Free Astronomy Magazine September-October 2020

51 SEPTEMBER-OCTOBER 2020 SPACE CHRONICLES answer. The ALMA and VLA map of Antares is the most detailed radio map yet of any star, other than the Sun. ALMA observed Antares close to its surface (its optical photos- phere) in shorter wavelengths, and the longer wavelengths observed by the VLA revealed the star’s at- mosphere further out. As seen in visible light, Antares’ diameter is ap- proximately 700 times larger than the Sun. But when ALMA and the VLA revealed its atmosphere in radio light, the supergiant turned out to be even more gigantic. “The size of a star can vary dramat- ically depending on what wave- length of light it is observed with,” explained Eamon O’Gorman of the Dublin Institute for Advanced Stud- ies in Ireland and lead author of the study published in Astronomy & Astrophysics . “The longer wave- lengths of the VLA revealed the su- pergiant’s atmosphere out to nearly 12 times the star’s radius.” The radio telescopes measured the temperature of most of the gas and plasma in Antares’ atmosphere. Most noticeable was the tempera- ture in the chromosphere. This is the region above the star’s surface that is heated up by magnetic fields and shock waves created by the vigor- ous roiling convection at the stellar surface – much like the bubbling G raphic scheme of the atmosphere of Antares. As seen with the naked eye (up until the photosphere), Antares is around 700 times larger than our sun, big enough to fill the solar system beyond the orbit of Mars (Solar System scale shown for comparison). But ALMA and VLA showed that its atmosphere, including the lower and upper chromosphere and wind zones, reaches out 12 times farther than that. [NRAO/AUI/NSF, S. Dagnello]