In twelve years time the universe looks set to offer us an exceptionally rare opportunity to discover if there are any planets orbiting Alpha Centauri A, one of the two nearest Sun-like stars to our own.
General relativity predicts that gravity can distort the path of light. When correctly positioned, a heavy object bends light around it to act as a lens, giving us a better view of whatever is behind it. The nature of the bending also tells us a lot about the distorting object. One of the ways we have discovered planets around other stars is by watching the parent star act as a gravitational lens for objects towards the center of the galaxy, and noticed the extra blip provided by the planet itself.
Usually, however, even the closer star is a long way from Earth. Discovering their planets has been useful in building statistics on planetary size and locations, but interest in individual discoveries was more muted. One of the closest stars to Earth passing in front of an object that would allow it to act as a gravitational lens would be a different matter entirely.
Kervella's team plotted the movements of both stars in the double system across our field of view. They made an extensive study of the background objects they will pass, and concluded that in May 2028 Alpha Centauri A will pass almost directly in front of the star 2MASS 14392160-6049528 (nicknamed S5). The timing is particularly fortuitous, since Alpha Centauri will be high in the sky at night, and the two stars will be widely separated, so that Alpha Centauri B's light will not interfere.
The paths of Alpha Centauri A (orange) and B (red) across the sky, with the objects one or the other star will pass in front of marked. Kervella et al Astronomy and Astrophysics