Using W. M. Keck Observatory on Hawaiʻi Island, astronomers have captured the most detailed and complete images of the zone where the famed constellation of Orion gets zapped with ultraviolet (UV) radiation from massive young stars.
Known as the Photo-Dissociation Region (PDR), this irradiated neutral zone is in the Orion Bar within the Orion Nebula, an active star-forming site found in the middle of the “sword” hanging from Orion’s “belt.” When examined via a telescope, the beautiful nebula is shown to be a luminous gaseous stellar nursery- 1,350 light-years away from Earth, frequently mistaken for one of the constellation’s stars when seen with the naked eye.
Carlos Alvarez, a staff astronomer at Keck Observatory and co-author of the study, said, “It was thrilling being the first, together with my colleagues of the ‘PDRs4All’ James Webb Space Telescope team, to see the sharpest images of the Orion Bar ever taken in the near-infrared.”
As the Orion Nebula is the closest massive star formation region to us, scientists assume that it may be similar to the environment in which our solar system was born. Studying its Photo-Dissociation Region (PDR) is an ideal place to find clues about how stars and planets are created.
Emilie Habart, an Institut d’Astrophysique Spatiale associate professor at Paris-Saclay University and lead author of a paper on this study, said, “Observing photo-dissociation regions is like looking into our past. These regions are important because they allow us to understand how young stars influence the gas and dust cloud they are born in, particularly sites where stars, like the Sun, form.”
The second-generation Near-Infrared Camera (NIRC2) from Keck Observatory, along with the Keck II telescope’s adaptive optics technology, were employed by the PDRs4All team to study Orion’s PDR. The Orion Bar’s various substructures, such as ridges, filaments, globules, and proplyds (externally illuminated photoevaporating discs around young stars), that formed as starlight blasted and sculpted the nebula’s mixture of gas and dust, could be spatially resolved and distinguished by the researchers as a result of their successful imaging of the area.
This is the first time scientists could observe at a small scale how interstellar matter structures depend on their environments, particularly how planetary systems could form in environments strongly irradiated by massive stars. This may help them understand the heritage of the interstellar medium in planetary systems, namely our origins.
Scientists noted, “The new Keck Observatory images of the Orion Bar will help us understand this process because they reveal in detail where gas in its PDR changes from hot ionized gas, to warm atomic, to cold molecular gas. Mapping this conversion is important because the dense, cold molecular gas is the fuel needed for star formation.”