ESA re-released this image this week (February 1, 2016). It’s called the Red Rectangle Nebula. ESA commented:
Straight lines do not often crop up in space. Whenever they do, they seem somehow incongruous and draw our attention. The Red Rectangle is one such mystery object.
It first caught astronomers’ attention in 1973. The star HD 44179 had been known since 1915 to be double, but it was only when a rocket flight carrying an infrared detector was turned its way that the red rectangle revealed itself.
This image was taken later, in 2007, by the Hubble Space Telescope’s Advanced Camera for Surveys. It focuses on wavelengths of red light, in particular highlighting the emission from hydrogen gas …
The Red Rectangle is some 2,300 light-years away in the constellation of Monoceros. It arises because one of the stars in HD 44179 is in the last stages of its life. It has puffed up as the nuclear reactions at its core have faltered, and this has resulted in it shedding its outer layers into space …
The X-shape revealed in this image suggests that something is preventing the uniform expansion of the star’s atmosphere. Instead, a thick disc of dust probably surrounds the star, funnelling the outflow into two wide cones.
The edges of these show up as the diagonal lines.
Thankfully, while that explains the mystery of the object, it does not detract from its unearthly beauty.
Bottom line: The Red Rectangle Nebula is a star in the last stages of its life. The star has puffed up and begun to shed its outer layers. The X-shape probably means something is preventing the uniform expansion of the star’s atmosphere, but what? No one knows for sure.
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.