Science Questions

Is it possible there is a new element hidden inside a Neutron star?

Mon, 3rd Oct 2016

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Paul asked:

Is it possible there is a new element hidden inside a Neutron star,as the laws of gravity dictate that the bigger the object the more gravity it has using all the known elements? However, a Neutron star has a gravity a million times more than Earth and is no more than twenty miles across. I realize conventional theory says Neutron stars are extremely compact because the space inside an atom is mostly made from space an it is that what is compressed. But under that sort of compression you would get an explosion like that of a supernova (the thing that caused it). Do you think it is a least theoretically possible?


You reason you do not see this element throughout the universe could be that it has such a strong magnetic pull it it not scattered throughout the universe but only found sticking together in a Neutron stars. When you think about it, tremendous heat is required to form new elements i.e Supernova. Bingo that's what forms Neutron stars!


We put Paul's question to Judith Croston... Artist's illustration of an 'isolated neutron star'

Judith - Okay, so to the answer to this is no, but it’s quite interesting why. So I should start perhaps by briefly explaining what a neutron star is. So, just as a reminder, a neutron star is one of these really strange stars. You take an ordinary star, so you could say take all of the matter in our solar system and squash it down to an incredibly high density so you could fit our solar system inside the M25, basically. Neutron stars are about ten kilometers in size but they all the matter inside them that an entire solar system could have.

Chris - Like one teaspoon full weighs millions of tons?

Judith - Yes. A teaspoon full could weigh the same as Mount Everest or something so they’re very strange. The physics of them is really weird. They have very strong gravity but the important thing is the density and the pressure in the centre of neutron star is so incredibly high we just don’t understand how physics work in those conditions, we can’t do experiments in the lab.

So there are quite a lot of exotic theories about what could happen in the centre of a neutron star, but one thing that couldn’t happen is the creation of a new chemical element similar to the sorts of things we have on the periodic table because chemical elements have protons and neutrons bound together and then they have orbits of electrons spinning around. And what happens in a neutron star is that as, when the star forms the protons and the electrons that were there, and the nuclei from the star, they combine together so the electrons and the protons combine together to make neutrons. So there’s no space to have these orbitals of electrons spinning around so you couldn’t make a new element like that.

On the other hand, there are theories about all sorts of weird things that could go on in the centre of neutron stars because the neutrons themselves might break down into quarks, which are the little particles that you get inside neutrons and protons. And then those quarks can do quite strange things and then combine together in various ways. So people are quite interested in trying to figure out the physics of neutron stars because it might tell us something interesting about those sorts of exotic states.


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The nucleus of an atoms has the protons and neutrons so close they are effectively touching.
In a neutrons star, all the neutrons, and any residual protons present are almost close enough to touch (it is the residual electrons that stop it from collapsing further, into a black hole).
So in one sense, the bulk of a neutron star could almost be considered as one massive nucleus, with a ridiculously high atomic mass.

Magnetic fields from an atom can be produced by unpaired electrons, or unpaired nucleons (protons or neutrons).
A single atom does not usually produce an enormously large magnetic field from all the electrons being aligned, because:
- In a neutron star (or an ordinary star), many of the electrons are stripped off the atom.
- The Pauli exclusion principle ensures that electrons can't have the same spin in the same orbit
-  it becomes energetically favorable for electrons to flip their spin (canceling the magnetic field), and move into a lower energy state
- Similar logic applies to the spins of nucleons - in a sense, nucleons often form in stable subgroups inside the nucleus with two protons and two neutrons with zero net spin; we often see these groups spat out from radioactive elements as an alpha particle.

It is thought that when a neutron star forms, the magnetic field of the star is compressed into an extremely small volume, and "frozen in" (but at an extremely high temperature). This can produce enormously strong magnetic fields at the surface.

See: evan_au, Wed, 17th Aug 2016

No. It's not possible. There are no atoms at all inside a neutron star, only neutrons. Any atom (i.e. element) that gets absorbed by a neutron star becomes part of the neutron star as its electrons and protons combine into neutrons and those neutrons become part of the neutron start. As Evan explained, a neutron star is just a massive nucleus consisting of neutrons only. No atom can exist inside a neutron star.

Its unclear to me where you got that notion from. A neutron star cannot go supernova. The compression of the star doesn't mean that you'd get such an explosion. The strong force is much greater than the gravitational force and both forces hold a neutron star together.

Absolutely not. PmbPhy, Thu, 18th Aug 2016

That is not in agreement with in which the existence of identifiable atomic nuclei is indicated as an expected phenomenon.  The extreme pressure, it appears, permits the continuance of species that on Earth would quickly decay, suggesting that elements heavier than those yet identified on Earth may occur. Atomic-S, Thu, 18th Aug 2016

The force that would allow such elements to form would be gravitational, not magnetic. Atomic-S, Thu, 18th Aug 2016

That is not in agreement with in which the existence of identifiable atomic nuclei is indicated as an expected phenomenon.  The extreme pressure, it appears, permits the continuance of species that on Earth would quickly decay, suggesting that elements heavier than those yet identified on Earth may occur.

To be precise, you're correct. But that's on the surface of the neutron star and I was referring to matter "inside a neutron star." PmbPhy, Thu, 18th Aug 2016

Why is a neutron star made only of neutrons, and how did that happen? chris, Thu, 18th Aug 2016

Neutron stars are formed in supernova explosions.
- The immense pressures of the gravitational collapse of a star forces protons and electrons together, forming neutrons, and emitting neutrinos.
- The neutrinos deposit enough energy in the dense infalling matter to blow away the outer layers of the star, which produces the flash we see as a supernova.

There are still a few electrons and protons (and heavier nuclei) floating around in a neutron star, especially in the outer layers where the pressures are lower (but still astronomical!).


...And now we have neutrino telescopes, we should be able to detect future supernovas in our galaxy (provided the star doesn't collapse directly to a black hole before the neutrinos are emitted - a "dark supernova"). evan_au, Thu, 18th Aug 2016

Thank you; so why is the gravitational collapse more powerful than the gravity of the host star to start with? Is it the unopposed collapse that is occurring secondary to the fall-in of the core that means that the particles develop significant momentum as they accelerate inwards? chris, Fri, 19th Aug 2016

There are many types of supernova; the ones that form neutron stars and black holes are called "core collapse" supernovas, where the center of the star can no longer hold back the immense pressure of the overlying gas, and the whole star collapses inwards at enormous velocity.

There are a number of forces at the center of a star that can hold back the gravitational attraction of the star - the simplest being pressure caused by the high temperatures at the center of the star.
- to hold back the weight of a large star, the core must remain very hot.
- When a large star has burnt all the hydrogen in its core to iron, it can no longer generate heat by fusion (iron being the most stable element)
- The core starts to cool down, and the star shrinks
- the force of gravitational attraction increases (because the star's mass is now much closer together)
- Under sufficient pressure, iron fusion begins - but rather than releasing energy, it absorbs energy
- This cools the core, causing it to collapse even faster
- This runaway collapse can halt when the protons and electrons are crushed into neutrons (releasing neutrinos) - or it may proceed all the way to a black hole. 

For some other scenarios, see: evan_au, Fri, 19th Aug 2016

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