17 Sep 2019 16:08:56 UTC

Topic 219604

(moderation:

This

https://www.rt.com/news/468988-most-massive-neutron-star-detected/

If the data is correct, that's a huge compression.

What do you think, could it be real?

Language

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## John wrote:... What do you

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John wrote:Yes, of course it's real :-). Einstein@Home has detected lots of previously unknown neutron stars over the years. There are likely to be many millions of them in the Milky Way galaxy alone so it's hardly surprising that people keep finding new ones. The only thing 'unusual' is that this one seems to be getting pretty close to the theoretical upper size limit for neutron stars. A bit larger than this is supposedly going to result in a black hole rather than a neutron star. It's good to find these heavier ones as a means of testing that theoretical limit. The theory might not be correct :-).

The article you linked to just seems to be click bait - something to be expected that is presented in a completely sensationalist manner. If you would like to read something rather more factual and less sensational about neutron stars in general, try reading something like this.

Cheers,

Gary.

## John wrote:If the data is

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John wrote:The numbers just boggle the mind, don't they ? :-)

'Neutron star' is a catch-all term for these hyper-dense objects that are one line of stellar evolution after their central nuclear fusion processes reach iron. It's a good thing that there are no close examples for us to study, as they hose their nearby space with all manner of radiations. They inherit the angular momentum and magnetic fields from the original star system and so these are also amazing figures.

As for the mass limit, well,

that depends on what you think the 'equation of state' is for such beasts. That equation would relate the density of it's material ( determining the gravitational field ) to the outward pressure that it generates ( preventing further collapse ). It's probably not going to be that of an ordinary atomic nucleus. What is matter like when you really jam stuff together to that degree ? What force rules within ? Just the forces that we already know of, or something new that only comes into play at such densities ?in theory{ One thing that we do know, by analogy with white dwarves, is a very quantum mechanical characteristic. Neutrons are fermions which roughly means they resist being stacked on top of each other : the Pauli exclusion principle

*& antisymmetric wavefunctions. This gives the more familiar electronic energy level structure and chemical characteristics of everyday matter. Is the Pauli principle always going to apply ? Supposedly this should also prevent a singularity forming within black holes. Cue your favourite guess at 'quantum gravity' .... ;-) }Cheers, Mike.

*The Pauli principle is one of those axiomatic sort of things. It can be related to deeper statements about the universe but it is easier to just accept it as it is.I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal

## Thanks for the tips. Yap,

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Thanks for the tips. Yap, click bait worked on me this time :) That wiki link is really nice.

Mike, lovely questions, food for thought.

## Mike Hewson wrote:..... Cue

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Mike Hewson wrote:I've just finished a book by Carlo Rovelli called

, tremendously well written and for a general audience. He speaks of theReality Is Not What It Seems( LQG ) attempts that have been made in recent years. It's not a competitor to String Theory, which aims at force unification, but a direct throw at literally quantizing spacetime. LQG tries to meld Quantum Field Theory with General Relativity, andLoop Quantum Gravityaccidentally unify as a side effect.mayThe logic is roughly as follows : the primary foundation of reality is fields of all sorts, fields are assumed as basic elements without other justification, thus the gravitational field is one of them, hence to quantize this field is to quantize space & time. This places a lower limit on the size of a volume of space and a tick of time. The scale at which this exists is incredibly small, you start with the Planck length ~ 10

^{-thirtysomething }metres^{*}, that being the size of the event horizon for a particle becoming a teensy weensy black hole. In other words one can't probe ( read : measure ) any smaller distance because particles can't come any closer without disappearing. Thus the minimal spatial volume becomes ~ 10^{-hundredish }metres^{3}. LQG claims thatbelow that scale. All fields lie one upon another as it were. An excitation of spacetime becomes the graviton, similar to an excitation ( read : resonance ) of the electromagnetic field being a photon.nothing existsThe

bit comes in by tracing paths that go around spacetime in, well, a loop ( the starting point is the end point of some traversal ). In the theory the minimal volumes are modelled as nodes which are connected via adjacent common areas. One could visualise this as all manner of polyhedra squeezed together cheek by jowl. Spin enters the discussion here for reasons I didn't quite catch, but anyway it is possible to parallel transport a spin vector around a loop and hence deduce any curvature of spacetime if said vector doesn't point in the same direction as when it started. This curvature is the very same that Einstein's General Relativity speaks of. Hence we have satisfied Quantum Mechanics and GR. GR is the higher scale approximation to LQG. Plus with a minimum volume restriction you sneak out of the singularity/infinity problems of classical GR : numbers can be horrendously large but still finite. Maximum density for a black hole anyone ? :-0loopThe really anti-intuitive bit is ( of course there's a price to pay ) that to be truly-rooly consistent with QM then one must accept that probability comes into the description of spacetime structure. Down at the Planck length all possible structures act like superposed QM states with complex amplitudes, and thus need to be integrated

^{**}( by Feynman's sum over histories or lattice approximations ) to yield the most probable actual structure if measured ( read : probed ).But it is a work in progress and much remains to be figured out. The good news is that if successful they expect to be able to produce testable numbers ie. confront the theory with observation. Unlike String Theory which has left the tent flap open and has gone AWOL in a blizzard of mathematics.

Cheers, Mike.

* The Planck time is 10

^{-fortysomething}of a second : the time taken for light to travel the Planck length. I put that in to be complete, but that's a hard ask to conceptualise such a short interval. I have enough trouble with the 10^{-twentysomething}that LIGO measures.** This introduces the issue of boundary conditions, what 'really' happened within some time interval and like quantum conundrums. It's hard to accept I think that a definite ordering of events is a luxury of our human scale. Specifically down at the spacetime foam, as it is called, cause and effect are somewhat blurred. One is left with the idea that some of the contributing states are specifying that things may occur out of causal order, but as long as the state meets given boundary conditions then it may contribute to a summation. In fact it is actually hard to put this aspect into normal language, which is a product of our scale of reference.

At a classical scale this is reminiscent of out of order execution of computer code : take two tasks that can be done in either order, but in the program code one will be written as sequentially before the other. Now imagine that one task knows the result of the other before it is done. It's something like that. Weird.

I have made this letter longer than usual because I lack the time to make it shorter. Blaise Pascal