Ground-based telescopes make the nebula pictured here look rectangular in shape, hence its name: the Red Rectangle. But images taken by the Hubble Space Telescope revealed that it should more accurately be called the “Red X” nebula. The nebula’s unique shape comes from gas and dust emitted in cone-shaped bursts from the dying star at its center. This star, which began shedding its outer layers about 14,000 years ago, will slowly become smaller and hotter and begin to release a flood of ultraviolet light.
Photograph courtesy NASA/ESA/Hans Van Winckel (Catholic University of Leuven, Belgium)/Martin Cohen (University of California, Berkeley)
HD 44179: The Red Rectangle Nebula
The star HD 44179, located about 2 300 light-years away in the constellation Monoceros is surrounded by an extraordinary structure known as the Red Rectangle. This strikingly detailed Hubble image reveals how, when seen from space, the nebula, rather than being rectangular, is shaped like an X with additional complex structures of spaced lines of glowing gas, a little like the rungs of a ladder.
The star at the centre is similar to the Sun, but at the end of its lifetime, pumping out gas and other material to make the nebula, and giving it the distinctive shape. It also appears that the star is a close binary that is surrounded by a dense torus of dust — both of which may help to explain the very curious shape.
Precisely how the central engine of this remarkable and unique object spun the gossamer threads of nebulosity remains mysterious. It is likely that precessing jets of material played a role.
The Red Rectangle is an unusual example of what is known as a proto-planetary nebula. These are old stars, on their way to becoming planetary nebulae. Once the expulsion of mass is complete a very hot white dwarf star will remain and its brilliant ultraviolet radiation will cause the surrounding gas to glow.