
Most Massive Neutron Star Ever Detected - QueensGambit
https://greenbankobservatory.org/most-massive-neutron-star-ever-detected/
======
antognini
Back when I was an undergrad in astrophysics one of my professors claimed that
neutron stars are the most difficult objects to model in the universe. I
believe him. In order to have a good model of a neutron star you need to use
pretty much every branch of physics: general relativity, quantum field theory
(both QED and QCD), fluid dynamics, and statistical mechanics. And these
fields have important open questions in exactly the domains that you need to
apply them. So you end up needing to solve not just one open problem, but a
whole bundle of them, and they all conspire to work together to make each one
harder than it would be on its own.

Consequently, not very much is actually known about neutron stars. One of the
most important open problems in modeling neutron stars is just coming up with
the most basic relationship you can, namely the "equation of state." This is
simply a relationship between the density and the pressure within the neutron
star. The equation of state of normal stars was effectively developed in the
19th century with the development of statistical mechanics. The equation of
state of white dwarfs was developed by Chandrasekhar in the 1930s, not long
after the development of quantum mechanics (and while Chandrasekhar was on a
boat traveling from India to England!). But the equation of state for neutron
stars is still unknown.

A major consequence of the equation of state is that it predicts the maximum
mass of the object. In the case of a white dwarf, Chandrasekhar showed that
the equation of state implied that the maximum mass had to be about 1.44 times
the mass of the Sun (this is now appropriately known as the Chandrasekhar
limit). But because the equation of state of neutron stars is not known, it is
not known what the maximum mass of a neutron star is. Therefore, discovering
more massive neutron stars is very important because it can possibly rule out
certain equations of state. This, in turn, tells us a little bit more about
what physical processes are going on in the neutron star.

Since the problem is so theoretically intractable astrophysicists usually have
to neglect or simplify certain aspects of the physics considerably. If the
equation of state that comes out of these assumptions can be ruled out, this
means that one of these assumptions must be faulty, and some of the underlying
physics that was neglected turns out to be important after all.

~~~
oddthink
I worked on pulsars in grad school, and I always groused that I had to deal
with ultrarelativistic plasma physics and pair-production in curved spacetime.
There's a reason it's hard to come up with solid answers for these things.

~~~
ncmncm
Has anybody worked out yet how the polar "jets" work, or how they stay
collimated over light years distant? How precisely would particle ejected need
to be aimed to still be nearby other particles out that far? What could
provide such precision?

~~~
oddthink
For radio pulsars, I didn't think it was that mysterious. (Not like accretion-
powered things, where I don't know how that works.) You've got an intense
magnetic field that beams emission. At the low level any moving matter is
pinned to a field line, like a bead on a wire, and that sets the direction.

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_Understated_
Astronomical calculations never cease to amaze me.

I am the biggest astronomy nerd and watch loads of TV shows about it (the only
thing apart from dinosaur stuff that I watch on TV actually!) and when
scientists talk about the numbers involved in stellar objects it still blows
my mind every time.

"Just a single sugar-cube worth of neutron-star material would weigh 100
million tons here on Earth, or about the same as the entire human population"

I struggle to visualize that...

On a side note, "'Neutron stars are as mysterious as they are fascinating',
said Thankful Cromartie..." \- Possibly the coolest name I've ever heard :)

~~~
throwaway_law
>I struggle to visualize that...

Scales are simultaneously intuitive and yet mind bending. Never ceases to
amaze me either.

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SiempreViernes
Seems the PR people got the most important figure wrong, the measured mass is
2.14 +0.1 -0.09 M_sun, as per the preprint (and nature abstract[1]):
[https://arxiv.org/abs/1904.06759](https://arxiv.org/abs/1904.06759)

The 2.17 M_sun figure is instead the hypothesised _upper limit_ on the neutron
star mass, derived from the equations of state that survive recent LIGO
observations.

[1]:
[https://www.nature.com/articles/s41550-019-0880-2](https://www.nature.com/articles/s41550-019-0880-2)

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Tepix
This neutron star would probably collapse into a black hole, but its fast
rotations prevents it from doing so. It's like the movie "Speed", just with
higher stakes...

~~~
QueensGambit
How does this work? Is it the centrifugal force?

~~~
johndunne
The more correct term is angular momentum. There are 'mechanisms' that can
slow the angular momentum. Angular momentum is conserved, and as the star
collapses from the original total mass/radius to its new much lower radius,
resulting in a high spin rate. At some point the angualar momentum (or
centrifugal force) perhaps will fall to some critical value where the star
collapse further. I think this would be a valuable event in terms of figuring
out the equation of state and the related unanswered questios the PO
mentioned? It's been years since I studied phyisics at uni.... astronomy was
always me fav.

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_Understated_
Here's something that just popped into my head: If we could instanly beam a
sugar-cube of Neutron Star material to earth (using the same measurements as
in the article) what would happen to it?

