New Delhi: The Hubble Space Telescope has turned its sensitive gaze towards a binary system of symbiotic stars at a distance of 700 lightyears, designated as R Aquarii. The R Aquarii system consists of a ageing red giant star and a white dwarf, which is the burning core of a white dwarf that has shed its outer layers in a violent eruption. The red giant is classified as a Mira variable star and has ballooned to 400 times the diameter of the Sun. This bloated monster is pulsating, with variations in temperature that causes rhythmic variations in its brightness by a factor of 750, over a roughly 390 day period. At its peak brightness, the red giant shines about 5,000 times brighter than the Sun.
Hubble’s capture of R Aquarii in 1990, which was its first image of a recent nova. (Image Credit: NASA/ESA/STScI).
The white dwarf in the system vampirically feeds on the hot hydrogen gas from the outer atmosphere of the red giant. When this accreted material hits a certain limit, it undergoes spontaneous nuclear fusion, making the entire surface of the white giant a nuclear bomb, violently shedding all the accumulated plasma. Then, the cycle repeats again. These filaments of plasma shed from the white dwarf are glowing because of the injection of heat from both the stars in the R Aquarii system. Hubble first observed the system in 1990.
Proximity of R Aquarii allows detailed study
R Aquarii is one of the closest known binary systems of symbiotic stars, and was in fact studied by none other than Edwin Hubble, the namesake of the Hubble Space Telescope. Hubble and his colleagues were able to determine that the white dwarf in the system erupted in a supernova around 600 years ago, with the regular nova events following since then, with the last one estimated to have taken place in the 1970s. The outer layers of gas in the image is made up of the plasma siphoned off from the red giant, and subsequently ejected by the white dwarf.
