. That's a
| hell of a lot of space inside of an event horizon.
|
| I'm still fond of the theory that our universe is in fact
| inside of a black hole, and that the big bang is 'just'
| the moment we went supercritical.
|
| One thing I don't understand about naked singularities -
| if you were inside of one, the lack of an accretion disk
| would allow you to see out of it, right? Could you detect
| that you are looking out across an event horizon?
| btilly wrote:
| Close.
|
| Giant blue stars burn all of the way up to the most stable
| element of all, which is iron. And then collects an iron
| core. As the core grows, the star shrinks and the pressure
| in the middle grows. Once the pressure in the middle is
| high enough, it overcomes the Pauli exclusion principle and
| electrons merge with protons to become neutrons with a
| release of energy, which mostly comes out as neutrinos.
|
| Once a bit of that core disappears, the stuff around falls
| into the new gap, hits it, goes under way more pressure and
| the same thing happens. This starts a chain reaction that
| causes a supernova. The core collapses into a neutron star
| while the release of energy blows the outer shell out to
| eventually become a nebulae.
|
| If the initial star was big enough, the newly created
| neutron star is big enough to transform into a black hole.
| Otherwise it is left as a neutron star.
|
| If it forms a neutron star, the spin speeds up thanks to
| the collapse. Typical time to rotate can be anywhere from
| milliseconds to seconds. We can tell that because its
| magnetic field also gets trapped and forms a strong beam
| along the north and south magnetic poles. Since magnetic
| poles do not generally line up with the rotational poles,
| that beam becomes like a searchlight. If we're in the path
| of that beam, we see a pulsar, and the frequency of the
| pulsar is the rotational speed of the neutron star.
|
| This is probably way more than you wanted to know. :-)
|
| I probably also am going to get corrected on some details
| in 3, 2, 1...
| robocat wrote:
| Your comment did inspire me to go looking for the
| distribution of elements within the iron core: "carbon,
| neon, oxygen, and silicon burning leave a core composed
| of iron, cobalt, nickel, and neighboring species,
| referred to as the iron-peak nuclei".
|
| For anyone else interested in a readable article on a
| slightly more detailed look at supernova than wikipedia,
| and a discussion on the difficulties of modelling
| supernova, I liked this article:
| https://aip.scitation.org/doi/10.1063/1.4870009
| hinkley wrote:
| I was shocked to learn how long it takes a photon
| produced at the center of the sun by a fusion event to
| reach earth. The layers upon layers of subatomic
| particles that are all interacting in these tight
| quarters is simply astounding.
|
| I've heard this same theory on supernovas from a number
| of people in or around physics, but I always wonder how
| handwavy it is, whether we _actually_ understand how that
| works yet, and how different (confusing) the real process
| is from the given one.
| chasd00 wrote:
| seems like i was under the _likely_ incorrect impression
| black holes have mass but no volume (singularity and all..)
| and so infinite density. But, then again, what happens
| beyond the event horizon is meaningless anyway.
| throwawayboise wrote:
| The description I have heard is that a black hole
| contains no matter at all, it is all energy expressed as
| infinitely(?) warped space and time.
| hinkley wrote:
| I remember the infinities of black holes being a challenge to
| explain to my artsy friends after reading _A Brief History of
| Time_.
|
| Correct me if I'm wrong, but isn't the curvature of space
| around - and within - a neutron star substantial enough that
| euclidean geometry doesn't really hold anymore? The volume of
| a basketball is the surface area x R/3, but is that true of a
| neutron star? I was under the impression that the difference
| between Euclid and actual was statistically significant, to
| the point that you get the wrong behavior if you don't
| account for it.
| Groxx wrote:
| > _In 2020, a fast radio burst (FRB) was detected from a
| magnetar.[7][8][9][10][11][12][xss ns]_
|
| Wikipedian humor at its finest. Because _of course_ "excessive
| citations" looks like a citation.
