Thursday, April 8, 2021

The Red Square Nebula

The Red Square Nebula (also known as MWC 922 and IRAS 18184-1302) is a nebula in the constellation of Serpens. Its distance is not known accurately, but it is believed that it ranges between 5,500-6,500 light years. The first images of this bipolar nebula were taken at Mount Palomar Observatory, and they were released in April 2007. The Red Square Nebula is notable for its square shape and its almost perfect symmetry. It surrounds a FS Canis Majoris star (i.e., a type of eruptive variable star), known as MWC 922 which belongs to the category of B[e] stars.

 This type of stars display neutral, or low ionization emission lines in their spectra, together with warm dust emission and molecular gas emission in the infrared. 

The evolutionary status of the source is not clear, thus both, pre- and post-main sequence statuses have been suggested. An explanation for the morphology of the Red Square Nebula, was suggested by Peter Tuthill and James Lloyd by suggesting that the shape of the nebula arises from two cones placed tip-to-tip seen from the side. The latter can also explain the double ring system that is around SN 1987A. 

Taking into account that FS Canis Majoris stars originate from binary stars and possibly as the result of stellar mergers, then it is quite likely that what we observe in the Red Square, is material that was ejected by the merger of a binary system. 

Image: Infrared image of the Red Square Nebula. The image was created using adaptive optics in the H-band (1.65 μm) combining data from the 200-inch telescope at Palomar Observatory, together with data from the 10-metre Keck telescope in Hawaii. 

Image Credit: Peter Tuthill, Sydney University Physics Dept., and the Palomar and W.M. Keck observatories.

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