Twin Planets Orbit Star Pair

Artist impression of a planet orbiting a binary star system composed of a red dwarf star and a white dwarf star. Credit: South African Astronomical Observatory

Drs. Stephen Potter and Encarni Romero-Colmenero from the South African Astronomical Observatory (SAAO) and collaborators have found evidence for the existence of an extraordinary planetary system where two giant planets are orbiting a close pair of "suns".

If confirmed, this will be an example of a very strange planetary system, given the nature of the stellar pair. The two stars, a white dwarf and a red dwarf, are each smaller than our sun and are so close that they take only a couple of hours to orbit each other. The pair of them would actually fit comfortably within our sun.

By chance, the system is oriented in such a way that the stars appear to eclipse each other once every orbit as viewed from Earth. Dr. Potter and his collaborators noticed that the eclipses were not occurring on time, but were sometimes too early or too late. This led them to hypothesize the presence of two giant planets whose gravitational effect would cause the stars’ orbit to wobble and consequently slightly alter the measured time between eclipses.

The astronomers were also able to infer that the masses of the two planets must be at least 6 and 8 times that of Jupiter and take 16 and 5 years respectively to orbit the two stars. The system is too far away from us to be imaged directly.

This binary star system (known as UZ For) would be an extremely inhospitable environment. Due to their close proximity, the gravity of the white dwarf is constantly "stealing" material from the surface of the red dwarf in a continuous stream. This stream crashes onto the white dwarf where it gets super-heated to millions of degrees and subsequently floods the entire planetary system with enormous amounts of deadly X-rays.

This discovery was made possible by new SAAO and Southern African Large Telescope (SALT) observations combined with archival data spanning 27 years, gathered from multiple observatories and satellites.

Read more: Possible detection of two giant extrasolar planets orbiting the eclipsing polar UZ Fornacis