An image captured by the James Webb Space Telescope portrays Herbig-Haro 46/47, or simply HH 46/47, a nebula of ionized gas that emits a faint light in which two lobes are very bright instead. The two numbers are due to the fact that there are two young stars still growing in the middle of a disk of gas and dust. Webb’s NIRCam (Near-Infrared Camera) instrument captured details of that area never seen before. The nebula is invisible at optical frequencies and is blue at infrared. The most spectacular part is the one characteristic of the Herbig-Haro objects with the ionized stellar winds forming two lobes visible in the image in orange hues.
Nearly 1,500 light-years from Earth, HH 46/47 is close enough to have been studied on many occasions since the 1950s. Herbig-Haro objects represent a short phase in astronomical terms, no more than a few hundred thousand years, in a star’s evolution. While they’re still forming, stars are very active and can emit jets of gas that is ionized by the shock waves generated by the collision with other slower-traveling gas. This process forms the typical lobes of Herbig-Haro objects. Gas emissions are inconstant therefore they change over time with differences that are appreciable even after a few years.
The presence of large amounts of gas and dust obscures much of the electromagnetic emissions from a Herbig-Haro object making it difficult to peer into the cocoons surrounding those newborn stars and protostars even when they are in the cosmic neighborhood like HH 46/47. Infrared is among the few that pass through those cocoons, so the James Webb Space Telescope’s superior performance in that electromagnetic band is invaluable in studying these objects.
The gas ejection processes by the protostars generate the typical lobes of Herbig-Haro objects creating extraordinary cosmic shows and are crucial in their evolution. The amount of gas ejected determines the star’s final mass as much as the amount of gas engulfed. This is a chaotic process and is why the lobes of these objects have such irregular shapes.
The blue nebula, invisible at optical frequencies, is technically called a Bok globule because it’s a type of cloud in which one or more stars are forming first observed by astronomer Bart Bok. Thanks to the James Webb Space Telescope, it’s possible to see through that nebula, which is why stars and galaxies behind it also appear in the image. The nebula also affects the shape of the lobes because the gas ejected by the young stars also collides with the gas in the nebula itself.
Monitoring irregularities and asymmetries in the lobes of object HH 46/47 is useful to understand the processes that are leading to the formation of the two stars. Star formation processes are among the most studied but their extremely long times on the human scale and the distances of newborn stars and protostars require continuous observations. In the case of the Herbig-Haro objects, results from the James Webb Space Telescope have only just begun to offer new insights.
