I How Does the Size of Neutron Stars Compare to Black Holes?

[davLev]

In the following article it is stated:

https://skyandtelescope.org/astronomy-news/measuring-neutron-stars-exactly/

"We're seeing the gas whipping around just outside the neutron star's surface," said Edward Cackett (University of Michigan), in a press release. "And since the inner part of the disk obviously can't orbit any closer than the neutron star's surface, these measurements give us a maximum size of the neutron star's diameter. The neutron stars can be no larger than 18 to 20.5 miles across [29 to 33 kilometers], results that [confirm] other types of measurements."
Both groups examined spectral lines of X-ray emission from iron atoms in superhot gas that's orbiting at about 40% of light speed just above the neutron stars' surfaces.

Therefore, we see the disc of a hot gas which spins around the Neutron star at almost 40% of the speed of light. (or 0.4 c).
Based on that observation we understand that The neutron stars can be no larger than 18 to 20.5 miles across

Hence, this measurement represents the maximal size of the Neutron star, but what about the minimal size?
Why do we assume that it represents the real diameter of the Neutron star?

Let's compare that observation to a BH.
https://en.wikipedia.org/wiki/Messier_87

The visible material around the black hole rotates mostly clockwise with respect to the observer, which due to the direction of the axis of rotation causes the bottom part of the emission region to have a component of velocity toward the observer.[86] The rotation parameter was estimated at �=0.9±0.1 , corresponding to a rotation speed ≈ 0.4 c.[87]

https://en.wikipedia.org/wiki/Messier_87#/media/File:Black_hole_-_Messier_87_crop_max_res.jpg

It was a surprise for me to discover that the hot gas disc around both objects spins exactly at 0.4 c.

I wonder why that Hot gas disc is called an accretion disc when it spins around a BH at 0.4c, but there is no specific name for a hot gas disc when it spins around the Neutron star at also 0.4c?

Why the hot gas disc can give us an indication for the Neutron star' diameter but no indication for a BH' diameter?

Why do we assume that at the same mass, the diameter of a Neutron star is significantly bigger than a BH?

 

[Tom.G]

Why do we assume that at the same mass, the diameter of a Neutron star is significantly bigger than a BH?

You may have heard of Gravitational Lensing. That is when light is passing close enough to a large mass that the light is re-directed, much as a glass lens or a prism bends light.

If the same mass is concentrated to a small point, the gravitational field stays pretty much the same at a distance... however, with the gravity field concentrated to a small surface, the field intensity at the surface is very high.

A Black Hole is named that because the gravitational force at its surface is so strong that any light (emitted or passing close-by) can not escape.

See:
https://www.google.com/search?&q=schwarzchild+limit

Hope this helps.
Cheers,
Tom

 

[davLev]

You may have heard of Gravitational Lensing. That is when light is passing close enough to a large mass that the light is re-directed, much as a glass lens or a prism bends light.

If the same mass is concentrated to a small point, the gravitational field stays pretty much the same at a distance... however, with the gravity field concentrated to a small surface, the field intensity at the surface is very high.

Thanks Tom

Where the idea of a small surface came from?

Gravitational lensing works for BH and also for galaxy:
https://facts.net/nature/universe/9-mind-blowing-facts-about-gravitational-lensing/

"Gravitational lensing is a captivating phenomenon in the Universe that has fascinated scientists and space enthusiasts for decades. It occurs when the path of light from a distant object is distorted by the gravitational field of a massive object, such as a galaxy or a black hole."

The diameter of a galaxy could be more than 100,000 LY.
Hence, do you agree that there is no need for a small surface in order to get the Gravitational lensing phenomenon?

A Black Hole is named that because the gravitational force at its surface is so strong that any light (emitted or passing close-by) can not escape.

We can't see a BH and we can't see a Neutron star (assuming that there is no hot gas around it).
Therefore, why do you claim that the Gravitational lensing can work for the BH but not for the same mass Neutron star?
Would you kindly direct me to the relevant article?

 

[PeterDonis]

Why do we assume that it represents the real diameter of the Neutron star?

Why do you think anyone is making that assumption?

 

[Tom.G]

I put in a HELP request to get some real experts here to help you with your study.

My background is mainly electronics and I've only looked at the astrophysics out of curiosity many years ago.

Cheers,
Tom

 

[PeterDonis]

It was a surprise for me to discover that the hot gas disc around both objects spins exactly at 0.4 c.

Nobody said "exactly". Both measurements are approximate. Both quotes that you give explicitly say so.

I wonder why that Hot gas disc is called an accretion disc when it spins around a BH at 0.4c, but there is no specific name for a hot gas disc when it spins around the Neutron star at also 0.4c?

The term "accretion disc" was adopted for hot gas around black holes because it is falling into the hole, increasing the hole's mass. Unless there is a constant source of more gas, the hot gas around a black hole eventually disappears as it has all fallen into the hole.

From what I understand, this doesn't happen with neutron stars, at least not to anything like the same extent. Some of the hot gas might accrete onto the star, but because the star has an actual surface and is not vacuum like a black hole, the gas can't just fall in.

Why the hot gas disc can give us an indication for the Neutron star' diameter but no indication for a BH' diameter?

We can calculate the area of a black hole's horizon exactly if we know its mass and its spin rate. We can't do that for neutron stars because, unlike black holes, not all neutron stars with the same mass and spin rate are identical.

Why do we assume that at the same mass, the diameter of a Neutron star is significantly bigger than a BH?

We don't assume this. We know it from the laws of general relativity. A neutron star is in hydrostatic equilibrium, supporting itself against its own gravity by internal pressure. Any object like that cannot have a radius smaller than 9/8 of the Schwarzschild radius of a black hole with the same mass. (And in fact our models of neutron stars predict that they will be a fair bit larger than this minimum size.) So there is a finite size gap between black holes and neutron stars.

 

[PeterDonis]

why do you claim that the Gravitational lensing can work for the BH but not for the same mass Neutron star?

