The curious incident of the star that wasn’t there – Astronomy Now


In a 2010 microlensing event, the light from a background star (bright star in center and right frames) was magnified, or brightened, when a presumed main sequence star passed in front as viewed from Earth. But a search later failed to find the lensing star. Researchers concluded the event likely was caused by a white dwarf and an orbiting planet in a Jupiter-like orbit. Image: J.W. Blackman et al

Climate change aside, Earth’s long-term future is bleak. When the Sun uses up the hydrogen fuel in its core, fusion will grind to a halt, the core will contract and the star’s outer layers will expand past the orbit of Mercury. Earth will likely be engulfed by the evolving red giant in about 8 billion years as the Sun eventually becomes a white dwarf.

But what about Jupiter and the outer planets? Simulations indicate planets at Jupiter’s distance can, in fact, survive a star’s red giant phase, but observational evidence has been lacking.

Writing in Nature, a team led by J.W. Blackman of the University of Tasmania has found just such a system using microlensing, the distortion of light from a distant object by the gravity of a closer body in direct line of sight from Earth.

The microlensing event in question, known as MOA-201-BLG-477Lb, was discovered in 2010. Analysis of the light curve indicated a foreground star with 0.15 to 0.93 solar masses. The data also suggested a planet between 0.5 and 2.1 Jupiter masses. Given estimates of the lensing star’s proper motion, the researchers were able to predict where it would move with respect to the background star after the decade-old microlensing event.

Using the Keck II telescope in Hawaii, the team searched for the expected main-sequence lensing star, but no such star was found. Given the telescope’s sensitivity, that meant the lensing body could not be a main sequence star. A brown dwarf was ruled out because the source masses at least 0.15 the mass of the Sun. The upper end of the mass range, still below the mass of the Sun, ruled out a black hole or neutron star.

The analysis concluded they had found a white dwarf and a surviving planet that “represents an analog to the end stages of the Sun and Jupiter in our own Solar System.”

“We determine this system contains a 0.53 ± 0.11 solar mass white dwarf host orbited by a 1.4 ± 0.3 Jupiter mass planet,” they write in the paper’s abstract. “This system is evidence that planets around white dwarfs can survive the giant and asymptotic giant phases of their host’s evolution, and supports the prediction that over half of white dwarfs are predicted to have Jovian planetary companions.”





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