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Gas clouds in interstellar space can take on strange shapes. This rectangular
void (arrowed) in the constellation of Pegasus occurs in the clouds of ‘infrared
cirrus’ discovered in the Milky Way by the Infrared Astronomical Satellite.

The picture is a composite of several observations made at wavelengths
of 12, 60 and 100 micrometres. The void, which is about 400 light years
away, is about 7 light years across.

According to Lee Rickard of the US Naval Research Laboratory in Washington
DC it appears to be cold dust – at a temperature of about -250 °C –
which is obscuring light from stars behind it. He says that the rectangle
‘is a coherent structure and not a chance superposition’. However, he adds:
‘I have no explanation for it.’