I'm not sure @Tom.G was saying that. Gravitational lensing does work for neutron stars.

 

[mfb]

Hence, this measurement represents the maximal size of the Neutron star, but what about the minimal size?
Why do we assume that it represents the real diameter of the Neutron star?

We don't.

It was a surprise for me to discover that the hot gas disc around both objects spins exactly at 0.4 c.

It's not a coincidence. For a given mass you have an innermost stable circular orbit(technically more if the object rotates but let's ignore that here). Everything closer to the central object will hit the central object or escape quickly, so the innermost (fastest) matter we see comes from that orbit. It doesn't depend on the size or type of the central object, as long as it's smaller than the radius of that orbit.

The fact that we see it for that neutron star tells us the neutron star has to be smaller. This is useful information because neutron stars are complex objects that we can't model well.
The fact that we see it for M87 tells us that the black hole has to be smaller. This doesn't get any attention because we can calculate the radius from general relativity anyway.

 

[davLev]

The fact that we see it for that neutron star tells us the neutron star has to be smaller. This is useful information because neutron stars are complex objects that we can't model well.
The fact that we see it for M87 tells us that the black hole has to be smaller. This doesn't get any attention because we can calculate the radius from general relativity anyway.

Thanks for your message.
M87 is a Black hole.
So, how do we know if the object is BH or neutron star (assuming that they have the same mass)?
In the following article there is a nice description for those objects:

https://flexbooks.ck12.org/cbook/ck...y/lesson/neutron-stars-and-black-holes-ms-es/

Neutron Stars​

After a supernova explosion, the star's core is left over. This material is extremely dense. What happens next depends on the core's mass. The core might be less than about four times the mass of the sun. In this case, the star will become a neutron star. A neutron star (Figure below) is made almost entirely of neutrons. A neutron star has more mass than the sun; yet, it is only a few kilometers in diameter.

Black Holes​

The core remaining after a supernova could be more than about five times the mass of the sun. In this case, the core collapses to become a black hole. Black holes are unimaginably dense. Not even light can escape their gravity (Figure below)! This is why they are black. We can't see black holes.

It is stated: We can't see black holes.
Do they mean that we can see a Neutron star core?
If we can't see, then why are we so sure that after the supernova explosion, the star's core that is left is a Neutron star (at any mass)?
Why we can't just assume that we get a BH?
In other words, how do we know if the object is neutron star or BH if we can't see the core of none of them?

 

[PeterDonis]

how do we know if the object is BH or neutron star

All types of compact objects other than black holes (white dwarfs, neutron stars, as well as "quark stars" and other hypothesized such objects) have a maximum mass. Any compact object more massive than the largest such maximum mass (which is not more than 3 solar masses; we don't know the exact value but we know it's not more than that) must be a black hole.

 

[PeterDonis]

why are we so sure that after the supernova explosion, the star's core that is left is a Neutron star (at any mass)?

We aren't; it can only be a neutron star if its mass is less than the maximum mass for neutron stars.

 

[.Scott]

If you can determine that the speed of a distance object is steady, then you can determine that the orbit is roughly circular. If you know its circular and can measure its speed and period, then you can calculate the mass of the object being orbited (the star, NS, or BH).

When that object is a BH, you can also immediately calculate its diameter. So using the orbit as a "maximum diameter" is not very useful for black holes.

 

[davLev]

We aren't; it can only be a neutron star if its mass is less than the maximum mass for neutron stars.

Thanks

In the following article it is stated that the maximal size of the Neutron star is 2.16 Solar mass.

https://www.sciencedaily.com/releases/2018/01/180116093650.htm

Whilst most neutron stars have a mass of around 1.4 times that of the sun, massive examples are also known, such as the pulsar PSR J0348+0432 with 2.01 solar masses.

The density of these stars is enormous, as if the entire Himalayas were compressed into a beer mug.

Together with his students Elias Most and Lukas Weih, Professor Luciano Rezzolla, physicist, senior fellow at the Frankfurt Institute for Advanced Studies (FIAS) and professor of Theoretical Astrophysics at Goethe University Frankfurt, has now solved the problem that had remained unanswered for 40 years: With an accuracy of a few percent, the maximum mass of non-rotating neutron stars cannot exceed 2.16 solar masses.

It is also stated that:

However, there are indications that a neutron star with a maximum mass would collapse to a black hole if even just a single neutron were added.

Therefore, if the star is very massive, then after its Supernova, why we can't expect to get a Black Hole instead of Neutron star?

So, how do we know that after the supernova we should get a Neutron star?

In the following article it is stated that:

https://en.wikipedia.org/wiki/Magnetar
A magnetar is a type of neutron star with an extremely powerful magnetic field (~109 to 1011 T, ~1013 to 1015 G).[1] The magnetic-field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays.[2]

However, how do we know that in the core of any magnetar/pulsar there is a neutron star?
What kind of observation convince us that magnetar/pulsar must be based on a neutron star and not on Black hole?

 

[Ibix]

Therefore, if the star is very massive, then after its Supernova, why we can't expect to get a Black Hole instead of Neutron star?

We do expect that. Smaller ones leave neutron stars, larger ones leave black holes.

What kind of observation convince us that magnetar/pulsar must be based on a neutron star and not on Black hole?

Black holes can only have magnetic fields if they're electrically charged. We simply don't see macroscopic charged matter out there - it attracts charges of the opposite sign and neutralises itself very rapidly.

 

[PeterDonis]

In the following article it is stated that the maximal size of the Neutron star is 2.16 Solar mass.

The article does not specify whether this limit is for non-rotating neutron stars, but I suspect it is. Rotating neutron stars will have a somewhat larger maximum mass limit that depends on the rate of rotation. Most neutron stars that we observe are rotating pretty rapidly.

 

[PeterDonis]

Black holes can only have magnetic fields if they're electrically charged.

More precisely, black holes surrounded by vacuum can only have magnetic fields if they are electrically charged.

