The calculation models the collapse and fragmentation of a molecular cloud with a mass 50 times that of our Sun. The cloud is initially 1. In a newly formed star cluster, there are many more stars with low masses than stars with high masses. For every star with a mass between 10 and solar masses, there are typically 10 stars with masses between 2 and 10 solar masses, 50 stars with masses between 0.
As time passes the balance shifts even more toward smaller stars because the higher mass ones die first. Stars above about solar masses generate power so furiously that gravity cannot contain their internal pressure.
These stars blow themselves apart and do not exist for long if at all. Examples of protostar in a Sentence Recent Examples on the Web This creation story begins more than 4. First Known Use of protostar , in the meaning defined above. Learn More About protostar. Time Traveler for protostar The first known use of protostar was in See more words from the same year. Statistics for protostar Look-up Popularity. Style: MLA. More from Merriam-Webster on protostar Britannica.
The gas is mostly made up of atoms of hydrogen, though small amounts of heavier elements can be found floating through space, as well. In some places, the interstellar medium is collected into a big cloud of dust and gas called a nebula. A nebula can be many light years across. It is in these nebulae that dust and gas can come together to form stars. A star is not truly a star until it can fuse hydrogen into helium. Before that, they are called Protostars. So, the energy released is:.
You can use this information to estimate the lifetime of the Sun or any other star in the following simple way:. This ignores several important details, but for a typical Sun-like star, you determine that it can shine by hydrogen fusion for approximately 10 billion years.
So, now that we know how energy is generated inside a star via nuclear fusion, we can answer the following question: Why does the onset of nuclear fusion signal the transition of a protostar into a true star? The answer is that the nuclear fusion generates energy, and this energy provides enough radiation pressure to finally balance the inward pull of gravity, stopping the contraction that began when the clump of gas began to collapse in on itself.
The energy generated in the star is being radiated outwards as photons of light. As the photons pass through the star, they created a net outward push radiation pressure , which along with the thermal pressure of the material in the star, resists gravity. When the force of gravity is exactly balanced by the total pressure, we say that the star is in hydrostatic equilibrium. There are several final points that should be mentioned on this page.
The temperature that the core of a protostar reaches depends on its mass. The more massive the protostar, the hotter it gets. If the core reaches a high enough temperature more than 20 million kelvin , a different set of fusion reactions proceed more efficiently than the proton-proton chain. This process, called the CNO carbon-nitrogen-oxygen cycle , occurs in stars more massive than the Sun.
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