New Delhi: Astronomers have used two flagship deep space observatories, the James Webb Space Telescope and the Hubble Space Telescope to examine the circumstellar disc surrounding Vega, a blue-white star about 40 times brighter than the Sun. The star is surrounded by a debris disc 160 billion kilometres wide, that is unlike the circumstellar discs discovered around young stars, where planets are being assembled. There is no evidence of any planets being assembled in the disc surrounding Vega, which are regions marked by dark belts where a newly forming planet is accreting the material leftover from the birth of the star.
Hubble image of the circumstellar disc. (Image Credit: NASA, ESA, CSA, STScI, S. Wolff (University of Arizona), K. Su (University of Arizona), A. Gáspár (University of Arizona)).
The infrared glow from the material surrounding the star can be picked up by Webb, while Hubble has captured the outer halo of the disc, which has particles as fine as smoke. These particles are reflecting sunlight. The energetic outpourings from the star causes a layered distribution of dust throughout the debris disc. The energies from the star is pushing away the surrounding material, and is sorting the particles by size in the process. At a distance of about 60 AU from the star, or about twice the distance Neptune is from the Sun, there are the subtle signs of a planet being formed. Apart from this subtle feature, the disk is entirely smooth.
Planetary construction yards
Scientists are interested in finding out why Vega is not forming planets around it, even though similar stars with similar chemical compositions do. Hubble started discovering circumstellar discs around stars in the mid-1990s. Most debris discs are spotted in orbit around newborn stars, made up of the leftover material from star formation. However, Vega is a matured star with a dusky disc, where interactions between the particles in the disc cause them to break down further. Vega is around 450 million years old, which is about a tenth of the age of the Sun.
