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Evolution of Stars Greater Than 30 Solar Masses aka Massive Stars

Page history last edited by Nayan Walia 12 years, 2 months ago

Massive Stars

by Nayan Walia and Katlin Luu



Stars form when dense molecular clouds collapse together and form a protostar.

Massive stars arise from collapsing molecular clouds which have large amounts of Hydrogen. The initial size of a protostar determines whether or not it will be massive. Massive stars are stars whose solar masses are greater than ten. There are also extremely massive stars. Most stars do not exceed 120 solar masses, because the radiation pressure will be too high for them and would result in the obliteration of their layers, but they are extreme cases.  Today, we will focus on massive stars whose solar masses are greater than thirty. Massive stars of over 30 solar masses are also rare, as most stars are between .1 and 3 solar masses. Massive stars are very significant to our Universe. They run the interstellar medium and provide some physical properties to the red-shift galaxies.



Earth's Size Compred To Larger Stars



The Evolution

Massive stars begin as main sequence stars, but are much bigger than other main sequence stars. They are also much hotter than other stars, and are generally blue in color. This blue color is seen because of specific ions that are present in the star and are present in the absorption lines given off by the light emitted from the star.  In the center of the star, gravity begins to compress the Hydrogen atoms together, and the Hydrogen atoms which came together to form the protostar begin to fuse into Helium atoms, thus making the center slightly more dense than the outer parts of the star. The area of fusion begins to move outward, and the core begins to widen. As a result, the pressure caused by the Helium in the center begins to grow and gravity becomes stronger within the center. The gravity becomes so powerful as to force the Helium atoms to fuse together into Carbon and Oxygen. The gravity on the outer layers is weak, so the energy produced by the fusion reactions pushes out and causes the star to expand and swell. The star expands exponentially, so the pressure in the center begins to lessen. This allows the star to cool slightly and become less dense.



Heavier elements form in the core and the star continues to expand. As heavier elements fuse in the core, they eventually begin to fuse into iron.  Iron cannot fuse into heavier elements because it requires energy for the iron to burn. As iron builds up in the core, the pressure decreases until the inner core collapses. The resulting absorption of energy causes the outer layers to stop expanding. The inner core then collapses in upon itself, and the outer core collapses on the inner core. Due to the nuclear density, the core cannot completely collapse in on itself so at one point the inner core begins to expand again. It collides with the collapsing outer core and the collision releases powerful shockwaves that force the elements to fuse into uranium and blows away the outer layers of the star as energy. Most of the star’s mass is then turned into energy. As described in Einstein’s equation, E = m * c², a lot of energy can be produced from a small amount of mass. The majority of the star’s mass is converted into energy, and this energy is released very suddenly, in a large explosion called a supernova. The super dense core remains after the explosion. Particles are scattered into the surrounding cosmos.

Massive stars of over 30 solar masses will theoretically always become black holes after the supernova death. In stars of between 2 and 3 solar masses, the neutron degenerate pressure is able to stop gravity from forcing the star to completely collapse in on itself. This is a pressure produced by the neutrons of atoms, similar to electron degeneracy pressure. When the atoms are squeezed together by the force of gravity, the subatomic particles become limited in their motion and as a result, they are paired in small cells and move erratically against gravity. This erratic motion creates pressure which stops gravity from completely enveloping the core. However, in massive stars, specifically over 30 solar masses, the gravity is much stronger, the neutron degeneracy pressure is not strong enough to resist the strong pull of the gravity, and gravity forces the star to collapse in on itself. This in turn, produces a black hole.



Some of the most massive stars ever----woah!

  • HD 93250 = 118 solar mass
  • S Doradus = 100 solar mass
  • Cygnus OB2-12 = 92 solar mass
  • R 66 = 70 solar mass



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