The Mid-Infrared Instrument (MIRI), managed until its launch by NASA-JPL, helped reveal small-scale structures at the edge of the nebula for the first time.
NASA’s James Webb Space Telescope has captured the sharpest infrared images to date of a magnified portion of one of the most distinctive objects in our skies, the Horsehead Nebula. These observations show the top of the “horsehair,” or edge of this iconic nebula, in a whole new light, capturing the complexity of the region with unprecedented spatial resolution.
Webb’s new images show part of the sky in the constellation Orion (“The Hunter”), on the western side of a dense region known as the Orion B molecular cloud. Out of the turbulent waves of dust and gas emerges the Head Nebula. de Caballo, also known as Barnard 33, which is located about 1,300 light-years away.
The nebula formed from the collapse of an interstellar cloud of material and shines because it is illuminated by a nearby hot star. The gas clouds surrounding Horsehead have already dissipated, but the protruding pillar is made up of thick clumps of material and is therefore more difficult to erode. Astronomers estimate that Horsehead has about 5 million years left before it disintegrates. Webb’s new view focuses on the illuminated edge of the top of the nebula’s distinctive structure of dust and gas.
The Horsehead Nebula is a known photodissociation region or PDR. In such a region, ultraviolet (UV) light from young, massive stars creates a warm, mostly neutral zone of gas and dust between the fully ionized gas surrounding massive stars and the clouds in which they are born. This UV radiation greatly influences the chemistry of these regions and acts as an important source of heat.
These regions occur where the interstellar gas is dense enough to remain mostly neutral, but not dense enough to prevent the penetration of UV light from massive stars. The light emitted by these PDRs constitutes a unique tool to study the physical and chemical processes that drive the evolution of interstellar matter in our galaxy and throughout the universe, from the first epoch of vigorous star formation to the present day.
Due to its proximity and almost edge-on geometry, the Horsehead Nebula is an ideal target for astronomers to study the physical structures of PDRs and the molecular evolution of gas and dust within their respective environments, as well as the regions transition between them. It is considered one of the best regions of the sky to study how radiation interacts with interstellar matter.
Using Webb’s MIRI and NIRCam instruments, an international team of astronomers has revealed for the first time the small-scale structures of Horsehead’s illuminated edge. As the ultraviolet light evaporates the dust cloud, the dust particles are swept out of the cloud, carried away with the heated gas. Webb has detected a network of fine features that trace this movement. The observations have also allowed astronomers to investigate how the dust blocks and emits light, and to better understand the multidimensional shape of the nebula.
