Larger stars, from about 3 or 4 solar masses upwards, follow a similar route to medium mass stars but on an express schedule! They burn their way through the hydrogen in the core and become red giants. Depending on mass, this can take a few billion or only millions of years; the heavier the star, the shorter its life. They then burn their helium. Once the helium becomes exhausted, leaving mainly carbon and some oxygen in the core, the extra mass allows further contraction, and, therefore, still higher temperatures. This allows the star to start converting carbon into heavier elements up to iron; for example, oxygen, neon, silicon, sulphur, and iron. How far this progresses depends on the mass of the star. If the star looses a large proportion of its mass, bringing it down to less than 1.4 solar masses, it could form a white dwarf, but this would not comprise helium, but a combination of oxygen, neon, and magnesium.
Nuclear reactions to convert iron into heavier elements require an input of energy, so the star’s evolution stops here. Because it is not producing any energy in the core, the collapse under gravity continues forcing electrons to combine with protons to form neutrons. Surrounding material is falling into the core, which is unable to contract further, so the matter is “bounced” off the core. This results in the star going Supernova, simultaneously producing an abundance of neutrinos.
This is a spectacular explosion, and for a month or so, the star shines brighter than all the other stars in its galaxy put together. Much of the heavy elements produced in the star are ejected into space, and the explosion is so energetic that it makes elements heavier than iron. Later populations of stars that form from nebulae incorporating this expelled matter start with heavier elements. This is also true of the dust that accretes around them, and from which planets, like the Earth, could one day form. Every atom of elements other than hydrogen and helium has been formed inside stars, and through supernova events. All the carbon, iron, calcium, oxygen etc in our bodies was made by stars since the Big Bang. Thus, it is true to say that “we are stardust"!
The core now becomes a ball of neutrons; like a super-sized atomic nucleus. If its mass is less than about 1.4 solar masses, it becomes a neutron star. Any heavier, and the neutron degeneracy pressure is insufficient to stop further collapse to a black hole. In the case of really massive stars, the supernova may generate an energy level that is more than the star's gravitational binding energy. This pair-instability type of supernova destroys the star completely, leaving no remnant; the entire star is blasted into space.
Here are a few examples of massive stars, and what is likely to happen to them in the future:
High Mass Stars
Astronomy & Cosmology -
Stars - Life & Death of Stars
The Pistol Star, seen here shining in the center of the Pistol Nebula that it created. It is thought to have been around 200 solar masses before it created the nebula by blowing off part of its outer shell, and now weighs between 80 and 150 solar masses. It is between 300 and 340 times the size of the Sun, 25,000 light-years away, and about two million years old. It will probably go supernova within one to three million years.
BetelgeuseBetelgeuse is a very bright star in the constellation Orion, and weighs about 20 solar masses. It is about 1,189 times the diameter of the Sun, and only about 10 million years old. It has shrunk 15% since 1993, which is probably the start of its' contraction prior to becoming a supernova in, perhaps, 1 million years time. It is a Type M2 semi-regular variable about 643 light-years away.
The Eta Carinae binary system is much larger, with the primary being more than 100 solar masses. It is in the center at the intersection of the two globular clouds that are the result of a supernova imposter event, seen on Earth in 1843. It is between 85 and 195 times the diameter of the Sun, c. 7,500 to 8,000 light-years away, and about two to three million years old. It will probably go supernova within the next million years, and possibly much sooner.