Formation The most massive stars, with masses ranging from eight to roughly one hundred solar masses and of O and early B are usually found in groups called OB associations. Massive O stars have strong stellar winds, and all of these stars explode as at the ends of their lives. The strongest stellar winds release kinetic energy of 1051 (1044 ) over the lifetime of a star, which is equivalent to a supernova explosion. These winds can form dozens of light years across. Inside , the stars are close enough that their wind bubbles merge, forming a giant bubble called a superbubble. When stars die, supernova explosions, similarly, drive that can reach even larger sizes, with expansion velocities up to several hundred km Stars in OB associations are not gravitationally bound, but they drift apart at small speeds (of s−1. around 20 km and they exhaust their fuel rapidly (after a few millions of years). As a result, most of their s−1), supernova explosions occur within the cavity formed by the stellar wind bubbles. These explosions never form a visible , but instead expend their energy in the hot interior as sound waves. Both stellar winds and stellar explosions thus power the expansion of the superbubble in the interstellar medium. The interstellar gas swept up by superbubbles generally cools, forming a dense shell around the cavity. These shells were first observed in line emission at twenty-one centimeters from ,[5] leading to the formulation of the theory of superbubble formation. They are also observed in emission from their hot interiors, in optical line emission from their ionized shells, and in infrared continuum emission from dust swept up in their shells. X-ray and visible emission are typically observed from younger superbubbles, while older, larger objects seen in twenty-one centimeters may even result from multiple superbubbles combining, and so are sometimes distinguished by calling them supershells. Large enough superbubbles can blow through the entire galactic disk, releasing their energy into the surrounding galactic halo or even into the .
Formation The most massive stars, with masses ranging from eight to roughly one hundred solar masses and of O and early B are usually found in groups called OB associations. Massive O stars have strong stellar winds, and all of these stars explode as at the ends of their lives. The strongest stellar winds release kinetic energy of 1051 (1044 ) over the lifetime of a star, which is equivalent to a supernova explosion. These winds can form dozens of light years across. Inside , the stars are close enough that their wind bubbles merge, forming a giant bubble called a superbubble. When stars die, supernova explosions, similarly, drive that can reach even larger sizes, with expansion velocities up to several hundred km s−1. Stars in OB associations are not gravitationally bound, but they drift apart at small speeds (of around 20 km s−1), and they exhaust their fuel rapidly (after a few millions of years). As a result, most of their supernova explosions occur within the cavity formed by the stellar wind bubbles. These explosions never form a visible , but instead expend their energy in the hot interior as sound waves. Both stellar winds and stellar explosions thus power the expansion of the superbubble in the interstellar medium. The interstellar gas swept up by superbubbles generally cools, forming a dense shell around the cavity. These shells were first observed in line emission at twenty-one centimeters from ,[5] leading to the formulation of the theory of superbubble formation. They are also observed in emission from their hot interiors, in optical line emission from their ionized shells, and in infrared continuum emission from dust swept up in their shells. X-ray and visible emission are typically observed from younger superbubbles, while older, larger objects seen in twenty-one centimeters may even result from multiple superbubbles combining, and so are sometimes distinguished by calling them supershells. Large enough superbubbles can blow through the entire galactic disk, releasing their energy into the surrounding galactic halo or even into the .
facts_about_different_star_stages.docx