New Delhi: The James Webb Space Telescope has observed an embryonic star or protostar designated as Sharpless 2-284 in the outer edge of the Milky Way, with a pair of twin jets measuring eight lightyears across. For context, this is twice the distance between the Sun and its closest stellar neighbour. The plasma jets are being blasted into space with powerful magnetic fields confining the material to narrow beams. The size and strength of the protostellar jets makes them rare in comparison to similar jets seen from other stars in the early stages of stellar evolution. The outflows are streaking across space at velocities of hundredsd of thousands of kilometers per hour. The central protostar contains as much mass as ten Suns, and is located about 15,000 lightyears from the fringes of the galaxy.
The polar jets from the protostar have resulted in a unique class of stellar fireworks known as Herbig-Haro (HH) objects, that are considered to be the ‘birth announcement’ of stars to the universe. The star is building up mass by accumulating hot gas or plasma, with some of the infalling material being blasted outwards because of the spin of the star. There are over 300 HH objects known, but most of these are from low-mass stars. These polar jets offer clues about the newly forming stars. Scientists can study the energetics, narrowness and evolutionary timescales of the HH objects to constrain models of the environment in which the star is being formed, as well as the properties of the star itself.
HH jets scale with stellar masses
The observations suggest that the strength of the HH jets increase with the masses of the star. The more massive the stellar engine propelling the infalling plasma, the larger is the size of the plasma gushing out. Webb, with its exquisite sensitivity to infrared light has revealed fine filamentary structures within the jets. Like most HH objects, the jets from the protostar are ploughing into the gas and dust in the surrounding nebula, the raw material from which new stars are formed. There are a few hundred stars being formed in the stellar nursery, along with Sh2-284. The jets have been propagating outwards for over 100,000 years.