THE PUZZLE OF TABBY ’S STAR
ASTRONOMERS love puzzles and the Universe has plenty. But few rival the mindbending mystery of a Sun-like star officially named KIC 8462852.
Usually known as Tabby’s star after the lead astronomer involved in its discovery, American Tabetha Boyajian, it’s been recorded in photographic star atlases since the 19th century. But its odd behaviour was revealed in a very 21st-century way, by NASA’s Kepler space telescope, which has been hugely successful in finding the planets of distant stars by observing regular dips in their brightness as orbiting objects passed in front of them. In 2015 the telescope revealed that Tabby’s star showed truly weird behaviour. Rather than regular 1 per cent brightness dips,Tabby’s star has irregular dips of up to 22 per cent. An early theory was that perhaps an alien megastructure was built around it – an energy-harvesting device known as a Dyson ring.Telescopes were deployed to search for artificial radio signals or laser light pulses, but none were found.Then, in 2017, analysis of infrared and ultraviolet light from Tabby’s star proved no solid object could explain its odd behaviour.
Dusty clouds were no answer either as the dust rings known to be around some stars couldn’t account for the irregular fading. Neither could obstructions such as debris from colliding planets.
Then, late last year, a new model proposed that a large dusty moon, stripped from its parent planet to become a ‘ploonet’, is now orbiting Tabby. Heated to melting point by the star, the ploonet could produce exactly the observed light changes. The challenge now is to seek similar stars to see if the model holds up.