9/28/2023 0 Comments Red giant particular![]() ![]() Once a star like the Sun has exhausted its nuclear fuel, its core collapses into a dense white dwarf and the outer layers are expelled as a planetary nebula. Stars with at least half the mass of the Sun can also begin to generate energy through the fusion of helium at their core, whereas more-massive stars can fuse heavier elements along a series of concentric shells. This process causes the star to gradually grow in size, passing through the subgiant stage until it reaches the red-giant phase. Later, as the preponderance of atoms at the core becomes helium, stars like the Sun begin to fuse hydrogen along a spherical shell surrounding the core. Initially the energy is generated by the fusion of hydrogen atoms at the core of the main-sequence star. Nuclear fusion powers a star for most of its existence. Over the course of millions of years, these protostars settle down into a state of equilibrium, becoming what is known as a main-sequence star. ![]() All stars are formed from collapsing clouds of gas and dust, often called nebulae or molecular clouds. The table shows the lifetimes of stars as a function of their masses. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the current age of the universe. ![]() Stellar evolution is the process by which a star changes over the course of time. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |