The v Octantis binary star system contains an interesting giant planet. This is the conclusion reached by an international team of astronomers studying this planet with the HARPS spectrometer. It turned out to be retrograde, that is, it spins in the opposite direction to the spin of its star.

v Octantis binary system
A small international team of astronomers has discovered a new exoplanet in the v Octantis system. This gas giant is unusual because it is retrograde, that is, it spins in the opposite direction to the spin of the star itself. The researchers drew an interesting conclusion from this and outlined it in a paper published in the journal Nature.
The v Octantis system consists of two luminaries: a subgiant and a white dwarf. The existence of a strange signal between them was first recorded back in 2004, but since then no one has been able to confirm that it is indeed a planet.
But the researchers used the HARPS spectrograph located at the European Southern Observatory in Chile and confirmed: the planet is indeed there. Moreover, it is a gas giant, twice as massive as Jupiter, that orbits around the larger of the stars.
Retrograde motion and the mystery of formation
The most amazing thing about this planet is its retrograde motion. And we’re not talking about a visible “backward motion” in the sky, as in the case of Mercury, but a real dynamic feature: the planet orbits the star in a direction opposite to the orbit of the star itself.
Ordinarily, this would never happen. But the presence of a white dwarf in the system also hints at a possible scenario. This star was once an ordinary star — on the main sequence, then went through a red giant stage before shedding its outer shells, becoming a white dwarf. It is this turbulent history of the star that is probably the reason for the planet’s retrograde motion.
Actually, there are two main versions. According to the first one, the planet first orbited around both stars, and after shedding its shells, it changed its orbit. According to the second, it originated from a secondary protoplanetary disk that formed around the subgiant due to ejected matter.
According to phys.org