[Aeris (OP)]

Neutron Stars may very well be the single coolest things I've ever heard of in the expansive world of Cosmology. I mean, an unfathomably dense celestial body birthed from the death of a supermassive star made entirely out of electrically-neutral particles? How cool sounding is that?! Neutron Stars are awesome!

With that in mind however...

They're also some of the most confusing and brain-scratching things I've ever heard of in the Universe (and trust me, I've heard of A LOT of things), and since this is a website made entirely for the sole purpose of educating people about strange things they don't fully understand, I was hoping to finally cure my confusion about these spherical little buggers.

Question 1. Are Neutron Stars really made up of ONLY Neutrons and absolutely nothing else whatsoever, or is this a scientific misconception?
Question 2. Assuming Neutron Stars really are made up of only Neutrons, what exactly holds them together and keeps them stable? I mean, it can't be the Electromagnetic force if it's made up of only Neutrons, right?
Question 3. The reason why we're not able to see Dark Matter with our eyes or our various forms of technology is because it doesn't interact with the Electromagnetic force and therefore doesn't emit, reflect or even absorb light. If Neutron Stars had a similar thing going on, it would be logical to assume that they too don't interact with light in any way shape or form and would therefore be invisible as well. Despite this however, we can quite clearly see Neutron Stars with our eyes, and in color no less. How is this possible?
Question 4. What would a Neutron Star feel like to touch? Obviously we would have to ignore the existence of the insane thermal radiation, blinding light, super strong gravitational field and super strong magnetic field, but would the star itself feel like normal, gaseous plasma stars, or something else entirely? If it really is made up of only Neutrons, would you just fall right through it due to the lack of the Electromagnetic force simulating the sensation of touch (this is after all, the force that allows things to touch each other in the first place).
Questions 5. How feasible on a scale of 1 to 10 would it be to engineer everyday objects and materials out of the same stuff Neutron Stars are made of? Would use could these things possibly have if we could feasibly make them?
Question 6. If a Strangelet came into contact with some ordinary matter and converted it into strange matter, would it be impossible to convert it back into what it once was? Where do Strangelets even get the energy needed to do this anyway?
Question 7. Are Strangelets the best candidates for the true identity of the illusive Dark Matter?       

[Kryptid]

Neutron stars are mostly neutrons, but not entirely. There are still some protons and electrons left in there, mostly near the surface where there is less pressure.

Conservation laws aren't violated when protons combine with electrons to create neutrons because a neutrino is also created in the process.

Neutron stars are held together by immense gravity.

[Aeris (OP)]

"Neutron stars are mostly neutrons, but not entirely. There are still some protons and electrons left in there, mostly near the surface where there is less pressure."

So... there are Protons and Electrons surrounding the star, but the actual star itself is still made up of mostly Neutrons?

"Conservation laws aren't violated when protons combine with electrons to create neutrons because a neutrino is also created in the process."

I just looked up what kind of particles Neutrons and Neutrinos are and funnily enough they're considered Baryons and Leptons respectively. I never knew that.

[Halc]

Question 2. Assuming Neutron Stars really are made up of only Neutrons, what exactly holds them together and keeps them stable? I mean, it can't be the Electromagnetic force if it's made up of only Neutrons, right?

Gravity holds them together. They're stable because there's nothing else they can be. It would require energy to say decay them into a proton/electron since there's no room for that pair. So it's stable.

It's not just a solid ball of neutrons. The inner crust is made of essentially superfluid neutrons. The outer crust has ions and electrons. The outer core has protons of all things, implying a massive charge imbalance between the inside and outside.  See wiki page showing pictures of the how the more current models lay it out.

Question 3. The reason why we're not able to see Dark Matter with our eyes or our various forms of technology is because it doesn't interact with the Electromagnetic force and therefore doesn't emit, reflect or even absorb light. If Neutron Stars had a similar thing going on, it would be logical to assume that they too don't interact with light in any way shape or form and would therefore be invisible as well.[/quote]Of course they interact with the various forces. Something needs to keep it from collapsing, which is mostly the strong force. Dark matter doesn't interact with the strong force, and would pass right through a neutron star and out the other side. Light does not do this, so a neutron star doesn't behave at all like dark matter. They emit/reflect light just fine, so you can see them.

Question 4. According to a YouTube video I found online, Neutron Stars form when the pressure of a collapsing star gets so great, that Protons and Electrons fuse together into Neutrons. Assuming this information is correct, how the hell does this not violate conservation of Baryon and Lepton number?