| yongjik wrote:
| > This field is so strong it would flatten atoms and rip
| electrons from your body.
|
| ...which is underselling it a bit. :)
|
| (As quoted in Wikipedia) the field is so strong that pure
| vacuum itself has ~10,000 times the density of lead, due to the
| energy contained in the field. Imagine that.
| jayd16 wrote:
| >The reason this is somewhat irrelevant is because electric
| repulsion is about 60 orders of magnitude more than
| gravitational attraction so it's not expected black holes have
| a significant charge.
|
| I hadn't thought about it but I guess that means protons or
| electrons have a maximum resting density. A group of those will
| never collapse from gravity?
| Tagbert wrote:
| If that were true, you would not get a neutron star where the
| electrons and protons are collapsed into neutrons. Not sure
| how that stands to the overall strength question, though.
| throwaway2568 wrote:
| Protons and electrons are both Fermions, which means they can
| not have identical quantum numbers (have to obey the Pauli
| exclusion principle as mentioned elsewhere in the thread). In
| the case of a very dense system, like the sun, this can lead
| to an effect known as degeneracy pressure (which acts against
| gravity). Essentially you have filled all the lower quantum
| numbers and then adding an extra proton/electron to the
| system requires a certain amount of energy. It's quite
| handwavy but the degeneracy pressure of electrons is mostly
| what keeps a white dwarf from contracting, whereas in the
| case of a neutron star it is the degeneracy pressure of
| neutrons (plus repulsive strong force and other effects as
| indicated in the OP). This kind of high level discussion is
| often covered in first year astronomy courses auditing a MOOC
| like the following may be of interest
| (https://www.edx.org/course/astrophysics-the-violent-
| universe)
| detritus wrote:
| > Neutron stars OTOH are arguably the most complex objects in
| the Universe.
|
| In OUR universe, at least.
|
| If a black hole ends in a white hole, Gosh only knows how
| complex things will end up at the other end. Witness, for
| example, our entire reality.
| btilly wrote:
| _Black holes are relatively "simple". I mean that you can
| completely define a black hole with 3 properties, one of which
| isn't really relevant._
|
| Classically, yes. But more recently we've discovered not.
|
| One of the major conundrums about black holes is how
| information gets lost in their creation. There is a lot more
| information in the stuff that creates a black hole than in the
| black hole itself. Which violates the third law of
| thermodynamics. This is called the Black Hole Information
| Paradox.
|
| But as https://blogs.scientificamerican.com/observations/have-
| we-so... explains, the real state of a black hole includes all
| of the stuff that you can see in the process of falling in. (We
| never actually see anything hit the event horizon. And in
| theory something on its way there can still be retrieved a
| million years after it started falling.) When you track things
| carefully, a real black hole is a very complex thing indeed.
| With no information loss.
| colechristensen wrote:
| This brings up a question I have had for a while: what is the
| life story of a photon shot at a black hole?
|
| From an outside observer, presumably you shoot a laser at a
| black hole and if your photons don't hit anything on the way
| to the horizon, they never hit it either but just approach
| asymptotically as time goes to infinity.
|
| As, a photon though, you don't "notice" crossing the horizon
| and in a measurable amount of time you go from being emitted
| to hitting the singularity.
|
| Black holes don't last until infinity though, they evaporate
| in a large but measurable time. (let's say 10^100 years, it
| depends on time and how the universe dies and how big the
| black hole is, but whatever, presuming it happens it is some
| extraordinarily large number of years)
|
| So... as something falling into a black hole an outside
| observer will watch you infinitely slowly approaching a
| growing horizon until at some point the growth goes negative
| and you watch the horizon falling away from your friend the
| photon until at last the horizon disappears entirely and
| releases the photon to go about its merry way to hit
| something sometime around the heat death of the universe.