Would it just fall right through whatever it's sat on or would it instantly
expand into something less dense?

~~~
kmm
With the confining pressure of gravity gone, it would instantly and violently
expand. The intense 10^32 pascals of degeneracy pressure drop quickly with
expansion, but even just assuming it can expand 5 ml at that pressure, the
energy released would be 5e26 joules. That's about 1000 times the asteroid
that made the dinosaurs extinct. It would certainly imply the end of all
multicellular life.

If somehow you could keep it confined, it would drop through whatever it was
put on, through the entire Earth, and pop up at the other side. I suppose it
would keep oscillating and eventually settle in the core.

~~~
_Understated_
Blimey. So I'd probably not even notice someone had teleported it here in the
first place as I blinked out of existence :)

Ok, on that note... what would it expand as? I mean, would it be a physical
substance, like particles of something like a gas or a plasma?

I assume it'd be quite hot (putting it mildly!)

~~~
jerf
It will cool into conventional matter eventually, but it would pass through a
lot of exotic phases in between. I'm not sure we can even _really_ answer that
question, but here's something to give you an idea of what I mean:
[https://en.wikipedia.org/wiki/Quark%E2%80%93gluon_plasma](https://en.wikipedia.org/wiki/Quark%E2%80%93gluon_plasma)
I'm not sure it would necessarily pass through that, but it would at least
make a decent pass at it in those first few nanoseconds.

If kmm's guesstimate of 5e26 joules is accurate, we're well beyond
"extinguishing multicellular life" and in the realm of eliminating Earth
entirely, which requires a minimum of 5.97e24 joules:
[https://en.wikipedia.org/wiki/Gravitational_binding_energy](https://en.wikipedia.org/wiki/Gravitational_binding_energy)
1% efficiency of transfer to the Earth is probably attainable.

~~~
kmm
I think you might have mistaken the Earth's mass in kg with the gravitational
binding energy. That last one is 2.5e32 J. So about a millionth of the neutron
sugar cube.

~~~
jerf
facepalm Urf, I was right the first time. Oh well.

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QueensGambit
This newly detected neutron star is 333,000 times the mass of the Earth and
2.17 times the mass of the sun. But the star is only about 15 miles across.
This is close to the limit of how much mass a compact object can contain
before it crushes itself into a black hole.

~~~
Gibbon1
> This is close to the limit of how much mass a compact object can contain
> before it crushes itself into a black hole.

Obviously it's time for bed because reading this makes me want to toss a
quarter in it to see what happens.

~~~
arethuza
Assuming you are starting from orbit wouldn't you have to give that coin quite
a "toss" to get it to change its orbit so as to hit the surface? No atmosphere
to help...

~~~
saagarjha
Not if you’re far enough away.

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sidcool
How come we know what a neutron star is made up of but do not know what's
inside black holes? A genuine question...

~~~
SiempreViernes
That's not quite right, we do know what black holes are made up of: the
remains of a star. Well, if they are reasonably small they are made out of the
remains of _a_ star, if they are too big they can contain the remains of lots
of stars and also gas, dust and maybe bits of planets, but exactly how we get
the biggest black holes isn't clear.

The issue is rather that we don't know what all that star stuff _becomes_ once
it goes into the black hole, though there are theories. The problem is that
the defining feature of a black hole, its even horizon, by necessity means
there is no way of knowing what theory is correct since nothing happening
inside is supposed to matter to us.

So before we can make any real progress on the interior of black holes we thus
need to figure out exactly in what sense the event horizon leaks information,
if it does.

In contrast, while we don't _really_ know what happens to matter inside a
neutron star, its surface remains visible to us and so we have been able to
discard many different theories about what goes inside it. There is still
debate about the precise equation of state, which correspond to different
internal structure the various models represent and so different ideas of how
a neutron star is made up.

Honestly, I don't know how much difference there are between the various
models, but pretty crazy sounding ideas are still popping up, so there must be
at least _some_ space left.

~~~
posterboy
I once figured, could most massive stars have a black hole at the center? With
thr crazy time dilations around a BH, I imagine the implosion would capture
the escaping image of the prior star. I imagine a microscopic black hole at
the core of thessun that immediately evaporates, but immediately looks like an
eternity for us

~~~
SiempreViernes
No, you need something releasing a lot of energy in the middle of a star,
otherwise it collapses down on itself and stops being a star, the event
horizon doesn't provide any supporting pressure.

Also, the process that compresses matter to the point it collapses to a black
hole is very destructive; there is no reasonable way to _form_ a black hole in
the middle of the star.

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sytelus
It's only 4600 light years away. If it collapses in to blackhole, it would be
the closest blackhole to the earth? In few 10s of thousands of year, can it
devour solar system?

~~~
pnako
Its mass would not change, so it should not affect other objects more than it
does at the moment (I think).

~~~
GistNoesis
Not a physicist, but isn't the whole point of black hole that they can grow.

The way I picture it, is once you reach the black-hole state, there is a
regime change which make it more easy to gulp matter in. I guess how big and
how fast it grows depends how much mass there is nearby to concentrate.

Once formed they tend to an equilibrium with their surrounding dictated by the
balance mass-in/evaporation-out.

