Astronomers have taken a remarkable photo of the surface of the bright but distant star Antares, and mapped the turbulence in its vast atmosphere.
Stars normally appear only as points of light, but the team used state-of the-art techniques to image the disk of the star, a red supergiant in the constellation of Scorpius.
They combined the light collected by instruments making up the Very Large Telescope Interferometer (VLTI) operated by the European Southern Observatory in Chile to take the photo.
It has given them the most detailed picture of a star ever, which ESO say is the best image of the surface and atmosphere of any star other than the Sun.
Antares is the 15th brightest star in the night sky and its name means “rival of Mars” because it can be confused with the red planet when it passes close by.
The star lies 550 light-years away from Earth, and is expected to explode as a brilliant supernova some time in the future.
The study of Antares was made by Professor Keiichi Ohnaka, of the Universidad Católica del Norte in Chile, with astronomers at the Max Planck Institute for Radio Astronomy in Germany.
The team used ESO’s telescopes with an instrument called AMBER (Astronomical Multi-BEam combineR) to take separate snapshots of Antares’ surface at near-infrared wavelengths.
By combining these, they were able to measure how fast the star’s atmospheric gases were travelling across its entire surface. It is the first time that this has been done for any star other than the Sun.
The studies will help astronomers find out how stars like Antares go on a “crash diet” as they near the violent end of their lives.
Professor Ohnaka said in a statement: “How stars like Antares lose mass so quickly in the final phase of their evolution has been a problem for over half a century.
“The VLTI is the only facility that can directly measure the gas motions in the extended atmosphere of Antares — a crucial step towards clarifying this problem. The next challenge is to identify what’s driving the turbulent motions.”
He added: “In the future, this observing technique can be applied to different types of stars to study their surfaces and atmospheres in unprecedented detail.
“This has been limited to just the Sun up to now. Our work brings stellar astrophysics to a new dimension and opens an entirely new window to observe stars.”
Skymania News asked Professor Ohnaka if he was planning do further imaging of Antares to see how its surface, and “star spots”, change over time, or whether this had already been done.
He told us: “In 2013 we published an article, where we presented changes in the surface and atmosphere of Antares from observations taken one year apart. However, at that time, the resolution (sharpness of the image) was not as good as the present work. To get another image of Antares of the same quality as the present one is one option we have on our mind.
In 2009, French astronomers used three telescopes forming the Infrared Optical Telescope Array (IOTA) on Mount Hopkins, Arizona, to take a similar picture of the surface of another red supergiant, Betelgeuse in Orion, which lies 495 light-years away. We asked Professor Ohnaka how his observations compared to the studies of Betelgeuse.
He replied: “Both Betelgeuse and Antares are red supergiants, and similar. On the one hand, they (the French team) detected two spots on the surface, as we see in our images. On the other hand, unlike our data, their image does not have spectral information, which tells us not only at what altitude of the atmosphere the spots appear but also the velocity of the material.
“From our images, we can say that the two spots appear in the upper part of the atmosphere (at high altitudes of up to 1.7 times the radius of the star). Furthermore, we found vigorous turbulent motion in that part, which is the first study to do so in a star other than the Sun.
The results are reported today in a paper, Vigorous atmospheric motion in the red supergiant star Antares, published in the journal Nature.
Related: Betelgeuse seen in stormy close-up
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