|
| In other words, if you are a conscious very resilient little
| particle doomed to fall into a black hole... do you really
| appear from the outside to be falling in until the black hole
| evaporates? Do you experience going through the event horizon
| like it's nothing and hit the singularity in a few hours by
| your own watch...
|
| Or is a black hole sort of a time machine to the end of the
| universe where in the short process of falling in you get to
| watch the whole history of existence pass you by and you come
| out at the end having never crossed the horizon in what was
| for you a very short ride.
|
| Or is there some third option where from the outside it takes
| an infinite amount of time for you to fall in, but that
| infinity "for math reasons" actually takes place and passes
| in a Zeno's paradox kind of way at some distinct point in
| your timeline and you meanwhile pass the horizon and hit the
| singularity in short order and are no more?
|
| I don't really know anything but these are questions and
| vague thoughts I have had. The central question is
| reconciling the outside apparent infinite time to watch
| something cross an event horizon with the finite lifespan of
| evaporating black holes.
| bpodgursky wrote:
| Well, the other wrinkle here is that the "singularity" is a
| mathematical approximation. There's no such thing as
| hitting it -- from the outside, you just move
| asymptotically slower as you approach it.
| btilly wrote:
| Not so fast. Black holes have a singularity in the
| middle, and an event horizon around them. There is no
| singularity at the event horizon, and that is all that we
| can see..
| juloo wrote:
| There might be naked singularities in case of a rapidly
| rotating black hole. The singularity would have a donut
| shape and might be outside of the event horizon.
| https://en.wikipedia.org/wiki/Naked_singularity
|
| Of course, this is very theoretical and we don't actually
| expect that to exist.
| btilly wrote:
| Huh, I thought that naked singularities were thought to
| not exist. But apparently in 2018 someone found a case
| where they could.
|
| Thanks!
| juloo wrote:
| You move asymptotically slower from the point of view of
| the particle falling in the black hole. From outside the
| black hole, the falling particle should fall into the
| black hole at a speed close to the speed of light. (but
| we can't observe that from the outside)
|
| The image an outsider would see "printed" on the black
| hole has nothing to do with where the falling particle
| is.
| btilly wrote:
| That's officially above my pay grade. :-)
|
| Seriously my course in general relativity was about 30
| years ago. And work on the information paradox work is
| about exactly what you're talking about.
|
| I honestly don't fully know what happens when you're
| approaching a growing black hole. Do you cross the horizon
| then?
| juloo wrote:
| As a particle, you continuously accelerate even after the
| event horizon (which you don't realize). Immediately after
| you passed the horizon, any photon you can send won't ever
| leave the black hole.
|
| What outside observers will see "frozen" is the instant
| just before you cross the horizon. A bit like if your image
| 1ms before you cross the horizon will be seen by the
| observers years after, your image 1us before will be seen
| millions of years after, etc...
| colechristensen wrote:
| But... let's watch that image or at least keep a model of
| our friends falling into the black hole for 10^100 years.
| Forever is a long time.
|
| If we keep watching that image the black hole eventually
| stops growing, the "image" never crosses the event
| horizon and when the universe cools down enough the event
| horizon starts getting smaller and hotter until we watch
| our friends getting roasted outside the evaporating black
| hole which eventually is gone and just normal matter.
|
| The timeline of the "image" would seem to reconnect with
| the real article having never crossed the event horizon.
|
| In other words it would seem if we waited long enough the
| image of our friends outside the event horizon would
| outlive the black hole and we could go say hello after it
| evaporated.
|
| In other, other words, how do we see the universe outside
| aging as we fall into a black hole? Do we not get to
| watch the heat death of the universe as we approach and
| consequently the black hole very quickly evaporating in
| front of us as we fall towards it?
| cletus wrote:
| Wasn't the issue of black hole information loss the subject
| of the Hawking-Thorne bet that Hawking eventually conceded
| (that black holes didn't destroy information)? [1]
|
| (This may be a separate issue; I'm genuinely curious).
