Artist's impression of the protoplanetary disc around TW Hydrae
This illustration depicts the protoplanetary disc around the nearby young star TW Hydrae. With an age of about ten million years, TW Hydrae is located about 180 light-years away, towards the constellation Hydra, or the Sea Serpent.
Protoplanetary discs form around young stars from leftover material from the stellar formation process, which consists mainly of molecular hydrogen gas. This material orbits the star in a protoplanetary disc for several millions of years before it condenses into planets or is dispersed away by winds driven by the radiation of the star. In addition, trace amounts of cosmic dust and other gas species are present in the disc.
Astronomers using ESA's Herschel Space Observatory detected heavy molecular hydrogen in the protoplanetary disc around TW Hydrae, and have used this molecule as a tracer of the disc's main constituent – molecular hydrogen. This study has yielded the first accurate determination of the mass of a protoplanetary disc. With a mass equivalent to 50 times that of Jupiter, the disc around TW Hydrae is several times more massive than the primordial disc that gave birth to our Solar System.
At about ten million years, TW Hydrae is a relatively young star, but quite old to have retained a massive protoplanetary disc. The extremely accurate estimate of the disc's mass will benefit future observations of TW Hydrae and its environment, as astronomers investigate the various scenarios that could eventually lead to the formation of planets around this star.