BioEd Online

In a stellar version of the tale of Jonah, a 'failed star' known as a brown dwarf has survived being swallowed by the fiery bloat of a red giant in its death throes.

Researchers are surprised that a celestial body so relatively small managed to survive the immensely violent event. "It lowers the limit on what size a brown dwarf can go through a red giant and survive," says Matt Burleigh, an astronomer at the University of Leicester, UK.

Before the event, the resilient dwarf probably orbited its star at about the same distance as Earth is from the Sun, the researchers say.

But sadly, the results don't imply that Earth, which is much smaller than a brown dwarf, will survive our own star's death some 5 billion years from now. Our planet will probably be sucked in and destroyed by the Sun's final gasps, the researchers say. Jupiter, though, will probably make it, says Burleigh.

Star struck

The resilient brown dwarf is about as large as Jupiter, the biggest planet in our Solar System, but about 55 times more massive.

Commonly known as a failed star, a brown dwarf is too small to maintain hydrogen-burning nuclear reactions and so is relatively cool in temperature, at just 1,500 °C.

When this dwarf's companion, Sun-like star grew old, it expanded into an immense searing object known as a red giant, whose envelope of hot gas would have engulfed the brown dwarf and sucked it in to a closer orbit. At the end of this period the red giant left behind only a lifeless core, known as a white dwarf, around which the surviving brown dwarf was left in orbit.

As seen today, the two planet-sized stars zip around each other in just 2 hours.

Pierre Maxted from the Keele University in Staffordshire, UK, and his team spotted the unusual system using the European Southern Observatory's Very Large Telescope in Chile. Their findings are reported in this week's Nature¹.

By measuring the parameters of the system's orbits, the team could extrapolate how the unique double-act came into being. They say there is no way that the brown dwarf could have begun its life where it is now, as that lies within the boundaries of the original Sun-like star.

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