Rotating black holes surrounded by accreting matter, however, can have magnetic fields anchored in the matter.

 

[mfb]

So, how do we know if the object is BH or neutron star (assuming that they have the same mass)?

If it's close enough, we look for radiation emitted by a neutron star. If that doesn't exist, it's a black hole.

For objects far away we measure the mass - if it's light it has to be a neutron star, if it's heavy it has to be a black hole, in between we can't be sure.

 

[PeterDonis]

if it's light it has to be a neutron star

To be clear, we believe this not because there is a theoretical minimum mass for a black hole (there isn't), but because we are only considering the possibility of black holes forming from collapse of massive stars, and such a collapse process will only form a black hole if there is too much mass for a neutron star.

 

[davLev]

If it's close enough, we look for radiation emitted by a neutron star. If that doesn't exist, it's a black hole.

What do you think about M87?

https://link.springer.com/chapter/10.1007/978-94-010-3311-4_16
This paper reports upon an observation of hard X-radiation from the direction of M87.

It is a BH and it has radiation.

Black holes can only have magnetic fields if they're electrically charged.

More precisely, black holes surrounded by vacuum can only have magnetic fields if they are electrically charged.

I don't understand why black holes surrounded by vacuum can only have magnetic fields if they are electrically charged, while Neutron star have magnetic fields even if isn't electrically charged?

We must understand the difference of the internal structure between BH to Neutron star.
Therefore, let's start with the supernova:

https://en.wikipedia.org/wiki/Supernova

A supernova (pl.: supernovae or supernovas) is a powerful and luminous explosion of a star. A supernova occurs during the last evolutionary stages of a massive star, or when a white dwarf is triggered into runaway nuclear fusion. The original object, called the progenitor, either collapses to a neutron star or black hole, or is completely destroyed to form a diffuse nebula.

Neutron star -
We start the process with a star:

https://www.mccc.edu/~dornemam/Planet_Walk/Sun/the_sun.htm

The Sun is a typical star, and is also the star that is nearest to the Earth. It is composed of a mixture of 73% hydrogen, 25% helium, and 2% other elements by weight.

Hydrogen contains one proton and no neutrons - 73%

Helium contains two protons and two neutrons - 25%

Let's ignore the other elements - 2%.

So, out of 98 atoms in the Sun, there are:

Protons - 73 * 1 + 25 * 2 = 123
Neutrons - 25* 2 = 50.

For each neutron there are about 123/50 = 2.5 protons.

As there are much more protons than neutrons in a star, then why do we call it Neutron star instead of Proton star?

Neutron: Composition - 1 Up quark, 2 Down quarks + gluons
Proton: Composition - 2 Up quark, 1 Down quarks + gluons

Do we know how all of those protons are immediately converted to Neutrons during the supernova impact?

Black hole -
We assume that a black hole could be created directly by the supernova (If the star is very massive) or it could be created from a Neutrons star.
https://www.sciencedaily.com/releases/2018/01/180116093650.htm
However, there are indications that a neutron star with a maximum mass would collapse to a black hole if even just a single neutron were added.

Let's try to verify what could be the outcome if we add a single Neutron to a neutron star with a maximum mass?
Do you agree that in this case the internal gravity pressure / temp is so strong/high that it breaks the neutron/proton (Hardon) and take out the gluons which holds the 3 quarks together?

Therefore, we get quarks and gluons.
However, can those elements exist at the core of the BH while they aren't bound together in the hardon?
Do you agree that quarks are particles?
Therefore, technically they could survive in the core and their mass would count.
Never the les, the Gluons isn't a particle.

Therefore, it can't exist outside the hardon.
So, what is the outcome of the gluons once it is ejected from the Hardon?
Any idea how the gluons could keep its mass outside the Hardon?

Please be aware that the gluons contribute 99% of the Hardon mass.

If the gluons can't keep its mass outside the Hardon, then do you agree that its mass must be converted into energy (based on Einstein formula).

If that is correct, then once the Neutron star collapse, 99% of its mass (all the broken gluons) should immediately transformed into severe energy while only 1% (all the quarks) could exist.

Is it realistic?
Did we ever observed a Neutron star as it collapse?

Could it be that we miss something in our theories about BHs and Neutron stars?
It is stated:
The original object, called the progenitor, either collapses to a neutron star or black hole,
So, could it be that The original object, called the progenitor, should always collapse into dense quark core (call it as you wish)?
However, the key obstacle for this idea is:

Could this dense quark core have magnetic fields even if isn't electrically charged?

 

[PeterDonis]

we look for radiation emitted by a neutron star. If that doesn't exist, it's a black hole.

You have to be careful here. Black holes can have accretion disks that emit radiation.

It is a BH and it has radiation.

See above.

 

[PeterDonis]

We must understand the difference of the internal structure between BH to Neutron star.

Yes, indeed, and you apparently do not.

A neutron star is an object made of matter whose structure is determined by hydrostatic equilibrium under its own gravity.

A black hole is not made of matter; it is vacuum. It has no "internal structure". It is pure spacetime geometry. When an object collapses to a black hole, the matter in the object falls below the horizon and, according to classical GR (which is what we are using here), hits the singularity at $r = 0$ and is destroyed, leaving nothing behind but spacetime geometry.

The rest of your post ignores this crucial distinction.

Could it be that we miss something in our theories about BHs and Neutron stars?

No. You just need to improve your understanding of them.

 

[PeterDonis]

Let's try to verify what could be the outcome if we add a single Neutron to a neutron star with a maximum mass?
Do you agree that in this case the internal gravity pressure / temp is so strong/high that it breaks the neutron/proton (Hardon) and take out the gluons which holds the 3 quarks together?

No. That's not what happens.

What happens is that the neutron star, if it accretes enough mass to go above the maximum mass for a neutron star, is unable to maintain hydrostatic equilibrium and starts collapsing. This has nothing whatever to do with "breaking" neutrons or "taking out gluons". It's just a loss of hydrostatic equilibrium leading to collapse.

