Wednesday 6 December 2023

A James Webb Space Telescope image of Protostar HH 797.

An image taken by the James Webb Space Telescope shows Herbig Haro object 797 (HH 797) in previously unseen detail. A Herbig Haro object is an elongate gas nebula formed by jets of gas blown on the stellar winds emerging from the poles of a young protostar colliding with gas and dust left over from the cloud from which the star formed at speeds of several hundred kilometres per second.

HH 797, a narrow, horizontal nebula that stretches from edge to edge of the lower half of the image. NASA/ESA/CSA.

HH 797 lies close to the IC 348 star-forming region within the constellation of Perseus, which is a little over a thousand light years from Earth. The IC 348 cluster is about 2 million years old, and contains about 400 stars, about half of which still have circumstellar disks.

HH 797 cannot be seen at visible wavelengths, as it is still buried within the cloud of dust and gas from which it has formed; the James Webb image has been taken in the infra-red part of the spectrum, collecting light emitted by excited hydrogen and carbon monoxide molecules heated to thousands of degrees centigrade by the interaction of the gas jets and the surrounding cloud.

The light emitted by the gas at the southern end of the plumes (bottom right) has been shown to be slightly red shifted as it reaches us, implying that the southern end of the plume is moving away from us, while the light from the gas at the northern end of the plume (bottom left) is slightly blue shifted, indicating that it is moving towards us.

The central part of the HH 797 nebula, from which the gas plumes are emerging. The protostar itself is invisible, creating a dark area. NASA/ESA/CSA.

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