How come heavier elements exists, if max fusion product is Iron?

Question

Well, we know that there was Bang and Hydrogen. Hydrogen is fusing into Helium inside stars. Let's pass over all phases of the star life, and equasions... Fusion stops at Iron.
Where did heavy elements came from?

Answer 1

One theory is that they are formed in supernovas -- you're right, fusion typically stops at iron, because the force of gravitational attraction can only squeeze together stellar molecules so far, and the binding energy per nucleon is at a maximum right around iron, anyway -- but at the point when the majority of the hydrogen fuel of a star is expended and converted to iron via several stages of fusion, the core of the star collapses in upon itself (since the energy of fusion in the remaining fuel is insufficient to counterract the pull of gravity) and the resulting rebound ejects most of the outer surface of the star with a tremendous force. It is during this period of collapse that the immense forces within the star cause further fusion to occur, creating new, more massive elements in the process, and the supernova that results spreads these elements out into surrounding space. If the star is less than 2-3 times the size of our sun, the remaining portion of the stellar core will eventually cool into a brown dwarf, and the heavy elements created in the supernova spread throughout the cosmos to become incorporated eventually in other solar systems when the debris coaslesces into a solar system somewhere. Obviously, it takes billions of years and many supernovas to create the amounts of elements higher than iron, but remember that less than 1% of the mass of the universe is made up of these elements -- current estimates place the relative amounts at around 73% hydrogen and 26% helium, with the rest of the periodic table making up the remaining 1% along with more exotic particles.

Answer 2

Fusion does not necessarily stop at Iron.
True, Iron marks the boundary between where fusion yields excess energy and where fusion yields less energy than what was required to fuse the elements in the first place, but that does not stop a star from continuing. In a desperate attempt to fight the pull of its own gravity in the last moments of a stars life much heavier elements can be fused within a star. The fusion of heavier elements only lasts for a very brief time, but even so, all the elements heavier than Iron we have in the universe today came from the last moments of a stars life.
Often times a super nova is precluded by the formation of these heavier elements and once the star explodes, these elements are scattered throughout the universe.

Answer 3

Due to the large amounts of energy released in a supernova explosion much higher temperatures are reached than stellar temperatures. Higher temperatures allow for an environment where elements up to the atomic mass of 254 are formed, californium being the heaviest known of, though it is seen only as a synthetic element on Earth. In nuclear fusion processes in stellar nucleosynthesis, the maximum weight for an element fused is that of iron, with an atomic mass of 55.845. Fusion of elements as heavy as iron is quite rare and occurs only in the largest of stars. A neutron capture process known as the s process which also occurs during stellar nucleosynthesis can create elements up to bismuth with an atomic mass of approximately 209. However, the s process occurs slowly so most of the elements heavier than oxygen that make life possible were created in supernovas.

Answer 4

Iron CAN fuse to make heavier elements, but it does not release energy in the process. When they say fusion stops at iron, they mean power generation produced by fusion stops at iron. You can supply outside energy, in a supernova for example, and force iron to fuse into heavier elements.

Answer 5

Neutrons.

First of all while iron has the highest binding energy/nucleon its should be conceivable that elements around iron could easily be formed by fusion in stars. As for heavier elements, I believe the current theory is that they are formed though a long process of neutron absorption and betas decays.

Answer 6

Fusion as an energy source in stars stops at iron. That doesn't mean that other elements can't be created by atoms smashing together at high speeds - it just means that such collisons take more energy than they create.

Supernovas are one fine source of all sorts of neato stuff.

Answer 7

Hey come on - you have discovered a new law. Expound on it!!!

Do you know about dark matter. What about all the exotic particles given off? There is so much that is not known.

Wait until the Large Hadron Collider starts work next year and then see if it stops at iron!

Answer 8

fission