 

[PeterDonis]

dense quark core

Please give a reference for this.

 

[davLev]

What happens is that the neutron star, if it accretes enough mass to go above the maximum mass for a neutron star, is unable to maintain hydrostatic equilibrium and starts collapsing. This has nothing whatever to do with "breaking" neutrons or "taking out gluons". It's just a loss of hydrostatic equilibrium leading to collapse.

Please see the following:

https://www.space.com/supermassive-black-holes-surprising-link-gluon

Supermassive black holes share a surprising link with subatomic gluon 'color glass walls'​

CGCs are created when atomic nuclei are accelerated to near the speed of light and then slammed together. After these collisions, conducted at facilities such as the Relativistic Heavy Ion Collider in Upton, New York, the CGCs "melt" to form a nearly perfect liquid of quarks and gluons.

the team found that gluons appear to organize themselves in a way that conforms to a universal limit on the amount of entropy, or disorder, that can exist in a system. The enormous conglomerates of gravitons that make up black holes are also believed to arrange themselves according to this limit.

This mathematical similarity suggests there is a correspondence between how black holes are born, reach thermal equilibrium with their environment and even how they may eventually decay, and how walls of gluons collide in nuclear collisions at near-light speeds.

In both systems, the bosons are arranged in the most energy- and size-efficient configuration. This creates a high degree of order that is typical of both CGCs and black holes, with both systems packing in the maximum amount of quantum information possible about their constituent bosons , including their spatial distribution, velocity and collective forces.

Do you confirm that in any star there must be significantly more protons than neutrons?
If so, Would you kindly explain why a Neutron star doesn't called proton star?

 

[davLev]

You have to be careful here. Black holes can have accretion disks that emit radiation.

Please be aware that Neutron stars also have disks:

https://skyandtelescope.org/astronomy-news/measuring-neutron-stars-exactly/

"We're seeing the gas whipping around just outside the neutron star's surface," said Edward Cackett (University of Michigan), in a press release. "And since the inner part of the disk obviously can't orbit any closer than the neutron star's surface, these measurements give us a maximum size of the neutron star's diameter. The neutron stars can be no larger than 18 to 20.5 miles across [29 to 33 kilometers], results that [confirm] other types of measurements."

So why we can't claim that this Neutron star' disc emits radiation?

 

[davLev]

Black hole or neutron star?​

https://www.psu.edu/news/research/story/black-hole-or-neutron-star/

For decades, astronomers have been puzzled by a gap in mass that lies between neutron stars and black holes: the heaviest known neutron star is no more than 2.5 times the mass of our sun, or 2.5 solar masses, and the lightest known black hole is about 5 solar masses. The question remained: Does anything lie in this so-called mass gap?

Now, in a new study from the National Science Foundation's Laser Interferometer Gravitational-Wave Observatory (LIGO) and the European Virgo detector, scientists have announced the discovery of an object of 2.6 solar masses, placing it firmly in the mass gap.

"We've been waiting decades to solve this mystery," said Vicky Kalogera, a professor at Northwestern University. "We don't know if this object is the heaviest known neutron star, or the lightest known black hole, but either way it breaks a record."

So, could it be that we miss something in our understanding about Neutron star and BH?

 

[davLev]

Please give a reference for this.

A quark star may have just been discovered​

https://www.advancedsciencenews.com/a-quark-star-may-have-just-been-discovered/

a recent discovery may point toward the existence of a new type of star: the quark star.

The hypothesized existence of such objects was first expressed in 1965 by Soviet physicists Dmitri Ivanenko and Dmitri Kurdgelaidze. The idea is based on the assumption that at extreme pressures in the collapsed cores of stars, neutrons become so compressed that they breakdown into the elementary particles that make them up, called quarks. Under this intense gravity and strong interaction, though free, quarks clump together, forming a quark star.

 

[PeterDonis]

Please see the following

That source is based on a speculative hypothesis about quantum gravity. It is not saying that black holes are made of matter the way neutron stars are.

Please be aware that Neutron stars also have disks

That's true, they can. I never said otherwise.

why we can't claim that this Neutron star' disc emits radiation?

I never said we can't. I was pointing out (to @mfb, not you) that since black holes can have accretion disks that can emit radiation, we cannot say that if we detect radiation, the object cannot be a black hole. Nobody has said that if we detect radiation, the object cannot be a neutron star.

could it be that we miss something in our understanding about Neutron star and BH?

Not the part of that understanding that you are asking about, no. The "mass gap" referred to in the source you reference is not actually a problem at all; it's just a consequence of the fact that our observations are incomplete.

A quark star may have just been discovered

Nothing said in this article makes "quark stars" any less speculative than they were before. It's just a pop science article which, as is typical for pop science articles, overstates what the research it is describing actually shows.

Btw, so far you have not given a single reference that is an actual peer-reviewed paper. Nor, apparently, are you familiar with any of the literature that discusses things like the structure of neutron stars, such as Shapiro & Teukolsky. You cannot expect to learn actual science at the level you are trying to discuss it from pop science articles and middle school textbooks.

 

[davLev]

Would you kindly answer the following questions:

1. Do you confirm that in stars there must be more protons than Neutrons?

https://www.mccc.edu/~dornemam/Planet_Walk/Sun/the_sun.htm
The Sun is a typical star, and is also the star that is nearest to the Earth. It is composed of a mixture of 73% hydrogen, 25% helium, and 2% other elements by weight.
Hydrogen contains one proton and no neutrons - 73%
Helium contains two protons and two neutrons - 25%
Let's ignore the other elements - 2%.
So, out of 98 atoms in the Sun, there are:
Protons - 73 * 1 + 25 * 2 = 123
Neutrons - 25* 2 = 50.
For each neutron there are about 123/50 = 2.5 protons.

2. As there are much more protons than neutrons in a star, then why after the supernova we get a star which is mainly based on Neutrons and therefore it is called Neutron star? Why not Proton star?

