Yellow hypergiants are rare stellar objects, only a dozen have been identified in the Milky Way, so all are considered cosmic jewels. The yellow hypergiant is actually a short phase that some of the most massive stars (depending on their mass) go through before burning all their fuel reserves. During this phase, violent internal convulsions blast huge quantities of stellar gases into space, creating a vast nebula around the star.
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Although it's located moderately far from Earth, HR 5171 can just about be seen on a clear night in the constellation of Centaurus with the naked eye and has been measured to have a magnitude of between 6.10 and 7.30.
Over the last 40 years HR 5171A has been growing bigger, becoming cooler as it expands. Its adjoined stellar partner HR 5171 B is slightly hotter and has been observed to pass in front of HR 5171 A as they carry out their intimate orbital waltz (it is for this reason HR 5171 is known as an "eclipsing binary" system), a relationship that inevitably affects the dynamics of the system's lifecycle.
"The companion we have found is very significant as it can have an influence on the fate of HR 5171 A, for example, stripping off its outer layers and modifying its evolution," said Chesneau.
For more on the fascinating history of HR 5171 and high resolution images of the eclipsing binary, browse the ESO news release.