This is the basic outline of a star's life, but scientists have to admit that they're short on details to explain the various stages. And the process repeats, creating more and more heavy elements. The ISM, enriched with the material manufactured in the star and its explosion if any, goes on to form a new generation of stars. The star may be completely destroyed, or leave behind a neutron star or - in the case of the most massive stars - a black hole. The force of the explosion converts some of those elements to still heavier elements, and that's the origin of all naturally-occurring elements heavier than iron. Very large stars end in a supernova, an extremely powerful explosion that scatters the elements it has manufactured - which could be everything up to iron - into the ISM. The core of a red giant becomes a white dwarf, while its swollen outer envelope drifts off into space, contributing whatever elements it contains to the ISM. Whatever its mass, every star eventually runs out of fuel for nuclear fusion. The most massive stars continue until finally they have iron cores. Its core, meanwhile, continues to collapse until it reaches the temperature at which nuclear fusion ignites the helium, turning it into carbon and oxygen.Ī more massive star goes on to stages in which it generates heavier and heavier elements. At sufficient temperature, nuclear fusion ignites in a shell of hydrogen around the core, creating outward pressure that causes the star's outer envelope to expand and cool. When a star about the size of our sun uses up the hydrogen in its core, the core collapses further, generating additional heat. This is known as the "main sequence," and can continue for billions of years. Nuclear fusion in the star's core turns hydrogen into helium, releasing a copious amount of energy that pushes outward and counterbalances the inward gravitational pressure of the gas. The Protostar Blows Away Its Dusty EnvelopeĮven as it contracts, the protostar develops a strong wind which gradually blows away the gas and dust in which the protostar and its disk are enveloped.Įventually, all that remains is the newly-formed star and its surrounding disk, which may clump together to form planets. This infall can happen very quickly, shrinking the protostar from the size of our entire solar system to that of Mercury's orbit in only six months. The densest parts of the cloud (known as "cores") collapse, each one forming a protostar surrounded by a slowly rotating disk of gas and dust. Some parts of the cloud become more dense than others - either by chance or by the intervention of a shock wave, which could be induced by such events as collision with another cloud, the supernova explosion of a massive star, or the gravitational attraction of a passing galaxy. It's made mostly of hydrogen generated at the beginning of the universe, and also contains helium and possibly other elements manufactured by stars. In the space between stars (the interstellar medium or ISM), a vast cloud of gas and dust collects and contracts under its own gravitational pull. The stars at left have blown away their dusty surroundings. The cold molecular clouds at right are stellar nurseries. Various stages of star formation in giant galactic nebula NGC 3603. From observing stars at various stages of development, scientists believe they have a pretty good general idea of the stellar life cycle:
0 Comments
Leave a Reply. |