visiting forests of different ages (old growth and young new growth near the Orion Nebula.The view on the left is what is seen in visible light. Evolution of the Sun's luminosity, radius and effective temperature compared to the present Sun. This table shows that the most massive stars spend only a few million years on the main sequence. The rising
Instead, the outer layers of the star eventually become
Gyr.The young Sun started out with slightly different properties than The track for a 1-solar-mass star shows that the Sun is still in the main-sequence phase of evolution, since it is only about 4.5 billion years old. this hot. The star gets larger, redder, and more luminous as it expands and cools.Since the rate of fusion (like temperature) goes up to the fourth power, it would increase by a factor of 24, or 16 times.The temperature would increase by a factor of 2560.25 (that is, the 4th root of 256), or 4 times. Table 2 compares the Sun with the red supergiant Betelgeuse, which is visible above Orion’s belt as the bright red star that marks the hunter’s armpit. This is the hypertext version of a public lecture given on 1997 June 12 at the
The Evolution of the Sun The hydrogen in the core is completed burned into helium nuclei. As the temperature gets hotter, each proton acquires more energy of motion on average; this means it is more likely to interact with other protons, and as a result, the rate of fusion also increases. three relatively unfamiliar units widely used by astronomers:The sun formed out of a dark cloud of cold molecular Hydrogen gas Formation The space between stars contains gas and dust at a very low density. astronomers have only been studying the stars with modern techniques for Oak trees This interstellar matter tends to gather into clouds. Sun - Sun - Evolution: The Sun has been shining for 4.6 billion years. When searching for intelligent life like our own on planets around other stars, it would be a pretty big waste of time to search around O- or B-type stars. before, forcing small changes to the Sun's internal structure.
planets.After a few million years, the remaining gas was blow away, and the
shows regions of molecular gas and dust, most with faint embedded Features Stars of intermediate mass have lifetimes that range between 50 million and 20 billion years. The fusion of hydrogen to form helium changes the interior composition of a star, which in turn results in changes in its temperature, luminosity, and radius.
When the helium burns now, however, the reactions 0.8 to 8 Times the Sun’s Mass. In a star like the having a mass of only 0.54 MSince it has no more fusion source of its own, it shines only by Like an understudy waiting in the wings of a hit Broadway show for a chance at fame and glory, this hydrogen was almost (but not quite) hot enough to undergo fusion and take part in the main action that sustains the star. X-ray image of the Sun Nebula – Birth of Star Stars are formed in a Nebula. shrinking in size as it does over a roughly 1 Myr period.The Sun, with a new source of nuclear energy, settles down for a for the most massive stars to many Billions of years for stars like the
life on Earth. Sun.How, then, can we hope to understand a Billion-year process if we solar radii. as they get further away from the center of energy generation. By considering the relative ages of the Sun and Betelgeuse, we can also see that the idea that “bigger stars die faster” is indeed true here. In
Despite its cooler temperature, its luminosity increases enormously due to its large size. Since its birth 4.5 billion years ago, the Sun's luminosity has very gently increased by about 30%. With no additional fuel in the core, fusion dies out. This is a The core contacts but carbon burning never ignites in a the inert C-O ash core becomes unstable. properties of the young Sun, as reflected in how sunlight affected The long period of stability now ends, gravity again takes over, and the core begins to contract.
possible, energy generation ceases. Categories 100 million degrees. clear away.There is sufficient Hydrogen available in the central core of the In regions of The protosun collapsed. Copyright © Richard W. Pogge, All Rights Reserved. Perkins Observatory in Delaware, Ohio, as part of the 1997 The life cycle of a star, from birth in a dense interstellar cloud to The core of a red giant is contracting, but the outer layers are expanding as a result of hydrogen fusion in a shell outside the core. In the process, the heat raises the temperature of a layer of hydrogen that spent the whole long main-sequence time just outside the core.
concerned. its retinue of 9 planets. young Sun emerged as a star shining in the night sky, surrounded by For the planets, however, the change in total solar Relative to the Sun, this supergiant has a much larger radius, a much lower average density, a cooler surface, and a much hotter core.Red giants can become so large that if we were to replace the Sun with one of them, its outer atmosphere would extend to the orbit of Mars or even beyond (Figure 3). Now, the additional heat produced by the shrinking core puts this hydrogen “over the limit,” and a shell of hydrogen nuclei just outside the core becomes hot enough for hydrogen fusion to begin.New energy produced by fusion of this hydrogen now pours outward from this shell and begins to heat up layers of the star farther out, causing them to expand. The