A newly discovered planet is 13 times the mass of Jupiter and orbits an unusual binary system composed of a red dwarf and a white dwarf. Most remarkably, there is a possibility the planet coalesced from the material the predecessor of the white dwarf threw off as it died.
KIC 10544976 is a pair of stars, one of which has gone through its entire life cycle to end up as a white dwarf, sometimes known as a dead star.
Less massive stars evolve more slowly, and the other member of the pair is a red dwarf with 39 percent of the Sun's mass and most of its life ahead of it. The two orbit each other every 8.4 hours, but there is also a much longer period wobble to their movements. We know about this because the pair eclipse each other as seen from Earth, but not always quite at the times we expect.
The red dwarf is also very magnetically active, with a cycle like our own Sun's 11-year pattern of storms and sunspot activity.
After years of observing the system astronomers had two competing explanations for the variations in the eclipse timing. Either the magnetic cycle of the red dwarf was interfering with the pair's movements, or they have a planet massive enough to affect them gravitationally.
Dr Leonardo Andrade de Almeida of the São Paulo Research Foundation reports in the Astronomical Journal that the red dwarf's period was calculated based on both the flares it emits and the cycle of starspots on its surface. Both give an answer of around 600 days, a period that could not explain the eclipse variations.
This leaves the possibility of a planet whose gravity is affecting the orbits. The variations we see are consistent with an object at least 13.4 times the mass of Jupiter and an orbital period of 17 years. Such enormous planets are rare but certainly not unknown, so the claim is realistic.
"The system is unique," Almeida said in a statement. "No similar system has enough data to let us calculate orbital period variation and magnetic cycle activity for the live star."
The process by which a star turns into a white dwarf is highly disruptive to planets. It's possible the planet formed in the normal way, at the same time as the stars, and survived the transformation of one of its parents by being so distant.
A far more intriguing theory is that this planet coalesced out of the material the predecessor star threw off on its path to becoming a white dwarf. Almeida believes the Giant Magellan Telescope, currently under construction, may be capable of seeing this planet directly, and possibly settling which possibility is right.