![]() The extra mass has been converted into energy. The product of hydrogen fusion (one helium nucleus) has less mass than the four hydrogen nuclei that created it. The reason that fusion of light elements produces energy to support a star is because of the “mass defect” we discussed when we studied the proton-proton chain. At some point, the fusion reactions will create iron in the core of the star, and when this occurs, the star has only minutes to live.Ĭredit: Penn State Astronomy & Astrophysics So, it may fuse hydrogen on the Main Sequence for 10 million years, but it will only fuse helium for 1 million years, and it can only maintain carbon fusion for approximately 1,000 years. Although high mass stars can continue to fuse heavier and heavier elements, each fuel runs out more quickly than the previous one. An O star on the Main Sequence will cool and expand after it runs out of hydrogen in its core, but it will move almost horizontally towards the red supergiant region of the HR diagram as it goes from helium fusion to carbon fusion to oxygen fusion. The evolutionary track of a high mass star on the HR diagram is also different from that of low mass stars. However, in high mass stars, the temperature and pressure in the core can reach high enough values that carbon fusion can begin, and then oxygen fusion can begin, and then even heavier elements-like neon, magnesium, and silicon-can undergo fusion, continuing to power the star. In low mass stars, once helium fusion has occurred, the core will never get hot or dense enough to fuse any additional elements, so the star begins to die. When no fuel remains for this fusion sequence, and energy is no longer being released outward from those reactions, the inward force of gravity quickly wins.The lifecycle of high mass stars diverges from that of low mass stars after the stage of carbon fusion. That process repeats itself with the oxygen, converting it to neon, then the neon into silicon, and finally into iron. As the star runs low on helium, it contracts and heats up, which allows it to convert the resulting carbon into oxygen. Stars with mass eight times that of our sun typically follow a similar pattern, at least in the beginning of this phase. The explosive stellar death of a high-mass star Van Maanen’s star, in the northern constellation Pisces, is also a white dwarf. These dense stellar remnants are too dim to see with a naked eye, but some are visible with a telescope in the southern constellation Musca. It gradually cools over billions of years, emitting light that appears anywhere from blue white to red. Some of that stuff may eventually form planets, asteroids, and comets in orbit around the new star.Ībout the size of Earth, though hundreds of thousands of times more massive, a white dwarf no longer produces new heat of its own. Gravity draws even more material toward the developing star as it spins, making it bigger and bigger. The material in the middle heats up, forming a dense core known as a protostar. As that clump collapses in on itself, it starts to spin. In the beginning…Īll stars form from a cloud of dust and gas when turbulence pushes enough of that material together, pressed into one body by gravity. A star moves through various designations throughout its lifetime, an evolution shaped by its original mass and the reactions that occur within the roiling stellar body. This is largely inferred by the color of the light a star emits, which is reflected in many names given to star types.Įach category, however, is connected. Since most star temperatures can’t be directly measured, explains Natalie Gosnell, an assistant professor in physics at Colorado College, astronomers need to look at another signal: temperature. Stars in the prime of their lives, known as main sequence stars, are typically classified by how hot they are. Astronomers have identified several different types of stars in the universe, as diverse as small brown dwarfs and red supergiants.
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