Eta Carina and the Homunculus Nebula; Credit: N. Smith, J. A. Morse (U. Colorado) et al., NASA
At the density and temperature of the center of our Sun, it will be possible for fusion to produce all elements up to magnesium in the periodic table. For a more massive star, however, it is possible for
The nuclear reactions that occur in the center of a star are very sensitive to temperature. For a star twenty times more massive than the sun, hydrogen burns through a catalytic process that is faster than the process that occurs in our sun. The core of the star ends up hotter, which is necessary to support the greater mass of the star, and as a result, it exhausts its hydrogen supply faster. For instance, the Sun will burn hydrogen for about 10 billion years. A star 10 times the mass of the sun will only live 150 million years --- about 2% as long as the Sun. The star responsible for the image above may well be 100 times the mass of the Sun, and probably has only lived lived 3 million years. It is now thought to have exhausted its supply of hydrogen, and begun burning helium.
Why does this make for such an unusual-looking "star"? When helium starts burning, things get wild, because helium burns very rapidly. Instead of simply swelling up in the way that a star like our sun becomes a red giant when it starts burning helium, a massive star will actually blow its outer layers into space. The core of the star becomes exposed, and one can see the carbon, nitrogen and oxygen that was produced by fusion in the core of the star. For a very massive star, so much energy is produced that gravity can barely hold it together. Although astrophysicists don't understand exactly why, for some reason these massive stars erupt, becoming hundreds of times brighter for years and decades at a time.
The above image show the aftermath of one of these eruptions, around the a pair of stars referred to as eta Carina. Together, the two stars in eta Carina are thought to be up to a hundred times the mass of the sun. In the early 1840's, eta Carina was the second brightest star in the sky (Now, the star is barely visible to the naked eye). At that time, it ejected more than ten times the mass of the Sun into the space around it. The structure in the image above represents material from later, smaller eruptions. The dumbbell shape probably results from the way the two stars interact.
The dramatic eruptions from eta Carina are the death throes of one of its stars. That star will burn helium for a hundred thousand years. Eventually, carbon will ignite, and be consumed in about a thousand years. Neon, oxygen, and silicon suffer the same fate in successively shorter time intervals. Eventually, the core will be composed of iron. At this point, nuclear burning no longer can produce energy, so the core of the star will collapse, triggering a supernova explosion.