3. How all/most of the protons in this star could instantly be transformed into Neutrons during the supernova impact?

4. Could it be that in Neutron star there are some protons and quarks. If so, at what ratio with regards to neutrons?

5. What kind of observations do we have that convinced us that Neutron star is mainly based on Neutrons?

 

[PeterDonis]

Do you confirm that in stars there must be more protons than Neutrons?

Generally one would expect that to be true as long as there is significant hydrogen in the star. But "star" is a more general term than you appear to think; see below.

Would you kindly explain why a Neutron star doesn't called proton star?

Um, because it's made of neutrons? The word "star" doesn't just mean "star like the Sun".

What kind of observations do we have that convinced us that Neutron star is mainly based on Neutrons?

The observations of their masses and sizes (as well as other data like pulsar timings) and our theoretical knowledge about possible states of matter for objects with those properties. For example, I have already referenced Shapiro & Teukolsky, a textbook which discusses this in great detail.

How all the protons in the star could instantly be transformed into Neutrons during the supernova impact?

They aren't "instantly" transformed. They are transformed during the process of collapse from an ordinary star to a neutron star. The density range during which this "neutronization" takes place (mostly by inverse beta decay) is discussed in detail in Shapiro & Teukolsky.

Could it be that in Neutron star there are some protons and quarks. If so, at what ratio with regards to neutrons?

Our neutron star models generally have a very thin layer of white dwarf-type matter at the surface, which would contain a roughly equal number of protons and neutrons. However, this layer is only a very small fraction (I think well under one percent) of the total mass of the neutron star.

Neutrons (and protons) are made of quarks, so of course there are quarks everywhere in a neutron star. If by "quarks" you mean some other state of quarks besides neutrons or protons, there are speculations along these lines, but no good evidence for any of them that I'm aware of.

 

[davLev]

Thanks for your prompt reply!

 

[davLev]

They aren't "instantly" transformed. They are transformed during the process of collapse from an ordinary star to a neutron star. The density range during which this "neutronization" takes place (mostly by inverse beta decay) is discussed in detail in Shapiro & Teukolsky.

I assume that Shapiro & Teukolsky have offered the idea for the formation of the Neutron stars.
However, any idea should be confirmed by some sort of evidence.

Neutrons (and protons) are made of quarks, so of course there are quarks everywhere in a neutron star. If by "quarks" you mean some other state of quarks besides neutrons or protons, there are speculations along these lines, but no good evidence for any of them that I'm aware of.

Yes, we have evidence:
In the following article it is stated:

Evidence for quark-matter cores in massive neutron stars​

https://ui.adsabs.harvard.edu/abs/2020NatPh..16..907A/abstract

The theory governing the strong nuclear force—quantum chromodynamics—predicts that at sufficiently high energy densities, hadronic nuclear matter undergoes a deconfinement transition to a new phase of quarks and gluons.
the matter in the interior of maximally massive stable neutron stars exhibits characteristics of the deconfined phase, which we interpret as evidence for the presence of quark-matter cores.

https://ncatlab.org/nlab/show/quark-gluon+plasma

The quark-gluon plasma is the phase of matter of quantum chromodynamics at extremely high temperature. At high temperature quarks are not confined to hadron bound states but propagate freely together with the gluons, forming a “quark-gluon soup”. Since this is analogous to an ordinary plasma which is a phase where electrons and protons are no longer bound to atoms but propagate freely, one speaks of quark-gluon plasma.

Therefore, we have evidence for quark-gluon matter/plasma in the core of a massive Neutron star.
This is a critical issue as it proves that the Hardon (neutron or protons) could break down to quarks and gluons.

Hence, is it acceptable to call those Neutron stars as quark-gluons stars?

 

[PeterDonis]

I assume that Shapiro & Teukolsky have offered the idea for the formation of the Neutron stars.

You shouldn't assume anything. You should go read Shapiro & Teukolsky.

However, any idea should be confirmed by some sort of evidence.

Um, Shapiro & Teukolsky is a classic textbook on white dwarfs, neutron stars, and black holes, which discusses the evidence about those objects, as well as the theoretical models that explain the evidence, in great detail.

Yes, we have evidence:

No, we have some particular physicists' interpretation of the evidence. It says so right in what you quoted:

the matter in the interior of maximally massive stable neutron stars exhibits characteristics of the deconfined phase, which we interpret as evidence for the presence of quark-matter cores.

Emphasis mine.

Hence, is it acceptable to call those Neutron stars as quark-gluons stars?

Not until standard terminology in the field does so. Which it hasn't.

 

[davLev]

Um, Shapiro & Teukolsky is a classic textbook on white dwarfs, neutron stars, and black holes, which discusses the evidence about those objects, as well as the theoretical models that explain the evidence, in great detail.

This textbook was published in 1983.

https://onlinelibrary.wiley.com/doi/book/10.1002/9783527617661
Black Holes, White Dwarfs, and Neutron Stars: The Physics of Compact Objects
Author(s):
Stuart L. Shapiro, Saul A. Teukolsky
First published:27 July 1983
Stuart Louis Shapiro is an American theoretical astrophysicist.

For me, evidence means observation.
I wonder what kind of observation Shapiro & Teukolsky have used to justify their theoretical astrophysics of Compact Objects?

In the following article it is stated:

https://www.forbes.com/sites/starts...collapse-to-form-black-holes/?sh=414c81c37159

The Surprising Reason Why Neutron Stars Don't All Collapse To Form Black Holes​

"In a shocking find, the average peak pressure, near the center of the proton, comes out to 10^35 pascals: a greater pressure than neutron stars experience anywhere."

Do you believe that 40 years ago Shapiro & Teukolsky have already new about this shocking evidence and they have used it in their theoretical concept?

Please add to that the spinning/rotating motion of the Neutron star:

Rotating neutron stars will have a somewhat larger maximum mass limit that depends on the rate of rotation. Most neutron stars that we observe are rotating pretty rapidly.

