[HN Gopher] A bug's life: Millimeter-tall mountains on neutron s...
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A bug's life: Millimeter-tall mountains on neutron stars
Author : dnetesn
Score : 49 points
Date : 2021-07-19 09:59 UTC (1 days ago)
(HTM) web link (phys.org)
(TXT) w3m dump (phys.org)
| swayvil wrote:
| MISSION OF GRAVITY by Hal Clement.
|
| Addresses this very scenario.
|
| A fine fine bit of scifi.
| bookofjoe wrote:
| A wonderful, wonderful book. Captain Barlennan is a fantastic
| character. Time to reread this magnificent story.
| keithwhor wrote:
| > Neutron stars are some of the densest objects in the Universe:
| they weigh about as much as the Sun, yet measure only around 10km
| across, similar in size to a large city.
|
| I'm going to be the Hacker News pedant here and say that this
| sentence bugged me. Weight is a measurement of force. Mass is the
| word they were looking for.
| TheDudeMan wrote:
| Just wait until you see the next sentence.
| jeffwass wrote:
| One "wow" moment that blew me away during my grad physics studies
| was the realisation that a neutron star is effectively one
| gigantic atomic nucleus.
| Florin_Andrei wrote:
| That's stretching quite a bit the definition of a nucleus.
|
| Neutron stars are held together by gravity, not nuclear forces.
| Also, the mix of particles is very different from an actual
| nucleus. The physics are pretty different.
|
| It's a bit like saying the SpaceX Starship, and my mechanical
| pencil are the same thing, because they have the overall same
| shape, and are made of stainless steel.
| jeffwass wrote:
| > Neutron stars are held together by gravity, not nuclear
| forces.
|
| Neutron stars are governed by both gravitational and the
| strong force. [edited]
|
| Quite different from ealier phases of stars which are held
| together by gravity.
|
| > Also, the mix of particles is very different from an actual
| nucleus.
|
| Which particles? The key difference vs an atomic nucleus
| other than the immense size is that the neutron star is not
| charged like an atomic nucleus, as most of the precursor
| star's protons and electrons have fused into neutrons.
| Florin_Andrei wrote:
| https://en.wikipedia.org/wiki/Neutron_star#Density_and_pres
| s...
|
| > _In popular scientific writing, neutron stars are
| therefore sometimes described as "giant nuclei". However,
| in other respects, neutron stars and atomic nuclei are
| quite different. A nucleus is held together by the strong
| interaction, whereas a neutron star is held together by
| gravity. The density of a nucleus is uniform, while neutron
| stars are predicted to consist of multiple layers with
| varying compositions and densities._
|
| It's just a pop-sci meme.
|
| As for the structure, see here:
|
| https://en.wikipedia.org/wiki/Neutron_star#Structure
| jeffwass wrote:
| I have a feeling you're just trolling for trolling sake.
|
| I'll only comment on one part of the Wikipedia quote
| regarding constant densities of atomic nuclei.
|
| The neutron star will have a constant density on any
| length scale as large as an atomic nucleus. The layered
| structure manifests over length scales of kilometers,
| which is 10^18 times larger than an atomic nucleus.
| Florin_Andrei wrote:
| It could also be that your understanding of neutron stars
| may be superficial - you may feel, however strongly, that
| you understand this topic, while reality may be
| different. Have you considered that hypothesis?
|
| Nobody who actually works in fields related to nuclear
| physics or astrophysics considers a neutron star as being
| "just a giant nucleus", no matter how often that image
| may be used in pop-sci articles and youtube videos.
|
| More linky stuff, again related to your statement that
| neutron stars are held together by the nuclear force
| (which is false):
|
| https://www.nuclear-power.com/nuclear-power/reactor-
| physics/...
|
| > _Since they have some similar properties as atomic
| nuclei, neutron stars are sometimes described as giant
| nuclei. But be careful, neutron stars and atomic nuclei
| are held together by different forces. A nucleus is held
| together by the strong force, while a neutron star is
| held together by gravitational force._
| jeffwass wrote:
| > Nobody who actually works in fields related to nuclear
| physics or astrophysics considers a neutron star as being
| "just a giant nucleus".
|
| Sigh. Do you actually work in the field?
|
| Frankly I'm not sure why you felt the need to shit all
| over my "wow" moment originally mentioned. But thank you
| very much for your pedantic comments that could have been
| presented in a constructive non-trolling way.
|
| Since you like links, and since you say nobody in the
| field would ever make this comparison, here are some
| actual professionals saying the same thing in similar
| fora to hacker news. Will you go troll them too?
|
| From the folks at the Chandra X-ray telescope :
|
| https://chandra.harvard.edu/xray_sources/pdf/neutron_star
| s.p...
|
| "Such extreme forces occur in nature when the central
| part of a massive star collapses to form a neutron star.
| The atoms are crushed completely, and the electrons are
| jammed inside the protons to form a star composed almost
| entirely of neutrons. The result is a tiny star that is
| like a gigantic nucleus and has no empty space."
|
| From Prof. Mark Alford, chair of physics at Washington
| University of St Louis
|
| https://www.symmetrymagazine.org/article/five-extreme-
| facts-...