~~~
SiempreViernes
Not really: (stellar) black holes have less mass than whatever object they
were born from, and the mass is the only way by which they interact with
matter.

It's true that they don't have a stellar wind that pushes gas away, but they
are born in the void left by their progenitor star, and once they start
accreting there will be radiation pushing things again.

~~~
Retric
That accretion disk represents constant growth via new mass.

So, either way the black hole is is sucking up mass faster than a star.

~~~
SiempreViernes
No, most black holes have _no_ visible accretion, and of those that have _all_
have _variable_ emission, meaning variable accretion rates.

Black holes are _not_ constantly growing.

~~~
Retric
We are not talking about rapid growth but...

Hawking radiation for a 1 solar mass black hole represents less than 1 atom of
material lost per billion years (~10^67 years vs ~10^57 atoms) They gain more
than that even without a noticeable accretion disk inside our current galaxy.

It’s only very very long time frames after black holes collect this material
that they start losing mass on average.

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hi41
The article refers to a neutron star being a giant atomic nuclei. How did this
happen? The mass of the neutron star and the star before the collapse are
similar. so why did the matter change into atomic nuclei? This makes me think
that gravity is not the only thing at play here; density also matters. Is my
this correct? So, is gravity dependent on the density? I guess I am confused.

~~~
Ancalagon
The mass of the neutron star is _not_ the same as the entire star before it.
The neutron star is (mostly) core material from its parent star, the rest of
the matter was likely flung out upon that stars death. Gravity is not the only
thing at play, strong nuclear forces between atoms prevent the star from
collapsing under its own gravity, as well as the angular momentum of the stars
spin. The neutron star is one giant atomic nuclei in the sense that all of its
atoms are incredibly densely packed together. Imagine a styrofoam ball that
you put under immense pressure from all angles (say by putting it deep under
water). The air/free space in the styrofoam is squeezed out, and this in a
sense is the same thing that happens to the plasma inside the parent star's
core as it collapses. All of the atoms are squeezed together, and a balancing
act is created whereby the incredible density of the core is trying to pull
the matter inwards (into a black hole), while the strong nuclear
force/momentum are pushing back to prevent the star from collapsing further.

~~~
hi41
Thank you for the explanation.

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imvetri
Can the mass density of atom's nuclei match such kind of object ?

On a scale of atom, this star and black hole what would be the mass density ?

~~~
oddthink
It's about nuclear density. Neutron stars are held up by neutron degeneracy
pressure.

Another fun fact is that the magnetic field energy density alone near the
surface of a pulsar (1e12 gauss and up) is about that of lead. (~40 g/cm^3).

~~~
ttul
What does that even mean in any sort of a human-relatable way? What would
happen to your body in the presence of such a strong magnetic field?

~~~
oddthink
Atoms don’t work in that kind of a field, let alone molecules. Nothing wants
to go across field lines, just along them.

------
known
A matchbox sized neutron-star would weigh 3 billion tons.
[https://clearlyexplained.com/neutron-
stars/index.html](https://clearlyexplained.com/neutron-stars/index.html)

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duxup
Can anyone describe why Neutron stars are more mysterious / confusing than say
a black hole?

A black hole seems to be just the next "step" in terms of something super-
massive, but then why are neutron star's more of a mystery?

~~~
antognini
The main reason is that while black holes are more "extreme" objects, they are
actually physically very simple. The matter collapses to a singularity (as far
as we know), and so the physics is just described by the Einstein field
equations with a correction for quantum fluctuations near the event horizon.
Remarkably, the entire state of the black hole can be described by only the
mass, charge, and angular momentum of the black hole.

By contrast, although neutron stars are less "extreme", they end up in a
regime where the physics becomes much more difficult. The gravity is strong
enough that you still need general relativity, but because the object is
extended rather than a singularity, there's also a bunch of "stuff" which
needs to be described as well. This means that you need to add in quantum
electrodynamics and quantum chromodynamics. Furthermore, it's thought that at
these densities you end up with some sort of a superfluid which means you need
fluid dynamics and statistical physics to model its behavior, all of which is
extremely difficult.

That said, there is another sense in which we could say that black holes are
actually more mysterious than neutron stars. Although the physics of neutron
stars is very complicated, we at least know what all the fundamental equations
are. In the case of black holes if we want to understand physics near the
singularity we would need a theory of quantum gravity which we currently don't
have.

~~~
PorterDuff
Is there some reason for all neutron stars to have the same physical make-up
and internal behavior? or could they fall into types?

~~~
antognini
It is entirely possible that there could be different types of neutron stars,
although the same physics will describe them all. As an analogy, white dwarfs
all have the same equation of state, but based on the mass of the white dwarf
the electrons can either be relativistic or non-relativistic. (This is not
really a true dichotomy, it's just a spectrum.) There could plausibly be
something similar with neutron stars.

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ncmncm
Half the pulsars we see could be this big, or even bigger. This is just a rare
one they could measure.

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ijiiijji1
3.375e10 kg/cc

