B The star's core cannot withstand its own gravitational force?

[Karagoz]

As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force.The core collapses, which results in the giant explosion of a supernova.
Source: https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-supernova.html

What does it mean that the core cannot withstand its own gravitational force?

How and why the core cannot withstand its own gravitational force and then explode?

 

[phinds]

What does it mean that the core cannot withstand its own gravitational force?

The gravity at the outer edge of a star is TREMENDOUS. The only reason it does not compress much further is that the gravity is balanced by the force of the particles streaming out from the core because of fusion. When the fusion runs out, gravity wins and the outer parts fall inward and the explosion happens. You should be able to find LOTS of descriptions of this online.

 

[Drakkith]

What does it mean that the core cannot withstand its own gravitational force?

How and why the core cannot withstand its own gravitational force and then explode?

Just before a core-collapse supernova, the pressure on the core is so high that it becomes energetically favorable for electrons and protons to combine into neutrons (a process which requires energy). This pressure comes from the weight of the outer layers of the star pressing down on the core, which, in a star massive enough undergo a supernova, is truly immense. As the electrons and protons combine, the repulsive force from all of those electrons is removed and the star's core collapses in on itself. This lasts until the density is so high that neutron degeneracy pressure stops the collapse, turning the star into a neutron star, or, if the mass in the core is high enough, the star progresses straight to a black hole.

If the star progresses to a neutron star, this collapse is halted when neutron degeneracy pressure becomes dominant and halts the collapse. This sudden halt causes the material in the outer layers, which is now rapidly accelerating inwards towards the vacant area where most of the core used to be, to rebound off of the surface of the newly formed neutron star. This rebound (along with one or more currently unknown mechanisms) is what blasts the outer layers outwards away from the star in a supernova explosion.

See the following articles:
https://en.wikipedia.org/wiki/Supernova#Core_collapse
https://en.wikipedia.org/wiki/Neutron_star#Formation

 

[Karagoz]

So it first collapses, and then the "explosion" happens after the collapse?

The "explosion" is caused by the halting of the collapse because of neutron degeneracy pressure, which then causes rebound of the outer matter in outer layers?

Does the broken strong nuclear forces on quark level play a role in the explosion of the core?

 

[davenn]

So it first collapses, and then the "explosion" happens after the collapse?

yes

The "explosion" is caused by the halting of the collapse because of neutron degeneracy pressure, which then causes rebound of the outer matter in outer layers?

did you read Drakkith's post and have a look at the links he provided ?

 

[Drakkith]

Does the broken strong nuclear forces on quark level play a role in the explosion of the core?

I'm sorry but I don't quite understand what you're asking. What do you mean by the "broken" strong force?

 

[stefan r]

As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force.The core collapses, which results in the giant explosion of a supernova.
Source: https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-supernova.html

What does it mean that the core cannot withstand its own gravitational force?

How and why the core cannot withstand its own gravitational force and then explode?

Any object on Earth's surface held up by electrons. The atoms in you bum cannot pass into your chair because the electrons repel each other. With increasing pressure the nuclei get closer to each other. Electrons orbital shells overlap and are no longer associated with specific nuclei so the core becomes electron degenerate matter. Atomic nuclei have positive charges and also repel each other. Normally iron nuclei with mixed protons and neutrons surrounded by electrons would be lower energy than the same mass of neutrons. If the atoms are squeezed enough the force repelling the charged nuclei causes the energy of mixed protons/electrons/neutrons to be higher than an all neutron state. Compare to a spring storing energy. Everything in the natural world tends to drop to the lowest available energy state. So the protons and electrons combine and the entire mass becomes neutron. The neutrons do not have a charge so a neutron degenerate core will be much smaller than the electron degenerate core. The transition from electron degenerate to neutron generate is what they mean by "cannot withstand its own gravitational force".

The explode part is more fun. See this video from physics girl for type II supernovas.

Type 1a supernovas are fusion bombs. The cold white dwarf (cold relative to a core) gets close to the core collapse pressure. Then a slight disturbance sets off the fusion reaction.

 

[Janus]

As the star runs out of nuclear fuel, some of its mass flows into its core. Eventually, the core is so heavy that it cannot withstand its own gravitational force.The core collapses, which results in the giant explosion of a supernova.
Source: https://www.nasa.gov/audience/forstudents/5-8/features/nasa-knows/what-is-a-supernova.html

What does it mean that the core cannot withstand its own gravitational force?

How and why the core cannot withstand its own gravitational force and then explode?

The "core" doesn't explode. When the core collapses, all the upper layers of the star also fall inward. It is the inward collapse and impact with the core that causes these layers to undergo sudden fusion and explode.

 

[Ken G]

Also, it should be pointed out that the inability to hold up against gravity has a lot to do with relativity, and how fast the particles that are responsible for the pressure are moving relative to c. When the electrons go degenerate in the core, they soak up virtually all of the kinetic energy from the ions (degeneracy drives their temperature down, causing heat transfer between ions and electrons that shifts the kinetic energy to the electrons). When the electrons have the kinetic energy, they are also responsible for the pressure, since the pressure comes from kinetic energy density at the micro level. But electrons are low mass particles, so they get moving very fast as they gain kinetic energy, ultimately reaching close to the speed of light (in high-mass cores only). That's when something very important happens-- the dynamical stability shifts from highly stable (nonrelativistic particles) to neutrally stable (highly relativistic particles going close to c). Physically, it is because if the electrons are already going at close to c, they cannot be made to go much faster as gravitational energy is released, and this compromises their ability to push back as the contraction continues.

The situation is not quite dynamically unstable when relativistic, but it's close enough that any process that loses heat (like creation of neutrons, photodissociation of nuclei, and escape of neutrinos) easily makes the core collapse catastrophically. It's all about the electrons approaching c-- degeneracy is only relevant because it robs the ions of their stabilizingly non-relativistic share of the kinetic energy that is going into the pressure. There is no role of "degeneracy pressure," indeed that is not a type of pressure at all, the term merely means the gas pressure that is present, owing to mundane kinetic energy density, when the temperature has been driven down very low as the system approaches its Pauli Exclusion Principle regulated "ground state" .

The same holds when neutronization occurs-- pressure still comes from kinetic energy density, so the "bounce" only happens because when the pressure is held by higher mass neutrons rather than lower mass electrons, the particles are less relativistic and hence more dynamically stable. However, there are still heat-loss mechanisms that would doom the neutrons to collapse, except that the system's PEP-regulated ground state is being approached, and that can cause the temperature to be made low enough that heat loss is inhibited enough that collapse cannot occur. If so, you get a neutron star, but if the heat loss is not inhibited enough to prevent further collapse, you get a black hole.