A unique supergiant star

What you see in this photo is a red supergiant star expelling a cloud of gas and dust as it nears the end of its life. These nebulae are common around supergiant stars; however, this particular cloud presents an unexpected and considerable mystery for astronomers. 

This is the largest cloud of ejected material to have been found around a supergiant star, at an enormous 1.4 light years across. Astronomers studied this star, Stephenson 2 DFK 52, with the Atacama Large Millimeter/submillimeter Array (ALMA) while studying other supergiants in its vicinity. DFK 52 is rather similar to Betelgeuse, another famous red supergiant, so they were expecting to see a similar cloud around it. However, if DFK 52 was as close to us as Betelgeuse is, the cocoon around it would be as wide in the sky as a third of a full Moon.  

These new ALMA observations allow astronomers to measure the amount of material surrounding the star and its velocity. The parts that are moving towards us are highlighted in blue, and the sections that are moving away are highlighted in red. The data show that about 4,000 years ago, the star went through an episode of extreme mass shedding, and then slowed down to its current rate, more similar to that of Betelgeuse. DFK 52 is estimated to be 10-15 times more massive than the Sun, and by now it has already lost 5-10% of its mass. 

It’s still a mystery as to how the star managed to expel so much material in such a short timeframe. Could it be an odd interaction with a companion star? Why is the shape of the cloud so unusually complex? Are there more supergiants like this out there? Deciphering why DFK 52 has already shed so much material will help astronomers understand how it will meet its end: a supernova explosion sometime in the next million years. 

Additional Information

The research paper is accepted for publication in Astronomy & Astrophysics as "Stephenson 2 DFK 52: Discovery of an exotic red supergiant in the massive stellar cluster RSGC2" by Siebert et al.

This article is based on a picture of the week issued by the European Southern Observatory (ESO), an ALMA partner on behalf of Europe.

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Southern Observatory (ESO), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the National Science and Technology Council (NSTC) in Taiwan, and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of ALMA's construction, commissioning, and operation.

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