We know that the rotation of the Earth reduces gravity slightly at the equator as compared to the Poles.
If the rotation of the neutron star is almost at the speed of light, could it decrease dramatically the total gravity?

Based on the above facts, could it be that the mass of a Neutron star should be several times heavier than the expected 2 solar mass before it would collapse to Black hole?

With regards to black hole:
Let's assume that the object accretes enough mass to go above the maximum mass for a neutron star,

What happens is that the neutron star, if it accretes enough mass to go above the maximum mass for a neutron star, is unable to maintain hydrostatic equilibrium and starts collapsing. This has nothing whatever to do with "breaking" neutrons or "taking out gluons". It's just a loss of hydrostatic equilibrium leading to collapse.

Is it possible for any composite particle (Neutron) to loss its hydrostatic equilibrium without losing its mass?

It the article it is stated:
https://www.forbes.com/sites/starts...collapse-to-form-black-holes/?sh=414c81c37159

"The Pauli exclusion principle, which only applies to fermions, not bosons, states, explicitly, that in any quantum system, no two fermions can occupy the same quantum state. It means that if you take, say, an electron and put it in a particular location, it will have a set of properties in that state: energy levels, angular momentum, etc.
If you take a second electron and add it to your system, however, in the same location, it is forbidden from having those same quantum numbers. It must either occupy a different energy level, have a different spin (+1/2 if the first was -1/2, for example), or occupy a different location in space."
Protons and neutrons are similar. Despite being composite particles, made up of three quarks apiece, they behave as single, individual fermions themselves. They, too, obey the Pauli Exclusion Principle, and no two protons or neutrons can occupy the same quantum state.

Based on the above law of physics it is impossible for two neutrons to occupy the same quantum state/same space.
Therefore, why can't we claim that if we break the Neutrons, we also break their properties?
One of the key property of the neutron is its mass.
Therefore, how billions over billions of neutrons could keep their properties/mass while they all collapse into a Black hole and occupy the same quantum state/same space?

 

[Drakkith]

Based on the above law of physics it is impossible for two neutrons to occupy the same quantum state/same space.
Therefore, why can't we claim that if we break the Neutrons, we also break their properties?
One of the key property of the neutron is its mass.
Therefore, how billions over billions of neutrons could keep their properties/mass while they all collapse into a Black hole and occupy the same quantum state/same space?

They can't.* That's one of the things we don't know about black holes. We don't know what happens to matter that falls inside. It's unlikely that it simply disappears, as that would violate various conservation laws. Our best explanation is that the black hole evaporates slowly over time via hawking radiation but what exactly happens to matter that falls into the black hole is unknown at this time.

*Note that mass is conserved, even when particles change into other particles. The mass of the protons and electrons that combine during supernovas to form the neutrons that make up the neutron star is not lost. It goes into forming the neutrons. The same thing would happen if neutrons are forced to change into something else. Their mass would go into that new system.

 

[davLev]

Therefore, how billions over billions of neutrons could keep their properties/mass while they all collapse into a Black hole and occupy the same quantum state/same space?

They can't.* That's one of the things we don't know about black holes. We don't know what happens to matter that falls inside. It's unlikely that it simply disappears, as that would violate various conservation laws.

Thanks

Do appreciate your reply.

As the matter can't occupy the same quantum state/same space without breaking the law of science, then why do we insist for a singularity in a BH?

Why can't we agree that even BH should have some sort of internal space/radius?

Our best explanation is that the black hole evaporates slowly over time via hawking radiation but what exactly happens to matter that falls into the black hole is unknown at this time.

What about SMBH and quasars?
Do we believe that all of them evaporate slowly over time via hawking radiation?

*Note that mass is conserved, even when particles change into other particles. The mass of the protons and electrons that combine during supernovas to form the neutrons that make up the neutron star is not lost. It goes into forming the neutrons. The same thing would happen if neutrons are forced to change into something else. Their mass would go into that new system.

Neutron is a composite particle (3 quarks and gluons)

All the 3 quarks contribute only 1% to its mass, while the gluons contribute 99%.
As long as we keep the gluons inside the neutron / proton, then we also keep its total mass.

However, what could be the outcome of collapsing this composite particle?
We have an evidence that the "average peak pressure, near the center of the proton, comes out to 10^35 pascals"
However, do we know what is the "average peak pressure, near the center of the quark?
Could it be that the average peak pressure of the quarks is higher than this value of 10^35?

If so, why can't we assume that if the pressure crosses the 10^35 pascals (but not high enough to break the quarks) then the neutron would be broken to its composite particle - quarks and gluons.
Could it be that the gluons mass would be lost once it is outside the neutron but the quark mass would be kept?

In that article it is stated:
The Surprising Reason Why Neutron Stars Don't All Collapse To Form Black Holes
They also specifically discuss about quark star.
"a neutron star or even a strange quark star are all still made of fermions."

If we add the impact of the spinning motion on the total gravity, could it be that Black hole is actually massive neutron (or quark) star which must have some sort of minimal radius?

 

[PeterDonis]

This textbook was published in 1983.

Yes.

For me, evidence means observation.
I wonder what kind of observation Shapiro & Teukolsky have used to justify their theoretical astrophysics of Compact Objects?

Read the book and see. If you are under the impression that there was no such evidence in 1983, you are egregiously mistaken.

If the rotation of the neutron star is almost at the speed of light, could it decrease dramatically the total gravity?

If you would go and read Shapiro & Teukolsky, you would see that they discuss exactly this case. The answer is no, it won't decrease "dramatically" gravity, and it won't increase "dramatically" the maximum mass. Nothing that has been discovered since has changed that.

 

[PeterDonis]

Based on the above law of physics it is impossible for two neutrons to occupy the same quantum state/same space.
Therefore, why can't we claim that if we break the Neutrons, we also break their properties?

If you "break" neutrons, you get quarks. Which are still fermions.

As the matter can't occupy the same quantum state/same space without breaking the law of science, then why do we insist for a singularity in a BH?

