In 1884 he made an expedition to the shores of high-altitude Lake Titicaca in Peru, with astronomical equipment packed in by mule train. They did occasionally ensnare scientists such as Ralph Copeland. Over the following decades, astronomers began to better understand the spectra of most stellar types, but Wolf-Rayets still languished as an incomprehensible oddity. The new stars in Cygnus appeared to be something else entirely: they showed vibrant bands of bright color “more reminiscent of nebulae,” the astronomers wrote, causing them to speculate that these stars might “mainly owe their brilliance to incandescent vapors.” Ordinary stars like the sun have spectra consisting of light from across the range of visible colors, imprinted with a scattering of narrow, fine dark lines that represent wavelengths being absorbed by the chemical elements in the stars. Still, Wolf and Rayet had seen enough normal stars to know that something deeply bizarre was going on. In 1876, when French astronomers Charles Wolf and Georges Rayet first puzzled over three stars in the constellation of Cygnus, the science of spectroscopy-studying astronomical objects by spreading their light into its constituent colors-was in its infancy. Recently Wolf-Rayets have presented us with new questions about the physics that drives them, which may help solve big mysteries about the nature and fate of stars. As more observations of them arrive from powerful facilities such as the James Webb Space Telescope, this trend is repeating itself. Although their brightness makes them easy for telescopes to find, we know of only a few hundred of them in our entire galaxy.ĭespite their rarity, these enigmatic stars have a history of entanglement with the most pressing astronomical questions of the day. And because massive stars are already exceptions among star types, Wolf-Rayets are doubly rare: they are literally one star in a billion. This is a blink of the eye compared to our sun's 10-billion-year life span. Wolf-Rayet lives are measured in millions of years and sometimes much less. After a star exhausts its hydrogen, it will start burning other fuels, such as helium, but this gains the star only a modest stay of execution. The defining trait of a Wolf-Rayet star-a low abundance of hydrogen-turns out to be a harbinger of doom. Credit: NASA/ESA/CSA/STScI/Lau et al., 2022 ( left) Shashank Dholakia/Peter Tuthill ( left image processing) Yinuo Han/Peter Tuthill ( right) The photograph closely matches a numerical simulation ( right) depicting 15 successive dust shells puffed out at intervals coinciding with the system’s eight-year binary orbit. An infrared image from the James Webb Space Telescope ( left) shows the peculiar ripples of dust surrounding the WR 140 star system. They are bloated monsters with surface temperatures that can exceed 200,000 kelvins-30 times hotter than the sun-and radiation fields that can outshine the sun by factors of more than a million. Wolf-Rayets rise above and beyond the diagram's “main sequence,” where ordinary stars congregate. ![]() Their extreme nature marks them as celestial outcasts that cluster at the borders of astronomy's foundational chart, the Hertzsprung-Russell diagram, which maps stars by their brightness and temperature. When they run out of this fuel, these stars collapse under their own gravity in the cataclysmic events we observe as supernovae. As they burn up, they eject huge amounts of mass in dense, fast winds that flow at astonishing speeds. These heavyweights are blue and incredibly luminous, burning rapidly through vast reserves of hydrogen fuel with live-fast, die-young abandon. Wolf-Rayets are believed to be the final, fleeting stage in the lives of the most massive stars-those starting life with anywhere from 20 to more than 200 times the mass of the sun. ![]() Astronomers tend to exhaust superlatives when they talk about the ferociously hot and luminous stars known as Wolf-Rayets, which are among the largest, hottest and rarest stars in the universe.
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