How do supernova work?

Question

Hello everyone.

I'm quite confused as to what triggers a supernova.

If we have a star that has run out of fuel, it will contract right, because of it's gravitational attraction overcoming radiation pressure. Now, why does it suddenly explode it's outer layers off and cause only the core (which I assume is the stable part of the star such as iron) to remain? What triggers that action? And why does the temperature stop increasing when the star continues to collapse inwards (cooling)? Is there some trigger point that just activates some huge amount of unknown energy and causes a supernova? Is this the same process that will happen to a sun-like star? (I heard it shouldn't explode in such a violent manner as it's mass is not big enough. So what happens then?)

Thank you.

Answer 1

There is no "huge amount of unknown energy", the source of the energy is perfectly known: gravity. Stars are constantly collapsing in on themselves. This collapse creates such intense heat at the core that nuclear fusion begins. All the energy released from this fusion "pushes out" enough to overcome the power of gravity trying to collapse the star. Once a star runs out of material to fuse there is no longer enough energy to overcome the force of gravity and the star collapses. Once you reach a certain point even the heat generated in the core isn't enough to sustain fusion of heavier elements. Hydrogen fuses into helium, helium into carbon, and so on. Eventually a star reaches a point it can no longer fuse the elements it contains. The collapse is sudden and violent. The force of gravity diminishes with distance and stars are very big. Stars massive enough to supernova are very, very big. So the core collapses much faster than the outer layers so they lag behind enough to be blown off by the energy released by the collapsing core. The core cools off because there's no longer nuclear fusion taking place. And you heard correct, the Sun is not massive enough to become a supernova. When the Sun runs out of hydrogen to fuse in the core it will begin fusing hydrogen in the outer layers. Our Sun is not massive enough, so doesn't have enough gravity to create enough heat, to fuse elements heavier than carbon in the core. When the outer layers begin to fuse they will expand and the Sun will become a red giant. After that fuel is used up it will just collapse down into a white dwarf. It won't be violent enough to be a supernova because there's not enough gravity driving it.

Answer 2

Gravity gives the supernova its energy. Mass flows into the core by the continued formation of iron from nuclear fusion. Once the core has gained so much mass that it cannot withstand its own weight, the core implodes. This implosion can usually be brought to a halt by neutrons, the only things in nature that can stop such a gravitational collapse. Even neutrons sometimes fail depending on the mass of the star's core. When the collapse is abruptly stopped by the neutrons, matter bounces off the hard iron core, thus turning the implosion into an explosion.

Answer 3

Here is what is so cool about Genesis. It was written long before man had a scientific understanding of the universe. Yet the sequence of events as stated by Genesis and science is the same. For example, both Genesis and science place the following events in the same order: Creation of light (the big bang), the creation of our sun, the creation of plants, creation of sea animials, creation of land animals, creation of man. I just don't get why more people don't realize that science and Genesis both teach us about the origins of life, just from a different point of view. I can only imagine that too many people get hung up on the idea of the 7 'days' of creation being 7 24-hour periods. This is logically ludicrous. For starters, a modern 'day' is defined as the time it takes to have the earth rotate once. So how can you measure days before the earth is created? Next, Genesis sort of pauses between each 'day' to allow for evening to come followed by morning. The 'problem' is that it is ALWAYS moring, noon, evening, and night all at the same time SOMEWHERE on the earth. So how can you talk about the creation of the earth in terms of the days being seperated by evening and morning? So to me, Genesis CAN NOT be taken litterally because it logically does not fit together. But here is what I do see. Genesis being written by a man (that didn't know the world was round) limited to his understanding of the natural world. But devinely inspired because so much of Genesis and science parallel each other.

Answer 4

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Stars are sustained by the nuclear fusion reactions taking place in their cores. For stars on the main sequence, such as our own Sun, this mostly involves combing hydrogen to form helium. The energy that these reactions produce is enough to support their mass against its own gravity.



As a star runs out of fuel it can expand and will begin to form heavier elements such as carbon and iron (most of the matter in our solar system comes from extra-solar sources). Once it finally exhausts all of its fuel it will begin to collapse. It is here that the stars begin to undergo different fates.



Our own sun will collapse until it becomes a white dwarf, at this point the Pauli exclusion principle keeps the electrons in the star far enough apart to resist further collapse - this energy is called 'electron degeneracy'.



Stars greater than 1.4 times the mass of the Sun (called the Chandrasekhar limit after the Indian physicist who discovered it on his way to England) will tend to explode in a supernova casting off much of their mass. A small central core will remain and like smaller stars this will collapse only this time electron degeneracy will not be enough to support the star's mass against its gravitational collapse and it will continue to shrink until it becomes a tiny, but hugely massive, neutron star held together by neutron degeneracy.



If neutron degeneracy is not enough to resist the star's collapse it will continue to shrink until the matter is all compressed into an infinitely small, infinitely dense point called a singularity. This is the centre of a black hole.

Answer 5

The fusion of iron is an endothermic reaction. The drop in temperature removed the support against gravity and the star collapses. For large stars the pressure exceeds the electron degeneracy pressure and electrons are forced into protons to create neutrons and neutrinos. Lot and lots and lots of neutrinos. It is the force of the neutrinos that cause the explosion.

Answer 6

When a sun runs out of Hydrogen, there is nothing left to burn so gravity ends up taking over and crushing the core of the super massive sun and it crushes is so much the sun implodes and collapses on itself resulting into a massive explosion also known as a Super Nova.