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- Just as during formation, when the material contracts, the temperature and pressure increase. This newly generated heat temporarily counteracts the force of gravity, and the outer layers of the star are now pushed outward. The star expands to larger than it ever was during its lifetime -- a few to about a hundred times bigger.
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Star formation is a complex process, beginning from cold clouds of gas and dust and ending with the diverse population of stars we observe in our galaxy and beyond. Studying that process requires many different types of astronomical observations to capture the composition, dynamics, and other properties of star-forming regions.
New stars form from large, cold (10 degrees Kelvin) clouds of dust and gas (mostly hydrogen) that lie between existing stars in a galaxy. Usually, some type of gravity disturbance happens to the cloud such as the passage of a nearby star or the shock wave from an exploding supernova.
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 around ten or more times the mass of the Sun can explode in a supernova as their inert iron cores collapse into an extremely dense neutron star or black hole.
Apr 11, 2022 · The basic idea of triggered star formation is this: when a massive star is formed, it emits a large amount of ultraviolet radiation and ejects high-speed gas in the form of a stellar wind. This injection of energy heats the gas around the stars and causes it to expand.
- A Giant Cloud of Gas. Stars begin their life cycles as clouds of gas and dust within a vast expanse of stellar debris called a nebula, formed from the gas and dust expelled by the explosion of a dying massive star.
- The Protostar. In the second stage of a star's life cycle, the giant gas cloud collapses in on itself forming a protostar. The matter at the center of the cloud compresses into a hot, dense core.
- The T-Tauri Star. The T-tauri stage, named for a star discovered in the Taurus constellation way back in 1852, begins once a protostar has collected enough material from the surrounding dust cloud to trigger a process called gravitational collapse.
- The Main Sequence. After a hundred million years of gravitational collapse a T-tauri star's core reaches one million degrees Kelvin, igniting a fusion reaction.
When the helium in the star’s core is used up, the core again collapses, causing it to heat up. A thin shell of helium around the core begins fusion, with a shell of fusing hydrogen lying just outside that. Again the star expands, its surface cools, and the star brightens.
Apr 11, 2022 · When you take the lid off a pot of boiling water, the steam can expand and it cools down. In the same way, the expansion of a star’s outer layers causes the temperature at the surface to decrease. As it cools, the star’s overall color becomes redder.
