Massive stars live fast, and die young! They follow the same sort of evolution as low mass stars (except that they are so luminious that they are called supergiants rather than red giants) up to the point where the low mass star had a carbon core. For stars smaller than about 6x the mass of the Sun then this is the end since their gravity is not strong enough to heat the core up enough to start other nuclear fusion reactions. But in higher mass stars gravity is stronger, so the core temperature can rise so that the star can fuse Helium onto carbon to get oxygen and Helium onto oxygen to get Neon, and Helium onto Neon to get Magnesium.... all the way up the periodic table in steps of 2 (since the Helium nucleus has two protons), making all the heavy elements by nucleosynthesis forming shells of fusion reactions around the core.
But there must be a problem somewhere, since we know we can get energy
from FISSION (splitting apart) of high atomic number elements (atomic
number is just the number of protons in the nucleus) like uranium.
Uranium doesn't give us energy is we add a Helium nucleus on - it
gives us energy if we take one away!!! There must then be a crossover
point somewhere, where we get very little energy for either fusion or
fission. This crossover is at iron. When the star starts fusing lower
atomic number elements into iron then the iron core just builds
up. There are no more sources of fusion energy. The iron core
contracts and heats up, but there is nowhere to go to get energy. In
the end it is held up by electron degeneracy pressure, but the iron
ash from
How much mass can the electron degeneracy pressure hold ? When gravity can only be balanced if the average electron is moving at the speed of light then it all goes horribly wrong (Einsteins theory of special relativity - but ignore the maths), says that the speed of light is always the speed of light and that NOTHING can go faster. Which is very odd - if I am in a plane going at 500 mph and I throw a ball to another passanger at 10 mph then to someone on the ground the ball is moving at 510 mph. But if I now swap the ball for a torch, then the photons go between me and the other passanger at the speed of light, but Einstein said that the person on the ground has to also see the photons going at the speed of light NOT the speed of light + 500 mph! Since speed is distance/time then the only way for this to work is if either distance has gone strange, or time has gone strange, or both have gone strange - in fact its BOTH. Space and time go strange when you get to speeds close to the speed of light.
For a CORE mass (the initial star mass can be much larger as it loses some of its outer layers) of about 1.4x the mass of the Sun the electrons can't take any more. The core collapses catastrophically , falls in, bounces, and the explosion tears apart the outer layers of the star in a dramatic supernova explosion - and more pictures of supernovae .
The energy released in this explosion is huge, leading to temperatures which are high enough to fuse higher atomic number elements, even though this takes energy, rather than providing energy. All the elements formed in the star get scattered across space in the explosion: this is the way in which the elements heavier than Helium formed (including those in us)!!
But what happens to the core ? The collapsing electrons get close enough to the protons to find life easier if they interact, forming a neutron (and a neutrino). Neutrons are like electrons in that they don't like being stuck in a box either, but they are more massive particles, so they have more energy, so the wavelength associated with them is smaller. So they can fit in a much smaller box. This is a neutron star , held up by neutron degeneracy pressure. But again, there is a limit to the mass of the stellar core which can be held up by this - when the mass is so big that gravity can only be balanced by neutron degeneracy pressure from neutrons approaching the speed of light. It all goes horribly wrong (again), but the core has nowhere left to go. A white dwarf has the mass of the Sun, squashed into an object the size of the Earth (the Earths diameter is 100x smaller than the Sun's). A neutron star is 2000x smaller than a white dwarf, so we have the mass of the Sun, squashed into a region the size of Newcastle (10 km diameter). And now gravity is very very strong. We have only to squash a neutron star by another factor of 3 before the gravity is so strong that light cannot escape. This is the definition of a black hole, space so warped that even light is forever trapped inside.
This is quite a big difference between Einstein and Newton's ideas
of gravity. Newtons gravity affects
anything with mass. so we might not expect light to be affected by it!
But while Newton is great at giving us ways to calculate the effects
of gravity, he is entirely silent on what it actually is - his gravity
is a spooky 'action at a distance' force which is
INSTANTANEOUS (ie travels faster than the speed of light!). Einstein
solved this in his general theory of relativity, giving us
better ways to calculate gravity (which doesn't now go faster than
light!). But even more importantly his theory gave us ways to THINK
about gravity as curved space(time). Everything that travels across
space(time) is affected by the LOCAL curvature of space(time). So
gravity affects light.
see Kuhn p449-457