There have been thousands of exoplanets found orbiting around single – or ‘normal’ – stars, but there have also been exoplanets found around binary or multiple star systems, as well as more exotic type stars. A new study published in the Monthly Notices of the Royal Astronomical Society presents a new way to detect dim objects – including exoplanets – orbiting exotic binary stars, also known as Cataclysmic Variables (CVs).
Cataclysmic Variables (CVs) are binary star systems, in which the two stars are in extremely close proximity to each other, so much so that the less massive star transfers mass to the more massive star. CVs are usually composed of a small, cool type star – a red dwarf – and a hot, dense star – a white dwarf. Red dwarf stars are approximately 0.07-0.30 times the mass of the Sun, and approximately 20% of the radius of the Sun, whereas white dwarf stars are approximately 0.75 times the mass of the Sun, with a radius similar to the size of the planet Earth. White dwarf stars are actually the remnants of solar-mass stars that are at the end stages of their lives. The transfer of mass – or matter – from the small star to the more massive star forms an accretion disk – a disk of hot plasma – that orbits around the compact, more massive star. The brightness of a CV system is dominated by this hot accretion disk, and overpowers the light being emitted by the stars themselves.
In this new study, the team of astronomers suggests that exoplanets could be detected in orbit around CVs by observing how the brightness of the CV system changes over time. If a third body were to exist in orbit around the CV, it could influence the rate of mass transfer between the two stars, and hence the brightness of the overall system. This new method to detect exoplanets around CVs would be based on the change of the brightness of the system due to perturbations in the accretion disk caused by the third body orbiting the two inner stars of the CV system.
In the work, the team studied brightness variations over long periods of time for four different CVs. The team was able to estimate the mass and distance of a third body orbiting these CVs. They noticed that the brightness variations had much longer periods of variability in comparison to the length of the orbital periods of the third bodies. Of the four systems, two of the CVs seem to have bodies that resemble planetary bodies, i.e., they have masses that are in the same regime as observed exoplanets. The team suggests that this is a promising new technique for finding exoplanets in orbit around exotic binary star systems.
Source: Royal Astronomical Society