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Astronomers have just mapped the surfaceof Antares This is our bestyet image of a star that’s not the Sun. Astronomers havemapped the surface of the star Antares in unprecedented detail, producing thebest image of a star’s surface to date other than our Sun. ESO/K. Ohnaka When you look up into the night sky, youcan spot thousands of stars from a dark location on a given night. But thosestars only appear as pinpricks of light to the human eye; unfortunately, theylook much the same to advanced telescopes as well. While nebulae and clusterscan span hundreds of light-years, a single star alone is quite small. In thepast, this left astronomers with but one star whose surface could be studied inany real detail: the Sun. But now, a team of astronomers has combined threetelescopes to map the surface of another star: the red supergiantAntares.
Their work, published August16 in Nature, utilizes theEuropean Southern Observatory’s Very Large Telescope Interferometer (VLTI) inChile to create the best yet image of the surface of a star that is not ourSun. The data was taken in near-infrared light with the VLTI’s AMBER instrumentto achieve a resolution seven times smaller than the star’s angular diameterand almost 12 times smaller than its full atmospheric extension. As a result,the team was able to measure the speed of gas moving across the face of thestar, a feat that has only ever been achieved for our Sun before now.
The results show that Antares’ atmosphere contains several clumps of gas andextends farther from the star than expected, nearly two times the star’sradius. Convection alone, which is the rising of heated gas and the sinking ofcooled gas, does not explain the extension of the atmosphere to such greatdistances. This suggests a different, as-yet-unexplained process at work in themassive star’s atmosphere.
The astronomers also determined that mass loss experienced by supergiant stars,which often shed several solar masses’ worth of material before they explode,is occurring farther from the star than 1.7 stellar radii. When a star goessupernova, that lost mass lights up as the shock wave from the explosion tearsthrough it, leaving behind the stunning supernova remnants we see.
Keiichi Ohnaka, an astronomer at the Universidad Católica del Norte in Chileand the lead author on the paper, said in a press release, “How stars likeAntares lose mass so quickly in the final phase of their evolution has been aproblem for over half a century. The VLTI is the only facility that candirectly measure the gas motions in the extended atmosphere of Antares — acrucial step towards clarifying this problem. The next challenge is to identifywhat's driving the turbulent motions.”
Similar activity has been seen in the atmosphere of the supergiant starBetelgeuse in the constellation Orion, but Antares’ atmosphere appears evenmore turbulent. Betelgeuse was imaged using the Atacama LargeMillimeter/submillimeter Array earlier this year Taken insubmillimeter wavelengths with ALMA, this is the highest-resolution image ofthe star ever taken. ALMA(ESO/NAOJ/NRAO)/E. O’Gorman/P. Kervella Antares is a red supergiant star locatedabout 550 light-years away with a mass of about 12 times that of our Sun. Itwill someday explode as a type II supernova, and represents a “prototypical”star of this type. It is often called the “heart” of the constellationScorpius, and is visibly red to the naked eye when spotted in the sky. In fact,the name Antares itself essentially means rival ofAres (or rival of Mars) because the star is easilymistaken for the planet Mars.
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