V Hya is a carbon star on the asymptotic giant branch (AGB). Stars on the AGB have left the main sequence, gone through the red giant phase, and moved past the horizontal branch (see Figure 2). Now in this last phase of hydrogen burning, these stars have a carbon-oxygen core (hence the name carbon star) and are surrounded by outer shells of hydrogen and helium. As these outer layers continue nuclear fusion, pulsations of the star can lead to changes in magnitude. Eventually, the pulsations "blow away" the outer shells and what is left behind is a white dwarf surrounded by a cloud of gas and dust. This is known as a planetary nebula (no, it has nothing to do with planets, this is just a historical name based on early observations).
V Hya is a peculiar case in that it has been observed by the Hubble Space Telescope to periodically fire "bullets" (high speed collimated jets). Astronomers have hypothesized that these emissions are due to a low-mass companion star with an eccentric orbit. When the companion is at its closest approach (periastron), the interaction (possibly the magnetic field interaction) between the two objects produces the jet. In a recent submission to the Monthly Notices of the Royal Astronomical Society, Salas et al. 2019 created a model to run many simulations of the system with varying parameters. They found it is likely that this is a triple star system. In this scenario, the emissions are due to the Eccentric Kozai-Lidov (EKL) mechanism Basically, when the outer most component is on a sufficiently distant orbit, it can influence the inner two objects creating perturbations in their orbits. According to Salas et al. 2019, this is a better fit for V Hya based on the Hubble data. More research will be needed to confirm their results.
References
Sahai, R. et al. (2016), https://arxiv.org/abs/1605.06728
Salas, J. M. et al. (2019), https://arxiv.org/pdf/1902.08206.pdf