|
| "A neutron star is basically a giant nucleus, says Mark
| Alford, a professor at Washington University."
|
| From a transcript of a lecture by Prof. Ian Morison, 35th
| Gresham Professor of Astronomy :
|
| https://www.gresham.ac.uk/lecture/transcript/print/ageing
| -st...
|
| "When stars, whose total mass is greater than ~ 8 solar
| masses, but less than ~ 12 solar masses, collapse the
| result is a Neutron Star - the core being supported by
| neutron degeneracy pressure as described above. The
| typical mass of such a neutron star would be ~ 1.4 solar
| masses so that it is, in effect, a giant nucleus
| containing ~ 10^57 neutrons."
| BitwiseFool wrote:
| Fascinating, do you know if protons can exist within neutron
| stars? That would make it each one an element, right? Or if
| not, they would all be isotopes of Neutronium?
| dredmorbius wrote:
| There's a gradient of material.
|
| At the core, a neutron star is likely very nearly pure
| neutronium, as other particles simply won't exist long under
| the conditions present.
|
| As depth decreases, other particles can exist, and at the
| surface there are likely free nuclei and atoms of elements,
| though my probably with low nuclear potential. Fission and
| fusion would be accelerated by the energies involved.
|
| That's a lay reading / bits of stray collected memories,
| though quick checking seems to confirm most of this. See:
|
| https://heasarc.gsfc.nasa.gov/docs/objects/binaries/neutron_.
| ..
| [deleted]
| Florin_Andrei wrote:
| There are no isotopes with neutron stars because they are not
| actually nuclei.
| Thorondor wrote:
| Yes, it's thought that neutron stars are about 5-10% composed
| of protons and electrons. In fact, that's why a neutron star
| can have a magnetic field - charged particles are required to
| carry an electric current.
| ziotom78 wrote:
| However, in principle there should be a (perhaps very
| small?) component due to the inner magnetic momentum of
| neutrons [1], right? After all, they are made of quarks,
| which have nonzero charge.
|
| [1] https://en.wikipedia.org/wiki/Neutron_magnetic_moment
| willyg123 wrote:
| This is an enjoyable and worthwhile lecture by Jocelyn Bell, who
| discovered pulsars:
|
| https://www.youtube.com/watch?v=-335gUOvdhA
| mongol wrote:
| Just watched it, very worthwhile!
| thunderbong wrote:
| Amazing. Thank you!
| dark_star wrote:
| A good science fiction book about an intelligent alien race that
| evolved on the surface of a neutron star, written by a physicist:
|
| https://www.goodreads.com/book/show/263466.Dragon_s_Egg
| Beldin wrote:
| I came across a synopsis of this book a week or so ago, read
| about the time differential and it got me wondering: what's the
| explanation for the time differential?
|
| We know that time passes slower in stronger gravitational
| fields. A neutron star has an enormously strong gravitational
| field near its surface, so time should move much slower there,
| not much faster... but in the book it's the other way around.
| (According to the synopsis.)
|
| Am I missing something?
| cfallin wrote:
| The explanation in the book is that neutron-star life is
| based on nuclear chemistry, whose reactions move much more
| quickly than our (electron-shell-based) chemistry, so
| everything happens much more quickly as a result.
| op00to wrote:
| Came here to post this. Love re re re reading this book.
| aatharuv wrote:
| That was just for sale a few days back on the Kindle store (at
| least in the US). Not sure if it still is.
| finiteseries wrote:
| The Xeelee Sequence also features post-post-posthumans designed
| to live on a neutron star in one of the books about midway
| through.
|
| My favorite "people" from the series, second only to the Roman
| Catholic eusocial human hives of course.
|
| Truly the largest series I've ever read in scope, if you can
| make it past the terribad writing & characterization in the
| first books (and you will, the ideas are worth it) it quickly
| gets better.
|
| https://en.m.wikipedia.org/wiki/Xeelee_Sequence
| Florin_Andrei wrote:
| Writing is pretty dry, but the ideas are grand. It's worth a
| read.
| bookofjoe wrote:
| A supreme triumph of the imagination. I'm going to reread it
| now that it's been brought to my attention here.
| sjclemmy wrote:
| I'm currently reading Flux. Brilliantly bonkers.
| Florin_Andrei wrote:
| Life on a neutron star, as understood by a local, in their own
| terms. It's brilliant.
| emtel wrote:
| Why do neutron stars have "crusts", as opposed to behaving more
| like a liquid?
| ars wrote:
| Because the pressure on the surface is only from one side.
|
| It's exactly like surface tension in water.
| emtel wrote:
| I don't think that's what causes surface tension in water.
| However, it turns out that surface tension is more mysterious
| than I thought.
|
| I thought surface tension was caused by inter-molecular
| attraction due to water being a polar molecule, which
| seemingly wouldn't apply to a neutron star.
|
| But this thread
| https://physics.stackexchange.com/questions/2615/are-
| there-a... contains a reply saying that surface tension is an
| inevitable result of the interface between two materials, and
| there are no liquids (even superfluids, apparently) that
| don't have surface tension.
|
| In any case I don't see why we'd expect condensed matter
| physics to be generalizable to neutronium...
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