This goes on all the time in our sun, creating neutrons at the rate of tons per second, and no violation occurs. It does involve creation of a neutrino which probably exits the star. See proton-proton reaction.

Question 5. What would a Neutron Star feel like to touch? Obviously we would have to ignore the existence of the insane thermal radiation, blinding light, super strong gravitational field and super strong magnetic field

That eliminates pretty much all of what it would be like. It's just a hard rock with all that taken away, despite it being liquid on the surface.

but would the star itself feel like normal, gaseous plasma stars, or something else entirely?

There is an atmosphere if that's what you're asking. The hard part is below that. Our sun is pretty much all plasma

If it really is made up of only Neutrons, would you just fall right through it

Of course not. The other forces would prevent you from penetrating, else it would fall into itself.

the lack of the Electromagnetic force simulating the sensation of touch (this is after all, the force that allows things to touch each other in the first place).

That's because EM stops you before your atoms get close enough to the door knob to allow other forces to come into play.

Questions 6. How feasible on a scale of 1 to 10 would it be to engineer everyday objects and materials out of the same stuff Neutron Stars are made of?

Would think not at all. It isn't stable without the pressure, and there's no EM way to generate that sort of pressure.

No idea about strangelets.

[Aeris (OP)]

"Gravity holds them together. They're stable because there's nothing else they can be. It would require energy to say decay them into a proton/electron since there's no room for that pair. So it's stable."

"It's not just a solid ball of neutrons. The inner crust is made of essentially superfluid neutrons. The outer crust has ions and electrons. The outer core has protons of all things, implying a massive charge imbalance between the inside and outside.  See wiki page showing pictures of the how the more current models lay it out."

Oh. So... it's NOT made only out of Neutrons? That's... honestly really lame, ngl.

"Of course they interact with the various forces. Something needs to keep it from collapsing, which is mostly the strong force. Dark matter doesn't interact with the strong force, and would pass right through a neutron star and out the other side. Light does not do this, so a neutron star doesn't behave at all like dark matter. They emit/reflect light just fine, so you can see them."

Does Dark Matter even react with ANY of the four forces?

"This goes on all the time in our sun, creating neutrons at the rate of tons per second, and no violation occurs. It does involve creation of a neutrino which probably exits the star. See proton-proton reaction."

I've been led to believe that all of the Sun's energy came from the nuclear fusion processes happening in its core where Hydrogen atoms are fused together into Helium. Not too long ago I was told that the Sun also produced Antimatter. Now I'm just learning that they also produces neutrons AND neutrinos?! Is there anything ELSE that the Sun does that I don't know about?

"That eliminates pretty much all of what it would be like. It's just a hard rock with all that taken away, despite it being liquid on the surface."

I didn't mean ignore as in get rid of. I meant ignore as in you, the person touching it, weren't affected by the things whatsoever (basically Superman). Yeah, that's not realistic in the slightest, but I'm sure you can imagine such a scenario so long as it helped make the question easier to answer.

"Would think not at all. It isn't stable without the pressure, and there's no EM way to generate that sort of pressure."

Engineer was the wrong word. I meant extracting pieces of a Neutron Star with a giant megastructure of sorts and then building materials and objects from that. Would that be slightly more plausible?

[evan_au]

Question 1. Are Neutron Stars really made up of ONLY Neutrons

As mentioned above, there is a thin outer shell of plasma (iron nuclei and electrons), at extremely high temperature (eg 600,000C).
What is in the middle is less clear - we can't easily bang neutrons together at high velocity and see what happens.
Some people think that at extreme pressures, there may be a further phase change, and the individual neutrons might break down into a denser "quark soup" - a so-called quark star.

The NICER experiment on the ISS is trying to confirm this theory (or not) by measuring the radius and mass of neutron stars; from this they can see if the density exceeds the maximum packing density of neutrons, implying that quark stars might exist.
 See: https://en.wikipedia.org/wiki/Neutron_Star_Interior_Composition_Explorer

Question 3: would be logical to assume that (neutron stars) too don't interact with light .. and would therefore be invisible as well

The extreme temperature of the outer shell of a neutron star produces "black body radiation" extending well into the X-Ray region of the spectrum, and down into the infra-red (the intense radio pulses of certain neutron stars "pulsars" possibly come from other mechanisms to do with the intense magnetic field).
"Hot Spots" on the surface act as a lighthouse, spinning around so we see them flashing in our direction.

Question 5. What would a Neutron Star feel like to touch?

