Astronomers have explained a “baffling” image that was taken earlier this year by the James Webb Space Telescope (JWST).

The picture, taken in July, shows a distant binary star known as WR140 surrounded by concentric geometric ripples. The WR140 binary, located just over 5 000 light-years from Earth, is made up of a huge “Wolf-Rayet star” and an even bigger blue supergiant star, gravitationally bound in an eight-year orbit.

A Wolf-Rayet star is an O-type star that is at least 25 times more mass than the Sun and is nearing the end of its life where it will likely collapse to form a black hole.

The JWST image of the binary star surprised astronomers and even triggered Internet speculation that it might be evidence of an alien megastructure light-years across.

Yet researchers have now offered a more mundane explanation. They say that the 17 concentric rings seen girdling the star are actually a series of huge dust shells created by the cyclic interaction between the pair of hot stars locked together in a tight orbit.

Each ring is created when the two stars came close together and their stellar winds – streams of gas they blow into space – meet, compressing the gas and forming dust.

“Like clockwork, WR140 puffs out a sculpted smoke ring every eight years, which is then inflated in the stellar wind like a balloon,” says Peter Tuthill from the Sydney Institute for Astronomy at the University of Sydney. “Eight years later, as the binary returns in its orbit, another ring appears, the same as the one before, streaming out into space inside the bubble of the previous one, like a set of giant nested Russian dolls.”