Science advances with our technology, both in how we are able to model objects in the Universe and in how we are able to observe them. Science also advances thanks to the creativity researchers employ in using both their models and their telescopes.

In a new paper in Astronomy & Astrophysics, an international team figured out they could use the combined observing capabilities of the Atacama Large Millimeter/submillimeter Array (ALMA) and Very Large Array (VLA) to observe the outer layers of the nearby massive star, Antares. 

With our eyes and visible-light telescopes, we only see the star’s photosphere – the layer where light is released into a mostly transparent gas to begin its journey through the Universe. ALMA, working in the millimeter and sub-millimeter wavelengths of light, could see the chromosphere that is above the photosphere, and the VLA, working in even longer radio wavelengths, could map the even-more distant Wind Acceleration Zone. This allows us, for the first time, to see these outer star layers that we are used to only seeing surrounding our own nearby Sun and allows for amazing comparisons. 

For instance, while our Sun’s chromosphere is only 1/200th of its radius at the photosphere, but they found Antares’ chromosphere extended 2.5 times the star’s radius away from the photosphere. They also found that Antares’ chromosphere is warm rather than exceedingly hot, coming in at a peak temperature of 3500℃  as compared to our Sun’s 20,000℃. These measurements will help us piece together relationships between stellar rotation rates, sizes, and other facets and the temperature profiles beyond the star’s photospheric surface. It’s a start at least, and for now, it is simply amazing that we can see the outer layers of other stars.

More Information

National Radio Astronomy Observatory news release 

“ALMA and VLA Reveal the Lukewarm Chromospheres of the Nearby Red Supergiants Antares and Betelgeuse,” E. O’Gorman et al., 2020 June 16, Astronomy & Astrophysics