Nobody "insists" on a singularity inside a BH. In fact, most physicists believe that the fact that GR predicts a singularity inside a BH means that GR is an incomplete theory, and is expected to be replaced by a more fundamental theory, probably some form of quantum gravity, in the regime where spacetime curvature reaches the Planck scale.

However, that regime is still far inside a black hole, and has nothing to do with the event horizon and the physics in that regime. Nor does it have anything to do with the maximum mass limits on white dwarfs and neutron stars. In other words, it in no way changes the prediction of formation of black holes by gravitational collapse. It only changes what might be deep inside black holes once they are formed.

Why can't we agree that even BH should have some sort of internal space/radius?

A BH is not a point. It does have spacetime inside it. You do not appear to have a good grasp of what our models of black holes actually say.

What about SMBH and quasars?
Do we believe that all of them evaporate slowly over time via hawking radiation?

That is the current belief, yes. However, we have no evidence of such evaporation, nor do we expect to get any any time soon. Indeed, even without any other matter or radiation falling into a black hole, the CMBR temperature is higher than the Hawking temperature of all the black holes we have observed, so those holes right now, and for a very, very long time in the future, will not be evaporating, they will be very slowly gaining mass as CMBR radiation falls into them.

 

[PeterDonis]

he neutron would be broken to its composite particle - quarks and gluons.
Could it be that the gluons mass would be lost once it is outside the neutron but the quark mass would be kept?

No. You evidently do not have a good understanding of the process you are talking about, or of gluons and quarks in general.

Gluons are massless; they have zero rest mass, just like photons. Their energy is entirely kinetic energy; how much of it they have depends on how small a volume they are confined to.

The "neutron breaking" you describe happens under extreme pressure, which means the quark-gluon plasma you get under these extreme conditions, when there is no longer any meaningful neutron structure, is confined to a very small space--the quarks and gluons that made up a neutron are actually confined to a smaller volume than they were when they made up a neutron. They don't go anywhere and they don't lose any energy; indeed, their energy per particle is higher than when they made up a neutron, because they are confined to a smaller space.

If we add the impact of the spinning motion on the total gravity, could it be that Black hole is actually massive neutron (or quark) star which must have some sort of minimal radius?

No. None of the references you give say any such thing.

Also, all the references you give are pop science articles. They are not good sources for learning actual science. You need to be looking at textbooks and peer-reviewed papers. All you are doing at this point is misinterpreting pop science articles that already aren't good descriptions of the actual science, and then asking uninformed questions. That is not a good way to learn science.

 

[davLev]

In fact, most physicists believe that the fact that GR predicts a singularity inside a BH means that GR is an incomplete theory, and is expected to be replaced by a more fundamental theory, probably some form of quantum gravity, in the regime where spacetime curvature reaches the Planck scale.

Wow!

Nobody "insists" on a singularity inside a BH.

A BH is not a point. It does have spacetime inside it.

Thanks
As you confirm that BH is not a singularity or a point and It does have spacetime inside it, then do you agree that BH must have some minimal space/volume/radius?

 

[PeterDonis]

As you confirm that BH is not a singularity or a point and It does have spacetime inside it, then do you agree that BH must have some minimal space/volume/radius?

No. It has spacetime inside it, but there is no "minimal" amount that it must have.

 

[Drakkith]

As you confirm that BH is not a singularity or a point and It does have spacetime inside it, then do you agree that BH must have some sort of space/volume/radius?

That's... complicated. Per this article: https://arxiv.org/abs/0801.1734

The area of a Schwarzschild black hole is unique, and can be defined by an idealized transverse measurement of a particular spherical surface. In contrast, the volume inside a black hole requires a definition of the particular 3-space in which the volume is computed, which may be explicitly time dependent, and an understanding of the (possibly time dependent) limits of the integral required to compute this volume.

 

[davLev]

No. It has spacetime inside it, but there is no "minimal" amount that it must have.

If it has spacetime, then how could it be that it has no space or volume?
Can you please explain the contradiction?

Please be aware that the number of atoms in the sun comes to 1.201×10^57.
Therefore, in a neutron star with one solar mass there should be at least 10^57 neutrons while a BH with one solar mass should have 10^57 neutrons mass.
SMBH could have 10^6 solar mass = 10^63 Neutrons/protons mass
Quasar could have 10^9 solar mass = 10^66 Neutrons/protons mass.

Therefore, why can't we agree that SMBH with 10^6 solar mass should have bigger volume than a BH with one solar mass (by about 10^6), while quasar should have a bigger volume than SMBH (by about 10^3)?

If you still disagree, then how can we fit the whole quasar mass (10^9 solar mass) in the same volume of a BH with a single solar mass?

 

[Ibix]

If it has spacetime, then how could it be that it has no space or volume?

The volume of a black hole is not well defined. You can get different answers depending on how you choose to assess it. Having infinite interior volume is a perfectly reasonable answer, or it can vary with time.

You can define the surface area of the event horizon. You can derive a so-called "areal radius" from this using $A=4\pi r^2$, but because the interior of the black hole is not Euclidean this is not "the distance to the center" (and "distance to the center" is an elusive concept inside the hole). Optically, from a distance it appears to be somewhat more than 1.5 times that radius due to the curvature of light rays.

The key point to realise is that what we call "the black hole" is the region inside the event horizon. There's no need for that region to be filled with matter. And the other key point to realise is that we do not know of any mechanism to stop the collapse of matter. Fermion degeneracy pressure (what you were talking about with two particles not wanting to occupy the same state) supports neutron stars. Once the pressure is too high for that to stop collapse we know of nothing else that can.

The result of allowing collapse to continue unchecked is the black hole singularity. Nobody thinks this is particularly plausible, but it's most likely a problem with general relativity - hence the search for a quantum theory of gravity. Simply saying (as you seem to be doing) "something must stop the collapse" is overly simplistic - we know we don't understand any of the rules right at the heart of a black hole.