You can't touch it.
The intense gravitational field would rip your fingertips off your fingers, rip your fingers off your hands, and rip your arms off your body (spaghettified).
And all this before you came even close to the neutron star.

extracting pieces of a Neutron Star with a giant megastructure

You are describing mining a neutron star.

Let's think of the reverse - how a neutron star is formed.
Something 1 to 1.5 times mass of the Sun (say 1 million km across) compresses down into a neutron star perhaps 20km in diameter, 50,000 times less.
As soon as you extract a piece of neutron star, it would be relieved of the intense gravity holding it together, and all the neutrons would rapidly decay (about half every 12 minutes), forming a hot, intensely radioactive plasma that takes up 10¹⁴ times more volume - the ultimate neutron bomb.

This is added to the problems of the spaghettification of your equipment, the fact that it would be crushed into a mere smear on the surface (even mountains are thought to be less than 1mm high) and the fact that no solid matter can exist at the 600,000C surface temperature of a neutron star.

brain-scratching

If you want to read a science fiction novel that weaves an alien plot around the known (or inferred) physics of the surface of neutron stars, Read "Dragon's Egg" by Robert Forward.
https://en.wikipedia.org/wiki/Dragon%27s_Egg 

[Halc]

Oh. So... it's NOT made only out of Neutrons? That's... honestly really lame, ngl.

Apparently the protons (or more accurately, positively charged 'quark soup' as evan points out) and electrons can't get to each other, preventing further reactions that would make more neutrons. Still, how do the protons end up in the middle instead of mixed through the neutrons like they are in a large nucleus? Under such conditions, they are perhaps more dense, allowing more mass to pack into less space, and hence the neutrons buoy up forming the 'insulating' layer outside. I can't say for sure.

Does Dark Matter even react with ANY of the four forces?

Just gravity, and if you don't count that as a 'force', then there's only three forces and dark matter doesn't interact via any of them. But dark matter still causes gravitational time dilation if you concentrate it somewhere, so that's a gravitational effect.
Dark matter shoots straight through a neutron star and back out, but if it comes within the photon-sphere of a black hole, it's not ever coming out, and it adds to the mass of the black hole.

I've been led to believe that all of the Sun's energy came from the nuclear fusion processes happening in its core where Hydrogen atoms are fused together into Helium.

That's a very short description, but hydrogen is made of just a proton, and the neutrons need to come from somewhere, so the process has to involve the creation of them if it is to make helium, which is two of each. That's why our attempts to fuse hydrogen on Earth first has to find the rare isotope of hydrogen ²H with the neutron already present. ¹H (a lone proton) just doesn't fuse to anything.

Not too long ago I was told that the Sun also produced Antimatter.

Yes, as part of the neutron-creation process. Two protons collide and one emits a neutrino and a positron, leaving a neutron behind. Charge/lepton-number is nicely preserved. Everybody goes home happy.

Is there anything ELSE that the Sun does that I don't know about?

We all could spend a lifetime and still not know all about the sun, or about any other subject for that matter.

I didn't mean ignore as in get rid of. I meant ignore as in you, the person touching it, weren't affected by the things whatsoever (basically Superman).

Hard to say. What are you touching? The outermost layers? That's like touching Earth by colliding with one upper-most atmosphere atom. You'd not notice.
With a neutron star, it would be fatal to a human to even get close to it, like in low orbit or something. So you'd need to be superman just to be there, let alone actually contact anything.

So I said it was 'hard'. You'd not be able to move the surface, except to make waves of some sort in the atmosphere.

Engineer was the wrong word. I meant extracting pieces of a Neutron Star with a giant megastructure of sorts and then building materials and objects from that. Would that be slightly more plausible?

You'd have to use something like EM force to do it, and it obviously is being dwarfed by the other forces, so no way to touch it with any tool without the tool just becoming part of it.
If you had a piece of it, it wouldn't be stable for even an instant, and would probably act like a bomb or something. It needs the pressure to be stable.

[Kryptid]

I didn't mean ignore as in get rid of. I meant ignore as in you, the person touching it, weren't affected by the things whatsoever (basically Superman). Yeah, that's not realistic in the slightest, but I'm sure you can imagine such a scenario so long as it helped make the question easier to answer.

If you were Superman, you could indeed touch a neutron star's surface and it would be hard and extremely smooth. The reason is that neutrons and protons obey the Pauli exclusion principle: the neutrons and protons in the atoms of your hand would be stopped by the neutrons and protons that make up the star's solid crust because the available energy levels are filled (it's degenerate matter). There'd be nowhere for your nuclei to go. I presume you actually could move around inside of the neutron's star superfluid layer because, of course, it's a fluid.