|
| [1]: https://physicsworld.com/a/hawking-loses-black-hole-
| bet/#:~:....
| gus_massa wrote:
| All the stuff around a black hole and in a black hole is
| under a lot of tidal forces and will be crushed and crumbled.
|
| Imagine a blender. According to quantum mechanics, using a
| blender for an hour is an unitary transformation, so it will
| not destroy the information, and it's an invertible
| operation, you can reconstruct the original items. [And even
| a classic blender is invertible at the molecular level. It's
| only not invertible if you consider the friction and other
| average macroscopically properties.] Anyway, after an hour of
| blending, you will get a horrible homogeneous mix.
|
| But (if the current models are correct) a Neutron star is
| very different in the crust that is a few km near the
| surface. It has many levels with different properties that
| are called "nuclear pasta"
| https://en.wikipedia.org/wiki/Nuclear_pasta and one with
| graphics that explain the names
| https://astrobites.org/2017/10/05/nuclear-pasta-in-
| neutron-s...
|
| Going again to the blender example, it's like a bad blended
| mix, that has foam at the surface, a liquid in the middle and
| solids at the bottom.
| btilly wrote:
| It depends on the size of the black hole. One with the mass
| of the Sun would rip your head from our feet under a tidal
| force of thousands of gravities. One the size of the
| monster at the heart of our galaxy has tidal forces so
| gentle that you wouldn't even notice them until after you
| were inside the event horizon.
|
| If this seems non-intuitive, remember that the
| Schwarzschild radius varies linearly with mass, and tidal
| forces scale like mass / radius^3. So tidal forces at the
| event horizon scale like 1/mass^2. A black hole that is 100
| million times heavier will have tidal forces that are 10
| quadrillion times smaller at its event horizon.
| jihadjihad wrote:
| > Which violates the third law of thermodynamics
|
| Wouldn't this be a violation of the second law rather than
| the third?
| willis936 wrote:
| It's not quite Maxwell's demon because the event horizon is
| a one-way causal ticket. The information might not be
| destroyed but it is totally inaccessible on this side of
| the horizon.
| btilly wrote:
| I just looked it up, and it is a violation of the fact that
| the laws of physics should be reversible. So from the wave
| function at any point of time you should be able to
| reconstruct the wave at any other.
|
| My bad for having stuck thermodynamics in there at all. :-(
| carabiner wrote:
| A spoonful weighs a ton.
| ThePhysicist wrote:
| As a physicist I still find it fascinating that you can study
| some of the smallest things in the universe and learn something
| about some of the largest things in it.
| srl wrote:
| Relatedly, NICER (an X-Ray telescope) launched in 2017, and has
| been observing pulsars to get radius measurements since then. See
| for instance https://arxiv.org/abs/1912.05705. (I think there's a
| more recent measurement but I can't find it on arXiv.)
|
| I don't have a good understanding of the relationships between
| all the different methods, but I do know that NICER's
| measurements have systematically given larger radii (albeit with
| huge error bars) than other methods do.
| dsp_person wrote:
| Really enjoyed Dragon's Egg about life on a neutron star.
|
| > The adults of the star's most intelligent species, called
| cheela (no flexion for gender or number), have about the same
| mass as an adult human. However, the extreme gravity of Dragon's
| Egg compresses the cheela to the volume of a sesame seed,[2] but
| with a flattened shape about 0.5 millimeters (0.020 inches) high
| and about 5 millimeters (0.20 inches) in diameter. Their eyes are
| 0.1 millimeters (0.0039 inches) wide. Such minute eyes can see
| clearly only in ultraviolet and, in good light, the longest
| wavelengths of the X-ray band
|
| > By humans' standards, a "day" on Dragon's Egg is about 0.2
| seconds
|
| https://en.wikipedia.org/wiki/Dragon%27s_Egg
| klank wrote:
| In a similar vein, I recommend Stephen Baxter's "Flux". It
| takes place in a civilization that evolved inside of a neutron
| star.
