The sun sustains all life on Earth, but that’s not going to be the case forever. Eventually, the sun will exhaust its nuclear fuel and expand to engulf Earth and the other inner planets on its way to becoming a burnt-out cinder known as a white dwarf. It may also form a planetary nebula like NGC 6302, also known as the Butterfly Nebula. Scientists have long wondered what caused the unique shape of this object from which it gets its name. A new analysis of Hubble Space Telescope images has offered some tantalizing clues.
The Butterfly Nebula is so-named because the clouds of dust and gas have formed a pair of roughly symmetrical projections that look like wings. Most planetary nebulae formed by a dying star are round, which has made NGC 6302 a popular observational target since its discovery in the early 20th century. NASA even made the Butterfly Nebula one of the first objects observed by Hubble. The wings are about three light-years across, and the nebula sits 3,500 light-years away from Earth.
Since there are so many observational records of the nebula, researchers from the University of Washington were able to compare them to see how the butterfly’s wings have changed. Comparing Hubble images of the wings from 2009 and 2020, the team found marked changes to the structure. This indicates the white dwarf at the center of the Butterfly Nebula is still making waves.
The rippling features show how the Butterfly Nebula continues to grow and change due to jets emanating from the central white dwarf. (Credit: University of Washington/NASA)
The central star is notable all on its own for being one of the hottest in the known universe, with a surface temperature in excess of 250,000 degrees Celsius (200 times hotter than the sun). The team identified multiple jets of material being released by the star from 2,300 and 900 years ago — odd behavior for a white dwarf. These gusts push material toward the edges of the nebula at speeds up to 500 miles per second (800 kilometers per second). However, the matter closer to the white dwarf is moving outward 10 times more slowly. the mechanism behind the jets is still unclear.
The jets formed swirls and currents that crisscross over thousands of years, pushing current models of nebular formation to their limits. While the unexpected bursts from the white dwarf help explain some of the Butterfly Nebula’s distinctiveness, they don’t explain how the “wings” formed in the first place. The team speculates that the star may have collided with a smaller companion star or absorbed a cloud of gas, but it’s going to take more analysis, possibly with the help of the James Webb Space Telescope, to know for certain.
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