Astronomers from Belgium and the Netherlands believe they have discovered the origin of mysterious blue light coming from the hypergiant star HR 5171A.
The binary star system HR 5171 is the bright object just below the center of this wide-field image. Image credit: Digitized Sky Survey 2 / ESO.
HR 5171A, also known as HD 119796A or V766 Centauri A, is a yellow hypergiant located in the constellation Centaurus, approximately 12,000 light-years away.
It is one of the ten largest stars found so far. It is 50 per cent larger than huge Betelgeuse and about a million times brighter than the Sun.
HR 5171A is part of a binary star system, with the second component (HR 5171B) so close that it is in contact with the main star.
The two stars are so close that they touch and the system resembles a huge peanut.
HR 5171A’s enigmatic blue light was accidentally observed in the 1970s by Leiden Observatory astronomer Dr Arnout van Genderen, but without providing a good explanation for it.
More than four decades later research by Dr van Genderen and his colleagues, Dr Alex Lobel from the Royal Observatory of Belgium and Dr Hans Nieuwenhuijzen from SRON Laboratory for Space Research, reveals the light was caused by PAH (polycyclic aromatic hydrocarbon) molecules.
“PAHs are ring-shaped molecules. They are observed in large gas clouds in specific conditions between and near stars,” the astronomers said.
“On Earth the molecules form by incomplete combustion of fossil fuels. In the Milky Way they are observed in dusty nebulae.”
The results were published in the journal Astronomy & Astrophysics (arXiv.org preprint) in November 2015.
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A. M. van Genderen et al. 2015. An early detection of blue luminescence by neutral PAHs in the direction of the yellow hypergiant HR 5171A? A&A 583, A98; doi: 10.1051/0004-6361/201526392