|
| https://en.wikipedia.org/wiki/Flux_(novel)
| farrelle25 wrote:
| Yes I thought "Dragons Egg" was a classic. I remember reading
| it as a child and getting interested in Physics.
|
| I read it's an example of the "hard" science fiction genre - I
| think the author Robert Forward was actually a physicist...
| gizmo686 wrote:
| Since I happen to have _Dragons Egg_ on my desk, from the
| "About the Author" section:
|
| > Dr. Robert L. Forward is a senior scientist at the Hughes
| Research Labs in Malibu, California. Dr. Forward is one of
| the pioneers in the field of gravitational astronomy,
| participating at Maryland University in the construction of
| te first antenna for detection of gravitational radiation
| from supernovas, black holes and neutron stars. (The antenna
| now resides in the Smithsonian Museumm.) At Hughes, Dr.
| Forward constructed the first laser gravity antenna and
| invented the rotating gravitational mass sensor. ...
|
| Fun fact, the start of Dragons Egg (copyright 1980) is April
| 2020
| Causality1 wrote:
| A classic indeed. I seem to recall that jumping off a high
| cliff or from a hovering vehicle was deadly to them because
| without the crushing gravity their bodies exploded into a cloud
| of "regular" matter.
| gizmo686 wrote:
| They even have an entire field dedicated to "expanded matter
| physics".
| excalibur wrote:
| We're talking about stars here. The difference between 10 km and
| 14 km is pretty negligible at this scale, these are both specks.
| ben_w wrote:
| If they neutron stars are bigger at any given mass, that
| implies black holes have different minimum sizes, which has
| implications for other things in cosmology.
| at_a_remove wrote:
| Ah, no. Neutron stars have some kind of average density.
| That's ... not applicable to black holes in any real sense.
| Their sizes would not change and are pre-determined by a
| relatively simple formula in the case of non-rotating black
| holes without any significant charge.
| ben_w wrote:
| I'm not suggesting otherwise.
|
| I'm saying that "neutron stars have lower density than
| previously thought" means "neutron stars can be more
| massive before reaching constraint of Schwarzschild radius
| for given mass".
| treeman79 wrote:
| Well they gave a real density size and shape, it just
| doesn't matter.
|
| Inside could be shaped like a dolphin a potted plant or a
| whale. Outside of horizon we couldn't tell from outside.
| DougMerritt wrote:
| As cletus said above, black holes have only three externally-
| observable properties: mass, angular momentum, and charge;
| see for instance [1].
|
| Note that radius/size is not one of those three. The radius
| of a black hole derives from its mass under general
| relativity, and no amount of change found in the density nor
| size of neutron stars will change that.
|
| You're right that new understanding of neutron stars has
| implications for other things in cosmology, though.
|
| [1] https://phys.org/news/2020-12-black-holes-gain-powers-
| fast.h...
| adgjlsfhk1 wrote:
| What this changes is how much mass a neutron star can have
| before it collapses into a black hole. That limit is
| defined by when the neutron star's mass fits within the
| size of an equally massive black hole.
| DougMerritt wrote:
| Not exactly. Certainly it is a black hole once a neutron
| star's mass fits within a certain radius, but since it is
| then not a neutron star any longer, the question is how
| that condition came about.
|
| Neutron stars have an effective outward pressure that is
| caused by the Pauli exclusion principle [1]; two or more
| fermions such as neutrons cannot be in the same state
| (which includes location). A strong enough inward counter
| force from internal gravity (or from an external force)
| will cause a net motion inward, overcoming the outward
| force, such that enough matter (more accurately, enough
| mass-energy, not just matter) is within the critical
| region.
|
| See for instance [2]
|
| [1]
| https://en.wikipedia.org/wiki/Pauli_exclusion_principle
|
| [2] https://www.forbes.com/sites/startswithabang/2018/06/
| 13/the-...
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