Dragging this back to the original topic, we're pretty confident that we understand how big a black hole appears on camera, and it is fairly simply related to the mass and spin and independent of exactly what happens inside. Neutron stars are far more complicated because their size does depend on the details of what goes on inside. And those details are relatively poorly understood, so observational bounds on how they actually behave is useful in refining our models.

 

[PeterDonis]

If it has spacetime, then how could it be that it has no space or volume?

I didn't say it has no space or volume. Go read what I said again.

Can you please explain the contradiction?

There is no contradiction. You are just not reading very carefully.

 

[PeterDonis]

why can't we agree that SMBH with 10^6 solar mass should have bigger volume than a BH with one solar mass (by about 10^6), while quasar should have a bigger volume than SMBH (by about 10^3)?

Because of the issue described in the paper @Drakkith linked to. Which boils down to what @Ibix said:

The volume of a black hole is not well defined.

 

[davLev]

The volume of a black hole is not well defined.

Thanks for your comprehensive reply.

Please be aware that I didn't ask what is the volume, I have asked if BH has a volume.
If the Black hole is not well defined, then we have to agree that it could have a volume.
If we claim that a black hole has no volume, then by definition we defined the volume.

I didn't say it has no space or volume. Go read what I said again.

As you have confirmed that a BH is not a point. It does have spacetime inside it, while you didn't say that BH has no space or volume, then can we at least agree that it could have a volume?

Fermion degeneracy pressure (what you were talking about with two particles not wanting to occupy the same state) supports neutron stars. Once the pressure is too high for that to stop collapse we know of nothing else that can

If we wish to obey law of science then the understanding that "two particles not wanting to occupy the same state" should be valid to any kind of object including Neutron stars and BHs.

The result of allowing collapse to continue unchecked is the black hole singularity. Nobody thinks this is particularly plausible, but it's most likely a problem with general relativity - hence the search for a quantum theory of gravity. Simply saying (as you seem to be doing) "something must stop the collapse" is overly simplistic - we know we don't understand any of the rules right at the heart of a black hole.

Did we ever observe a Neutron star as it collapse into BH?
As there might be a problem with general relativity, and as we know we don't understand any of the rules right at the heart of a black hole, then could it be that there is an error with the assumption of singularity in a BH?

Neutron stars are far more complicated because their size does depend on the details of what goes on inside.

A question with regards to Neutron star:
The event horizon radius for any one solar mass object is fully defined = 3Km.
https://www.astro.ucla.edu/~ghezgroup/gc_edit/Latest/faq.html
The event horizon is 3km (a little less than two miles) for our Sun, or any one-solar-mass object. For more massive black holes, the size of the event horizon scales linearly; ten-solar-mass black hole would have a 30-km event horizon.

That definition works for a BH and Neutron star (with one solar mass).
The radius of the neutron star is also fully defined = 10Km.
https://www.toppr.com/ask/question/...and-a-neutron-stareach-of-one-solar-mass-the/
The radius of the neutron star with one solar mass is 10 km.

As we have full definition for the radius of Neutron star (10Km) and its event horizon (3Km), then would you kindly explain why we can't see its surface which should be located outside the event horizon?

As we can't see the surface of a Neutron star although its radius is bigger than the event Horizon, then could it be that we have an error in our definition about Neutron star?

 

[PeterDonis]

Please be aware that I didn't ask what is the volume, I have asked if BH has a volume.

The answer is that the volume of a black hole is not well-defined.

If the Black hole is not well defined

Nobody said a "black hole" is not well-defined. It is. What is not well-defined is the volume of a black hole.

then we have to agree that it could have a volume.

"Not well-defined" doesn't mean "might have a volume or might not". It means that, given a particular black hole, there is no one unique number that is the "volume" of the hole. You can get pretty much any number greater than zero and less than infinity, depending on how you define "volume". There is no one unique answer.

If we claim that a black hole has no volume

Nobody has claimed that. Again, you need to read more carefully. You keep responding to things that nobody has said, and you do not appear to be properly comprehending what people have said.

If we wish to obey law of science then the understanding that "two particles not wanting to occupy the same state" should be valid to any kind of object including Neutron stars and BHs.

BHs are not made of fermions, so no, this is not valid for BHs. It is valid for matter made of fermions that collapses to a black hole, but the black hole itself is not the same thing as the matter that collapsed to form it.

Did we ever observe a Neutron star as it collapse into BH?

Not directly, no. But there is plenty of indirect evidence to support our best current models of such a process.

As there might be a problem with general relativity

There is no such problem with regard to the process of a neutron star (or any other object) collapsing to a black hole.

as we know we don't understand any of the rules right at the heart of a black hole,

That's not correct. We do have a set of rules; that set of rules predicts that the matter that collapses to form a black hole collapses to zero size and is destroyed in a singularity.

Many physicists hypothesize that this prediction of GR means that GR is an incomplete theory, and that at very large spacetime curvatures, encountered just before GR predicts that there is a singularity, GR breaks down and some other theory, presumably some form of quantum gravity, takes over. But this is a hypothesis. It's not a proven fact and there is no evidence which requires us to consider it. It's just a theoretical issue that many physicists believe will have to be resolved at some point. That's all it is.

could it be that there is an error with the assumption of singularity in a BH?

See above.

That definition works for a BH

Yes.

and Neutron star (with one solar mass).

No. A neutron star (or any other object that is not a black hole) has no event horizon, and the "Schwarzschild radius" calculation is physically meaningless for such an object.

would you kindly explain why we can't see its surface which should be located outside the event horizon?

Nobody has claimed that we cannot see the surface of a neutron star. You can't see the surface of a black hole.

 

[PeterDonis]

@davLev at this point I am closing this thread. You keep "responding" to claims that nobody has made; you are not reading what people have said carefully; and you keep referencing pop science sources instead of going and looking at textbooks or peer-reviewed papers to learn the actual science. At this point the actual substantive questions you have asked have been thoroughly responded to.

I strongly suggest that you take some time to learn the relevant science from valid sources before posting about this subject again.

Thread closed.