After its shape was revealed in the 1970s, astronomers were captivated by the Butterfly Nebula, one of our galaxy’s most spectacular stellar phenomena. Yet its heart remained hidden, cloaked in a dense shroud of dust.
Now, Nasa’s James Webb Space Telescope (JWST) has peered through that veil to uncover the ancient core of a dying sun-like star – the engine that causes the nebula to glow.
The results may offer a preview of the fate of our own sun. In about five billion years, when it runs out of fuel, it too could form a “planetary nebula”, enveloped in a vast, luminous cocoon.
Scientists in the UK designed, built and tested Miri in partnership with Nasa
“These results may have given us a glimpse of the future, of what our sun could potentially turn into — and it’s full of surprises,” said Dr Olivia Jones of the UK Astronomy Technology Centre.
The breakthrough comes courtesy of the mid-infrared instrument (Miri), one of JWST’s four main scientific tools.
Developed and built largely in the UK, it detects and analyses mid-infrared light — wavelengths longer than those that are visible. This allows astronomers to study faint and distant objects and to see through dust clouds that block traditional optical observatories.
Miri was able to look deep into the nebula’s core, which is about 3,400 light years from Earth, uncovering not only the central star but also a riot of activity around it.
This kind of nebula forms when stars with masses between roughly 0.8 and 8 times that of the sun expand and shed their outer layers at the end of their lives. The stage we see today is fleeting in cosmic terms, lasting about 20,000 years. The butterfly’s “wings” cover a distance of about 3 light years; the central star is just a few thousand kilometres across but its surface is incredibly hot, at roughly 220,000C.
Miri combines high-resolution imaging with spectroscopy, which measured the light at different wavelengths to determine the chemical composition, temperature and physical conditions of the nebula. Its observations show crystalline silicates, including quartz, forming in the central “torus” structure from which the butterfly’s wings extend. Jets rich in iron and nickel blast outward.
The mid-infrared instrument allows JWST to see objects obscured by dust clouds
JAMES WEBB TELESCOPE
Polycyclic aromatic hydrocarbons were also detected. On Earth these are found in smoke and burnt toast. It is the first evidence of such molecules developing within a planetary nebula.
“We were surprised at just how dynamic the nebula is,” said Dr Mikako Matsuura, from Cardiff University and lead author of the study. “The typical assumption is that planetary nebulae exist in a state of inactivity … Instead, we see what resemble both cool gemstones formed in calm, long-lasting zones and fiery grime created in violent, fast-moving parts of space, all within a single object.”
The term planetary nebula is a misnomer, dating from when earlier observers thought them planet-like in shape. The Butterfly Nebula is a bipolar nebula, meaning that it has two lobes that spread in opposite directions like wings. The dark band of dusty gas that forms the butterfly’s body is the torus, which is actually doughnut-shaped and being viewed from the side. The dusty doughnut may have caused the insect-like shape, by preventing gas from flowing outward from the star equally in all directions.