A Wolf-Rayet nebula is a type of

nebula A nebula (; or nebulas) is a distinct luminescent part of interstellar medium, which can consist of ionized, neutral, or molecular hydrogen and also cosmic dust. Nebulae are often star-forming regions, such as in the Pillars of Creation in ...

created from

stellar winds A stellar wind is a flow of gas ejected from the upper atmosphere of a star. It is distinguished from the bipolar outflows characteristic of young stars by being less collimated, although stellar winds are not generally spherically symmetric. Di ...

expelled by Wolf-Rayet stars. Wolf-Rayet stars are very hot, highly luminous, and rapidly evolving massive stars that are fusing

helium Helium (from ) is a chemical element; it has chemical symbol, symbol He and atomic number 2. It is a colorless, odorless, non-toxic, inert gas, inert, monatomic gas and the first in the noble gas group in the periodic table. Its boiling point is ...

or heavier elements in their cores.

Characteristics

The strong, dense

from Wolf-Rayet stars consist of streams of charged particles traveling at speeds of thousands of kilometers per second. These winds slam into the surrounding interstellar medium, generating shock waves that heat and ionize the gas and dust, causing it to glow and emit radiation in visible and other

wavelengths In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats. In other words, it is the distance between consecutive corresponding points of the same '' phase'' on ...

. This process creates an enveloping nebula around the Wolf-Rayet star with a distinctive multi-ring structure. The nebula contains shells and cavities carved out by the stellar winds, surrounded by dense swept-up material. These structures become visible due to fluorescent emission from ionized gas as well as scattered starlight.

Notable examples

Some well-studied Wolf-Rayet nebulae include: * NGC 6888 (Crescent Nebula) * NGC 2359 (Thor's Helmet Nebula) * M1-67 (Luminous Blue Variable Nebula) * NGC 3199 (Nebula around WR 18) These nebulae exhibit intricate structures revealed in visible light as well as infrared, X-ray, and other wavelengths, providing insight into the powerful stellar winds and evolutionary processes around Wolf-Rayet stars.

Formation and evolution

Wolf-Rayet stars represent a brief late stage in the evolution of some very massive stars. They have shed their outer hydrogen envelopes and their stellar winds now consist of heavier elements like helium, carbon, nitrogen, and oxygen. As a Wolf-Rayet star evolves and loses mass, its winds shape the surrounding gas and dust into bubble-like nebular structures. The inner region forms from the current stellar wind, while outer shells are remnants of previous mass-loss episodes. Eventually the star will shed more matter, ending its life in a spectacular supernova explosion that will dramatically alter the Wolf-Rayet nebula's structure and composition.

References

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