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Teardrops in the sky

Is it a comet? Is it a spaceship? The object in this Picture of the Week might be a bit hard to recognise at first. It is in fact a young star — but why does it have such an unusual shape?

Young stars are surrounded by a disc of gas and dust: the building materials for planets. When other very bright and massive stars are present nearby, their light heats the young star’s disc, stripping away part of its material. The teardrop-shaped object in this image, 177-341 W, is in the Orion Nebula. The stars eroding away the disc of 177-341 W are out of the frame past the upper-right corner; when their radiation clashes with the material around the young star, it creates the bright, bow-like structure seen here in yellow. The tail extending from the star towards the lower-left corner is material being dragged away from 177-341 W by the stars out of the field of view. This type of objects — ionised protoplanetary discs — are known as “proplyds”.

This observation is presented in a new paper led by Mari-Liis Aru (ESO) and taken with the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO’s Very Large Telescope (VLT) in Chile. The colours shown in this image map different elements like hydrogen, nitrogen, sulfur and oxygen. But this is just a small fraction of all the data gathered by MUSE, which actually takes thousands of images at different colours or wavelengths simultaneously. This allows astronomers to study the physical properties of protoplanetary discs in great detail, including the amount of mass that they lose. This new paper presents MUSE observations of many other proplyds in Orion, part of a project led by Carlo F. Manara (ESO) which will help astronomers understand how stars and planetary systems form in these stellar nurseries.